Star Exam 2.0 Flashcards

Question

25. A vacuum breaker is used to avoid which of the following:

Answer 1

Negative gauge pressure

Answer 2

Prevent compressor short-cycling A lock-out relay is an electrically-operated control relay applied in such a way that it can “lockout” a circuit, or cause it to remain de-energized when once interrupted, as by some malfunction such as the tripping of a safety device. Lock-out relays may be either of two types: the normally-open type having a coil and a set of normally-open contacts, or the normally-closed type having a coil and a set of normally-closed contacts.

Answer 3

The run terminal and the common terminal A common type motor in fractional horsepower sizes is the split-phase induction motor, widely used in household refrigerators and small air conditioners. This type of motor has two windings; the main or running winding, and an auxiliary or starting winding. The running winding, located in the bottom of the stator slots, is made of many turns of relatively heavy wire; it therefore has little resistance but high inductance. The starting winding located at the top of the stator slots, has fewer turns of smaller wire, and so has higher resistance but less inductance. Inductance of the windings causes their current to lag the voltage, and since the running winding has more inductance than the starting winding, its current and magnetic forces reach their peaks later in each AC cycle than do the current and magnetic forces of the starting winding

Answer 4

All Makes a pump noisy Is the result of water boiling into the steam Is the result of insufficient NPSH Cavitation is a result of the insufficient available net positive suction head (NPSH) that causes low pressures, such that some of the pumped liquid flashes into vapor and forms bubbles. These bubbles are carried with the liquid as it goes through the pump, until they reach a region of higher pressure within the pump. Within this region, the bubbles collapse with a severe shock on the adjacent surface. This is called cavitation, and is accompanied by noises; vibration may also occur. The result is mechanical destruction of the pump in the form of pitting and erosion.

Answer 5

135 Btu. Heat = Weight (lbs.) x Specific Heat (Btu/lb. per degree) F x Temperature (degrees F) = 15 x1 (48-39) degrees F = 15 x 1 x 9 = 135 Btu

Answer 6

14.7 psi A column of this atmosphere one inch square and extending from sea level up to its maximum height (taken to be about 600 miles) weighs 14.7 pounds. Thus, the pressure at sea level is 14.7 psi.

Answer 7

A thermal cutout and a normal fuse link A dual-element fuse has a normal fuse link which will blow on a short circuit or very heavy overload. The second element in a dual-element fuse is a thermal cutout containing a connection that is held in place by low melting point solder.

Answer 8

Permanent-split capacitor motor Permanent-split capacitor motor. Some capacitor motors are constructed in the same manner as capacitor start motors except that they have no starting switch or relay; the capacitor and the starting winding are always connected.

Answer 9

Temperature-actuated When Reading a Symbol off of a wiring diagram it assumed that it is drawn in its de-energized state (no power applied). Temperature switches are drawn relative to a rise or fall in temperature. Switches above the points indicate a make or closure on temperature fall. Switches Below indicate a make or closure on a temperature rise.

Answer 10

Result in reduced refrigerant flow unless the valve is opened. Hand Valve A simple type of expansion device which can provide an orifice of variable size is a hand-operated valve. These were popular in ice plants that used ammonia. Their use was acceptable because of various reasons including the fact that there were always personnel available to adjust the valve, and plant efficiency was not very critical. The disadvantage of manually operated valves is their inability to automatically adjust the flow rate of refrigerant to suit the load and other operating conditions.

Answer 11

One contactor. Reduced Voltage Starting An “across-the-line” starter also known as a “full-voltage” starter, means that when the contactor closes, the motor is immediately connected directly to the power supply lines, and full voltage is at once impressed on the motor. This is the least expensive way to start a three-phase motor. However, this means that the motor will draw locked-rotor current until it starts turning. Although this is not of any consequence with most motors, the starting inrush current of large horsepower motors may cause the power system voltage to dip, resulting in flickering of lights and other objectionable effects on other electrical devices such as computers or television apparatus.

Answer 12

Not necessarily the same as the motor supply voltage An example of this would be in a high-voltage system (460 volts or higher) where a lower control voltage would be desirable for safety reasons or because some required control devices (such as thermostats, etc.) may not be available in higher voltage ratings. Another example would be where automatic control system is of low-voltage type, such as 24 volts. In such cases, the holding coils are obtainable in the lower voltage ratings desired.

Answer 13

An overload relay opens A lock-out relay is an electrically-operated control relay applied in such a way that it can "lockout" a circuit, or cause it to remain de-energized when once interrupted, as by some malfunction such as the tripping of a safety device.

Answer 14

Chilled water pump The chilled-water pump is manually started by pushing the start button. When the chilled-water pump is running, an auxiliary contact in its starter completes the circuit. If in the "continuous" position, the condenser-water pump will run whenever the chilled-water pump runs; if in the "automatic" position, the condenser-water pump will run on calls for cooling. The cooling-tower fan can be run at any time for test purposes by putting the control switch in "manual" position. For normal operation in "automatic" position, the cooling-tower fan can run on calls for cooling when the condenser pump is in operation. The interlock is accomplished through an auxiliary contact in the condenser-water pump starter which, upon closing, feeds control power to terminals in the machine control panel. The presence of control voltage at the terminals in the control panel also permits the lubricating oil pump to start, and when oil pressure has built up to normal, the compressor can start.

Answer 15

Be controlled by furnace bonnet temperature Bonnet temperature is sensed by the combination fan and limit control. As the bonnet warms up, the operating control switch will close, and start the fan. The main purpose of this control method is to keep the fan off until warm air is available, so that cold air will not be blown into the heated spaces.

Answer 16

Opposed blade operation Where throttling is required, a damper having opposed operation should be used. In this type of damper, adjacent blades rotate in opposite directions, resulting in a series of slots that become increasingly narrow as the damper closes.

Answer 17

Downstream

Answer 18

Negative gauge pressure A vacuum breaker is designed to prevent the pressure in the condensate return from dropping too low. If system pressure drops below 15 in.Hg, the breaker opens and lets air into the system. Since the pump draws from a tank that is vented to the atmosphere (to allow air to escape), it will typically see atmospheric pressure at the inlet and will be unaffected by system pressure.

Answer 19

0 The R value of the insulation when it is saturated with water has no insulation value.

Answer 20

Increase linearly The three main classifications of temperature sensors are: RTD (resistive temperature device), thermistor, and thermocouple. • RTD’s generally increase resistance linearly as temperatures rises (positive temperature coefficient). • Thermistors devices generally decrease resistance as temperature increases and are less linear then RTD’s. • Thermocouples create a voltage proportional to temperature change. They are constructed using two conductors made from dissimilar metals that are connected at one end. This junction point forms the tip of the temperature probe. Thermocouples are highly versatile and can be adapted for use in many applications.

Answer 21

To prevent damage to the control circuit What is a Surge Protector? A device that shields computer and other electronic devices from surges in electrical power, or transient voltage that flow from the power supply. Standard American voltage for home and office buildings is 120 volts. Anything over this amount is considered transient and can damage electronic devices that are plugged into an outlet. Even though power surges are so brief that they are measured in nanoseconds, they can cause considerable damage to electronic equipment. http://www.webopedia.com/TERM/S/surge_protector.html

Answer 22

500 microns. A vacuum pump capable of removing the atmosphere down to a very low vacuum is necessary. The vacuum pumps usually used in the refrigeration field are manufactured with rotary compressors. The pumps that produce the lowest vacuums are two-stage rotary vacuum pumps. These vacuum pumps are capable of reducing the pressure in a leak-free vessel down to 0.1 micron. It is not practical to pull a vacuum this low in a field-installed system because the refrigerant oil in the system will boil slightly and create vapor. The usual vacuum required by manufacturers is approximately 500 microns, although some may require a vacuum as low as 250 microns. Pulling a vacuum to a level of 500 microns will insure that all noncondensable have been removed from the system. This will insure that the system will not operate at a high head pressure or to be prone to acid formation.

Answer 23

746 watts Power and Energy Power means a rate of doing work. A common unit of mechanical power is the horsepower. For example, a ten-horsepower motor can do mechanical work, be it hoisting an elevator or turning the shaft of a compressor, at a faster rate than can a one-horsepower motor. The unit of power in the electrical circuit is the watt. It is equal to the voltage multiplied by the current. The formula is: Power = Voltage X Current or Watts = Volts X Amperes A common unit of electrical power is the kilowatt which is 1000 watts. Electrical power may be converted into mechanical power in an electric motor, or it may simply be turned into heat in a resistance. Equivalents are as follows: One kilowatt (KW) = 1.34 horsepower One watt = 3.413 Btu per hour One horsepower is 746 watts Energy is the amount of work done or explained. It is the product of the rate of doing work multiplied by a length of time during which work is done. The watt is the rate at which work is done electrically. The common unit of electrical energy is the watt-hour, this being a measure of the electrical energy consumed in one hour.

Answer 24

3.413 Btu Power and Energy Power means a rate of doing work. A common unit of mechanical power is the horsepower. For example, a ten-horsepower motor can do mechanical work, be it hoisting an elevator or turning the shaft of a compressor, at a faster rate than can a one-horsepower motor. The unit of power in the electrical circuit is the watt. It is equal to the voltage multiplied by the current. The formula is: Power = Voltage X Current or Watts = Volts X Amperes A common unit of electrical power is the kilowatt which is 1000 watts. Electrical power may be converted into mechanical power in an electric motor, or it may simply be turned into heat in a resistance. Equivalents are as follows: One kilowatt (KW) = 1.34 horsepower One watt = 3.413 Btu per hour One horsepower is 746 watts Energy is the amount of work done or explained. It is the product of the rate of doing work multiplied by a length of time during which work is done. The watt is the rate at which work is done electrically. The common unit of electrical energy is the watt-hour, this being a measure of the electrical energy consumed in one hour.

Answer 25

1,000 watts Power and Energy Power means a rate of doing work. A common unit of mechanical power is the horsepower. For example, a ten-horsepower motor can do mechanical work, be it hoisting an elevator or turning the shaft of a compressor, at a faster rate than can a one-horsepower motor. The unit of power in the electrical circuit is the watt. It is equal to the voltage multiplied by the current. The formula is: Power = Voltage X Current or Watts = Volts X Amperes A common unit of electrical power is the kilowatt which is 1000 watts. Electrical power may be converted into mechanical power in an electric motor, or it may simply be turned into heat in a resistance. Equivalents are as follows: One kilowatt (KW) = 1.34 horsepower One watt = 3.413 Btu per hour One horsepower is 746 watts Energy is the amount of work done or explained. It is the product of the rate of doing work multiplied by a length of time during which work is done. The watt is the rate at which work is done electrically. The common unit of electrical energy is the watt-hour, this being a measure of the electrical energy consumed in one hour.

Answer 26

Refrigerant friction through the evaporator The External Equalizer Superheat is abnormally high and serious loss of evaporator capacity results if the evaporator has any appreciable pressure drop. You might feel that you could compensate for the evaporator pressure by simply adjusting the valve, but this will not give the correct answer because the evaporator pressure drop varies. This pressure drop is due to friction developed when the refrigerant flows through the evaporator, just as friction is developed when a fluid flows through an ordinary pipe. Pressure drop at partial loads will be considerably less than at full load because of the smaller amount of refrigerant flowing at the lighter loads. The variable evaporator pressure drop is corrected for by sensing evaporator pressure, not at the evaporator or valve inlet, but at the evaporator outlet. This is done with a connecting tube called an external equalizer line, and is connected to a suitable fitting on the expansion valve. Such a fitting on an expansion valve should never be capped or plugged. If the valve has an external equalizer connection, an external equalizer line must be installed. The line should be connected to the suction line as close as practical to the bulb; specially, there should be no elbows, or other fittings which increase flow friction, between the equalizer line connection and the bulb. The purpose of the external equalizer line is to be able to sense suction pressure at the point where the bulb is located. In this respect, you should consider that it is possible for some liquid refrigerant to flow from the valve, through the equalizer line into the suction line. Since any liquid will vaporize at that point, the resulting cooling effect could influence the temperature sensed by the bulb. To avoid this, the equalizer line should connect to the suction line at a point a little downstream from the bulb.

Answer 27

Reclaiming Reclaim The definition of Reclaim is to reprocess refrigerant to new product specifications by means which may include distillation. It will require chemical analysis of the refrigerant to determine that appropriate product specifications are met. This term usually implies the use of processes or procedures available only at a reprocessing or manufacturing facility. Reclamation is required when the contamination of refrigerant is so severe that it does not meet industry standards. Offsite facilities can provide certification for reclaimed refrigerant and will meet the minimum standards required of ARI 700. The reclaim agent should provide information and cylinders to properly remove contaminated refrigerant from the system. They should also provide all pertinent information to ensure that the transfer and shipment of refrigerant meets all local, state and federal regulations. The EPA regulation prohibits the sale of CFCs and HCFCs that do not meet the minimum standards of ARI 700. Refrigerant transferred between owners must be reclaimed.

Answer 28

FT 3/LB An important concern of air conditioning systems is the quantity of heat that a system can add or remove. The quantity of heat transferred depends on three factors: the flow rate of the medium, its specific heat, and the temperature difference. Note that flow rate is based on lb. /hr., or the weight of air flowing in a given time. However, the design of duct and fan systems is based on volume (cfm) rather than weight, since ducts and fans must be of proper size to handle the necessary air volumes without objectionable results such as excessive pressure, velocity or noise. Also, the systems and equipment should be tested for proper flow. It is more readily possible to measure air-flow rates by volume than by weight. However, the volume occupied by a given weight of air changes whenever there is a change in its temperature or pressure. In order to eliminate numerous calculations as well as avoid confusion which these variables could cause, it is desirable to have a fixed reference point for such things as duct-design data, and for ratings of equipment such as air diffusers, fans, coils, filters, and other air treating apparatus. Such a reference point is standard air which is defined as dry air at pressure of 29.92 in.Hg (101.325 kPa) at exactly 68 degrees (20 degrees C) temperature. At these conditions, the density is 0.075 lb. /ft.3 (1.204 kg/m3). Based on this definition of standard air, the volume occupied by one pound of standard air is equal to 1 / 0.075, or 13.33 ft3.

Answer 29

1000 btu Performance and Water Usage Once-through systems typically require a water flow rate of about 1.5 gpm per ton, whereas recirculated systems such as those with cooling towers require three gpm per ton. In the once-through system, heat extraction depends entirely upon sensible heat gain of the water. Based on a 20-degree rise in water temperature there is a pick-up of 20 Btu per pound of water after which the water is disposed of.

Answer 30

When looking at the chart you will see that as the angle lessens the strain on the sling of the basket increase. The straighter the Basket the less strain.

Answer 31

Motor contacts A typical across the line starter has a set of contacts rated for the load in which is going to be operated. These Contacts are represented by a moving set and a stationary set within the device.

Answer 32

As built And are usually submitted upon job completion once all construction is complete and the building is commissioned. Drawing Interpretation and Plan Reading Chapter 6 Interpretation of Building plans

Answer 33

- (SPST) Single Pole Single Throw - (DPDT) Double Pole Double Throw Relays typically used in the HVAC have the capability to do multi functions through the selection of NO or NC contacts. Multi configured relays can simultaneously operate devices in a system. Its usage depends on its current carrying capacity across the contacts.

Answer 34

Contactor A Contactor can use low voltage control power to operate the switching type relay to operate a High current capacity device. Typically Contacts on the contactor are rated much higher than a Common relay’s internal contacts.

Answer 35

B. Incorrect: Pitting C. Incorrect: Wear due to Arcing D. Correct: Both B and C When inspecting a contactor contacts for both the moving and stationary points needs to be checked regularly for wear due to High Current arcing which occurs overtime when device starts and stops. High current readings may result from poor contact closure. Typically excessive wear will require replacement of the contactor or contactor points. Depends on their serviceability and size.

Answer 36

L1, L2, L3 When wiring the Starter the Line (Power supply) is landed on the “L” terminals of the starter typically labeled as L1, L2, L3. Most times located on the TOP portion of the device

Answer 37

T1, T2, T3 Load being operated by the starter is connected to the “T” terminals of the device. These terminals are located downstream of the electrical overloads internal of the device. Typically on the bottom of the starter labeled T1, T2, T3

Answer 38

M1 first Pushing P1 down energizes R1 relay coil, closing R1 normally open contacts, energizing TDR relay coil and R1 normally open contacts energizing M1 coil first. After TDR (Time Delay Relay) times out M2 coil energizes second.

Answer 39

Motor life A Variable Frequency Drive is an electronic device that controls the direction, speed, torque, and other operating functions of an electronic motor in addition to providing motor protection and Monitoring functions. Incorrect VFD set-up may result in motor life reduction. It however does not specifically control motor life.

Answer 40

Sizing Thou sizing could be a general problem when troubleshooting, reasons for problems could occur from improper application and selection. The location, for example, may be incorrect for operating conditions. Other reasons might include component, installation, or wiring issues

Answer 41

Energized, Voltage VFD’s need to be checked for proper operation during them being energized and running by means of Voltage reading as typically required in the areas of the drive for proper parameters to be met for it’s given application and use. Current cannot be detected in the de-energized state. Resistance reading should never be performed when any electrical system is energized and Voltage readings would not be possible when the VFD is not powered.

Answer 42

Increases When applying OHMS Law in an electrical circuit, substitute the values given in the formula to solve for the unknown. When asked what occurs when either one increases or decreases the values of the circuit reacts accordingly. Example use simple Numbers when calculating. *note the circuit needs to be a series circuit.

Answer 43

Goes to zero When applying OHMS Law in an electrical circuit, substitute the values given in the formula to solve for the unknown. When asked what occurs when either one increases or decreases the values of the circuit reacts accordingly. Example use simple Numbers when calculating. *note the circuit needs to be a series circuit.

Answer 44

Decreases When applying OHMS Law in an electrical circuit, substitute the values given in the formula to solve for the unknown. When asked what occurs when either one increases or decreases the values of the circuit reacts accordingly. Example use simple Numbers when calculating. *note the circuit needs to be a series circuit.

Answer 45

One male and one female rotor Most all helical screw compressors consist of 1 male and 1 female rotor while operating. When operating rotor should never touch one another as this will cause damage and lost efficiency due to scorn rotor passages. In some case there may be a possible 3rd rotor from manufacturers for increased capacity and efficiency.

Answer 46

- The slide valve and - Motor speed System capacity in a Helical Screw compressor is controlled by slide valve movement which adjusts the area in which refrigerant gas passes through the rotors during the operation. The more gas that is allowed to mover through the rotors the more capacity is performed. By use of VFD motors it too is possible to adjust capacity by means of controlling the speed of the rotors which when lowered allows less refrigerant gas to pass reducing capacity.

Answer 47

Increases When applying OHMS Law in an electrical circuit, substitute the values given in the formula to solve for the unknown. When asked what occurs when either one increases or decreases the values of the circuit reacts accordingly. Example use simple Numbers when calculating. *note the circuit needs to be a series circuit.

Answer 48

Increases When applying OHMS Law in an electrical circuit, substitute the values given in the formula to solve for the unknown. When asked what occurs when either one increases or decreases the values of the circuit reacts accordingly. Example use simple Numbers when calculating. *note the circuit needs to be a series circuit.

Answer 49

Keep your cool, learn as much as possible, but call your supervisor to report the incident When faced with a difficult customer your first objective is to not escalate the situation. In this case listen to customer and avoid getting into a verbal sparring match. If possible, try to finish the work that you have been called to perform. Let your supervisor know about the incident.

Answer 50

Sleeve bearing Sleeve bearings are reliable when used for small motors with light loads. Further, they offer quiet operation, which is important when used in applications close to the conditioned space.

Answer 51

A. Partially Correct: Oil that is too thin will allow the shaft to run against the bearing surface. B. Partially Correct: Oil that is too thick will not run into the clearance between the shaft and the bearing surface. C. Partially Correct: The correct oil allows the motor shaft to float on a film of oil between the shaft and bearing surface. D. Correct: All of the above.

Answer 52

Causes overheating. In fact, the most common cause of overheating in a ball bearing is excess grease.

Answer 53

Three feet.

Answer 54

One fourth.

Answer 55

Are most economical when controlled by an enthalpy controller. Enthalpy controls may be thought of as combination controllers containing dry-bulb thermostats that are reset by a relative humidity element. At any given outside dry-bulb temperature, the air’s moisture content and its total heat content may vary significantly. In other words, 70 degree F dry air might be quite capable of cooling a building while 70 degree F saturated air would contribute to the same building’s cooling load. Outside air enthalpy in the 21 btu/lb. to 24 btu/lb. range is normally considered adequate for comfort cooling of commercial buildings. Any combination of dry-bulb and wet-bulb temperatures providing enthalpy within that range will provide sufficient cooling.

Answer 56

Compressor capacity control is required. Face and bypass dampers used with cooling or heating coils provide a method of regulating the amount of cooling or heating obtained from the coil without the need to control the flow of the medium, such as water or steam, being supplied to the coil. This is an advantage with chilled water cooling coils, as any appreciable reduction in water flow would raise the temperature of the coil surface and rapidly reduce or eliminate the ability of the coil to condense moisture from the air, a necessary step for dehumidification. As the face damper decreases flow of air over the coil at reduced loads, it is necessary to keep suction pressure above freezing to keep ice from forming on the coil. One possible method of avoiding freezing coil temperatures would be compressor cylinder unloading according to suction pressure.

Answer 57

Amperage The ampere is the unit which represents the flow of electrons in an electrical circuit used to measure the flow of electrons in an electrical circuit.

Answer 58

Voltage The pressure differential in an electrical circuit is called the electromotive force (emf). This emf is measured in volts. The volt is the basic unit of potential difference.

Answer 59

Ohm The unit of resistance is the ohm, and the unit symbol is the Greek letter Omega. The letter symbol “R” is used to indicate resistance on schematic diagrams. All components in an electrical circuit contain some resistance to current flow.

Answer 60

Expansion device Typical Refrigeration Systems The basic vapor compression refrigeration cycle is applied in a number of ways. This basic cycle requires the use of four essential components ------ the evaporator, the compressor, the condenser, and the expansion device.

Answer 61

In parallel with contacts The cooling anticipator is wired in parallel with the thermostat contacts so that it is energized during the cooling “off” periods. The thermostat is calling for cooling by completing a circuit between terminals R and Y. Note that the cooling anticipator remains connected in the circuit but it has no effect because it is “shorted out” by the thermostat contacts. However, during the “off” periods, the heater is energized and falsely warms the thermostat, causing it to bring on cooling earlier than would occur without the anticipator. The result of this method of “heat anticipation” is that smaller amounts of heat are added or removed at more frequent intervals than occurs with ordinary two-position control. This results in a smaller differential.

Answer 62

Dehumidification Dehumidification is the process of removing moisture from the air, associated with the cooling or summer function of the system. Air can be dehumidified by bringing it into contact with a chemical that has an ability to absorb (or adsorb) water vapor, and this is sometimes done in industrial air conditioning where a high degree of dryness is needed. If necessary, however most dehumidification is done by cooling the air to a low enough temperature to cause some of the moisture to condense out as liquid water, just as dew is formed from the atmosphere.

Answer 63

Grilles Three basic types of air supply outlets are: 1. Grilles 2. Slot diffuser outlets 3. Ceiling diffusers The various types of outlets differ from one another in the amount of air entrainment and in the air distribution patterns produced. The type to be used depends partly on architectural design and on spaces available for duct. The type of outlet most desirable may also depend on the quantity of air to be supplied relative to the size of the room.

Answer 64

Air conditioning and refrigeration tube Air-Conditioning and Refrigeration Tube (ACR) Type ACR copper tube is designated for air-conditioning and refrigeration installations. It is clean, moisture free and capped when it leaves the manufacturer, thus insuring the installer a non-contaminated tube. ACR copper tube differs from the other two classes of copper tube in two major respects: it is available in a greater number of sizes (especially the smaller sizes); and the sizes specified are actual outside diameters. Therefore, its designated size is always 1/8-inch larger than the designated size of copper water and DWV tube with the outside diameter. That is, 1/4inch copper water tube has the same outside diameter as 3/8-inch ACR tube; 3/8-inch copper water tube has the same outside diameter as 1/2-inch ACR tube. Fittings used for ACR tube are the same as the fittings used for water tube. However, care should be exercised in ordering these fittings, because of the different method used in specifying the size of the tube. When ordering fittings of 7/8-inch ACR tube, it is necessary to order 3/4inch nominal or 7/8-inch O.D., which is the same as required for 3/4-inch copper water tube. The wall thickness of hard temper copper ACR tube are the same as that of Type L water tube. The wall thickness of annealed ACR tube are close to, but not exactly the same as that of Type L water tube. Air Conditioning and Refrigeration tube is made according to ASTM Standard B280.

Answer 65

Series A heat anticipator is a small electrical resistance heater placed in a thermostat. By adding heat to the thermostat at certain times of the operating cycle, depending on whether the thermostat is to control heating or cooling, it reduces the effect of the time lag. On a fall in temperature, the mercury bulb will tilt to complete R to terminal W to turn on heating. Note that the heating anticipator is in series with the thermostat contacts, so that the heater is energized during the “on” periods but is deenergized during the “off” periods. When energized during the “on” portions of the cycle, the thermostat is warmed not only by the warmer air but also by the heating anticipator. The thermostat therefore becomes satisfied sooner in each “on” cycle than it would if the anticipator was not present. The effect is to prematurely shorten the “on” periods.

Answer 66

ANS: 39.2 Solution: Use for Formula: Heat (Btu) = Weight (pounds) x Specific Heat (Btu per LB per degree F) x Temperature Difference (degrees F) = 20 x 0.49 x (31-27) degrees F = 20 x 0.49 x 4 = 39.2 Btu

Answer 67

ANS: 1000 V = 144 x cfm divided by a = 144 x 2250 (324,000) divided by 18 x18 (324) = 1000 fpm

Answer 68

There is gas in the liquid. The sight glass in a refrigeration system permits a view of the refrigerant at the sight glass location. Installed in a liquid line, the sight glass will show bubbling if there is any gas in the liquid refrigerant. If only liquid, without gas, is present, the glass will show clear. It should be cautioned, however, that the glass will also clear if there is only gas or no refrigerant at all present.

Answer 69

The test cock should discharge liquid refrigerant. Where liquid leaving the receiver flows vertically upward out of the receiver, an integral dip tube is an important feature of the receiver. The dip tube, connected to the receiver outlet, extends to about one-half inch from the bottom of the receiver. Its purpose is to ensure that only liquid enters the line leaving the receiver, preventing any vapor from entering the liquid line. If replacing or re-installing a receiver, it is essential to determine which connection has the dip tube. A receiver may not contain an integral dip tube, and so it may have to be provided in the field. The bottom end of the dip tube should not be made with a square cut; it should be cut-off at an angle of approximately 45 degrees. For this purpose, a receiver valve, can be used. The above considerations of the dip tube apply only to receivers where the liquid outlet is on the top of the receiver. If a receiver outlet is on the bottom of the receiver so that refrigerant can flow out by gravity, no special provision is needed to assure the liquid line being free of vapor; in such case, the dip tube must of course be omitted or only vapor would enter the liquid line.

Answer 70

Driers. Driers used in refrigeration systems are based on the principle of bringing refrigerant in contact with a material which is capable of catching and retaining the moisture. Such materials are called desiccants, and those used in refrigerant driers usually are able to remove acid as well as plain water. In use, the desiccant sooner or later reaches a point where it can hold no more moisture and/or acid; it then is ineffective and should be replaced. Desiccants that have been used in refrigeration systems have retained oil and acid as well as water, and it is not acceptable to reactivate them (chemically dry them out) for re-use; they should be discarded when no longer effective.

Answer 71

true South

Answer 72

Convection

Answer 73

Passive indirect

Answer 74

Passive direct

Answer 75

Jet type pump. The jet pump forces water through an injector that increases its velocity, creating a correspondingly low pressure around it, creating a suction that causes water to flow.

Answer 76

A. Partially Correct: Air. Partially correct. The pumps used are centrifugal pumps, which can be destroyed by cavitation. B. Partially Correct: Steam. A common reason for pump failure is live steam entering the pump due to failed steam traps. The cause of the pump failure must be corrected at the same time the pump is repaired or replace. If bad steam traps allowed the steam to reach the pump, the steam traps must be repaired or replaced or the new pump will soon fail again. Both air and steam can destroy a vacuum pump. However, through the design of vacuum steam heating vacuum pumps, air typically does not enter the pump. The intake of these pumps draw from a tank that is vented to the atmosphere. The vent is to allow air to escape. The pump intake is near the bottom of the tank, so only water is drawn into the pump. Further, pump cavitation is caused by low suction pressure. Since the intake of the pump is connected to a tank under atmospheric pressure, the pump does not see low suction pressures. Steam can reach the pump, however, if the steam traps allow live steam to blow by and enter the condensate lines.

Answer 77

A failed steam trap. A failed steam trap will allow live steam to blow by. If the steam makes it to the vacuum pump, it can destroy the pump. In buildings with many steam traps and poor maintenance procedures, failed steam traps are a common cause of a vacuum pump failure.

Answer 78

A. Partially Correct: Fuel/energy costs associated with producing steam. Other costs are also saved. B. Partially Correct: Boiler water make-up and sewage treatment. Other costs are also saved. C. Partially Correct: Boiler water chemical treatment. Other costs are also saved. D. Correct: All of the above.

Answer 79

A trap that is warmer than condensate temperature. A trap that is warmer than the condensate temperature indicates that steam is flowing freely through it, meaning that the trap is not trapping the steam as it is designed to do.

Answer 80

Place a clean pair of disposable covers over your shoes When entering a customer’s home you should always place shoe/boot covers on to protect floors from potential tracking of dirt, oil and grease.

Answer 81

Discuss what you have with the customer and your supervisor so that the customer can decide whether to authorize the additional repair It is always best to clear any additional work through the customer before going ahead with the repairs.

Answer 82

Form completed in legible hand writing & Complete list of materials used and amount of time spent on the The wholesale cost of the parts used on a job would not be listed on the work order.

Answer 83

The last thing that you should do before leaving the job After all work at the job has been completed and you have explained to the customer what repairs were performed you should request that the customer sign the work order acknowledging the work that was done.

Answer 84

Working safely on the worksite As an integral part of a work crew you have a responsibility to interact with the other individuals in a positive, cooperative and safe manner.

Answer 85

180 degrees F. A bearing hotter than 180 degrees F is an indication of possible trouble. Infrared thermometers can be used to quickly check for hot bearings.

Answer 86

A dial indicator. A runout gage is also used for measuring runout. & A runout gage. A dial indicator is also used for measuring runout.

Answer 87

Refrigerant from leaking out the rotating shaft. A function of a seal is to keep the refrigerant inside the system. & Oil from leaking out at the rotating shaft. A function of a seal is to keep the refrigerant inside the system

Answer 88

Polished steel surfaces and a carbon ring. It is the mating surfaces of the steel and carbon ring that form the seal in this type of seal.

Answer 89

Is accomplished using a string or straight edge. A straight edge or string can be used to run from one pulley to the other. Alignment is complete when the string or straight edge touches both pulleys in two places at once.

Answer 90

Chapter 5 Interpretation of Isometric Drawings

Answer 91

The employee who applied the lock or tag is not available at the workplace. The employer must confirm that the employee is not at the workplace to ensure, among other things, that the employee is not in danger of injury when the circuit is energized. & The employee who applied the lock or tag is aware that it has been removed before he or she resumes work at that workplace. The employer must ensure that the employee is aware that a circuit that he/she knew to be locked out is now energized.

Answer 92

July 1, 1992

Answer 93

10 in. Hg.

Answer 94

Recovered. The refrigerant must be recovered from the system before the system can be repaired. & Reclaimed. If a compressor burn has occurred, you should have the refrigerant reclaimed.

Answer 95

It also vents air and carbon dioxide continuously at steam pressure. During operation, steam, air, and CO2 rise to top of the inverted bucket. The steam condenses, but the air and CO2 remain a gas. When the valve at the top of the trap opens, the air and CO2 are the first to leave the trap.

Answer 96

Pipe friction. The friction of steam and condensate flowing along the pipe creates heat that re-flashes some of the condensate back to steam. & Reduced pressure. A drop in system pressure will lower the boiling point of the condensate and cause some of it to flash into steam. & A vertical rise in a condensate line. A vertical rise will lower the pressure of the condensate, thus lowering the boiling point, causing some of it to flash into steam. D. Correct: All of the above.

Answer 97

Let condensate escape by gravity from the fast-moving steam. There is another purpose. & Store condensate until it can be discharged through the steam trap. There is another purpose.

Answer 98

Water hammer and damaging slugs of condensate. Steam and condensate flowing in the same pipe can cause water hammer and in severe cases, actually destroy piping components leading to the discharge of live steam into the atmosphere.

Answer 99

2.31 Feet of head is equal to 1 psi. This is the same factor used in pumping calculations.

Answer 100

High velocity sound. Escaping steam will have a higher velocity sound than normal operation of the trap, be it continuous or intermittent. An electronic listening device can be used for this, although a simple screwdriver, with one end held against the trap and the other against your ear, works just as well. In either case, experience is required to distinguish between sounds of the trap and other sounds in the system.

Answer 101

The valve may have failed to seat because of wear or a piece of dirt or scale. A piece of dirt could be lodged between the valve and the valve seat, preventing the valve from closing and allowing steam to blow by. & The trap may have lost its prime. A sudden or frequent drop in steam pressure is usually the cause of prime loss. The installation of a check valve upstream of the trap can prevent this problem. & The bucket is stuck or has a hole in it. If the bucket is stuck in the down position for some reason, steam can fill it then blow by under the bottom of the bucket. If the bucket vent becomes oversized, steam can blow through the top of the bucket and blow out of the trap.

Answer 102

Equalizing line The water level in the equalizing line is the same as in the boiler, because the steam pressure on the top of both lines is the same. This prevents the boiler water from flowing out of the boiler into the return main.

Answer 103

Hartford Loop The Hartford Loop prevents water from dropping more than 2” to 4” below the normal operating water line (NOWL) through the condensate wet return line by breaking the siphoning effect once the water reaches that level.

Answer 104

3 The control valve is designed with a small percentage of change so there are no radical changes in the pressure and steam temperature in the system piping.

Answer 105

Two stage system Example of a Two-Stage Machine There are several arrangements of the two impellers used in two-stage centrifugal compressors. An impeller on each end of the motor shaft discharges gas from the first stage being conducted through a large pipe to the inlet of the second stage impeller. This arrangement is suitable for hermetic type machines.

Answer 106

Valve piped incorrectly The valve installation is very important and must be used whenever a control valve is installed. The valve installation law states that: The trim must always close against the flow. When piping two-way control valves, always make certain that the trim, especially the plug, will close against the direction of flow of the process fluid. The process fluid should always be trying to force the valve open. Control valves are stamped with a direction of flow arrow or the words inlet and outlet on the body. Failure to obey this law will result in objectionable water hammer and physical damage to the valve and piping system.

Answer 107

The superheat will be low If not enough refrigerant is being fed to the evaporator - the superheat will be high. If too much refrigerant is being fed to the evaporator - the superheat will be low. Too much refrigerant is being fed to the evaporator, perhaps so much that the liquid will reach the compressor. The cause may be due to the expansion valve not operating properly or it any be due to the compressor. 1. One of these systems may be attributed to improper expansion valve control. Installation and engineering faults, incorrectly installed external equalizer, undersized compressor, poor refrigerant distribution, etc. are all problems associated with low superheat, as well as high superheat. 2. Dirt or foreign material, filings, etc. will restrict the flow of refrigerant when it collects at the valve port, which can also prevent the valve from tightly closing. The foreign material must be removed and a filter should be installed to provide effective filtration of the refrigerant. 3. Capacity of Direct Expansion Coils. The capacity of a direct expansion coil depends upon the quantity of air passing through the coil, the dry and wet bulb temperatures of this air, and the temperature of the refrigerant. If the quantity of air is increased, the coil will have a greater capacity. Because of this increased capacity, the coil will be able to boil off or evaporate a greater quantity of refrigerant in a given time. On the other hand, if the quantity of air, or the temperature difference between the air and the refrigerant, is reduced, (dirty evaporator coil) the rate of refrigerant evaporation will decrease and the coil capacity will correspondingly decreased. Any increase in the rate of evaporation will cause an increase in the quantity of refrigerant vapor created, and if the compressor is running at constant speed, the increased vapor flow will raise the suction pressure. Conversely, any decrease in the rate of evaporation (dirty evaporator coil) will lower the suction pressure.

Answer 108

Compressor crankcase Oil Protection Control High speed refrigeration compressors require the use of a pump to maintain uniform flow of oil and oil pressure in the lubrication systems of compressors. An ordinary pressurestat connected to the oil pump discharge line should not be relied upon to stop the compressor if oil pressure is too low. The oil pump draws oil from the compressor crankcase and pumps it into oil passages, and after the oil has lubricated the necessary parts of the compressor it drains back to the crankcase (except for the small portion which leaves the compressor with the refrigerant). The oil system is subjected to compressor crankcase pressure which is also suction pressure, and a pressure gage connected to the oil pump discharge would read the combination of suction pressure plus the pressure developed by the oil pump; but such but such a reading would be meaningless because suction pressure varies according to operating conditions. However, if the difference between oil pump discharge pressure and crankcase pressure was measured, you would have an indication of the actual pressure that is causing the oil to flow within the compressor. The pressure difference is referred to as the useful oil pressure. The oil protection control (which may also be called an oil pressure failure control, or an oil safety switch) measures this pressure difference by the use of two bellows opposed to each other. Oil pump discharge pressure is exerted on one of the bellows, and suction pressure is exerted on the other bellows. The difference between these two pressures is the useful oil pressure. If this pressure is too low, the rod connecting the two bellows together will move so as to operate a switch to break an electric circuit and stop the compressor.

Answer 109

Oxidation inside the tubing Erection of Refrigerant Piping Systems Using Copper Tubing When all fittings and sections of tubing are ready to be brazed, they should be assembled and securely blocked in position, firmly supported, and properly aligned so that tubing is concentric within fittings. The next precaution to be observed is the prevention of forming copper oxide when the piping is heated. Even though every precaution may have been taken to avoid the presence of oxygen inside the piping, it must be assumed that some air, together with its oxygen, will have gotten into the piping by the time it is ready to be brazed. Silver brazing will require that the parts being brazed be heated to temperatures of 1100 degrees F to 1300 degrees F, and in the presence of oxygen, copper at such elevated temperatures will rapidly oxidize and form a scale. As previously discussed, this oxide scale is a contaminant which must be kept out of the system. The recommended procedure is to prevent the formation of scale by purging the pipe to be brazed with dry nitrogen. This method will replace the air with a gas which is inert and so the copper on the inside of the pipe will not oxidize. The nitrogen must be dry “oil-pumped” grade

Answer 110

Humidity and temperature Enthalpy controls may be thought of as combination controllers containing dry-bulb thermostats that are reset by a relative humidity element. At any given outside dry-bulb temperature, the air’s moisture content and its total heat content may vary significantly. In other words, 70 degree F dry air might be quite capable of cooling a building while 70 degree F saturated air would contribute to the same building’s cooling load. Outside air enthalpy in the 21 btu/lb. to 24 btu/lb. range is normally considered adequate for comfort cooling of commercial buildings. Any combination of dry-bulb and wet-bulb temperatures providing enthalpy within that range will provide sufficient cooling

Answer 111

Back seated Using the Gage Manifold For pressurized systems, a suggested procedure is: Locate usable pressure taps. Where compressors have service valves the valve gage ports would be used. In this case, the valve should be backseated to isolate the gage port from the system. Next, the plug or cap should be slowly removed from the gage port, and any residual pressure be allowed to vent to atmosphere. Then an adapter having a male flare fitting to which the manifold hose can be connected.

Answer 112

Oil Hermetic Compressor Motor Burnouts If motor failure is evident, it should be determined whether a burnout has occurred. Test kits such as Carrier Total test should be used for this purpose. The size and type of compressor will determine further procedures to confirm a burnout and to determine its extent. Burnouts are classed as mild or severe, depending upon the extent of clean-up recommended. A sample of the compressor oil should be checked for color and odor. It should also be checked for acidity using and acid test kit.

Answer 113

On the suction line as it leaves the evaporator Valve Location and Installation Unless instructed otherwise by the valve manufacturer, thermostatic expansion valves may be mounted in any position, although upright mounting with the power head on top is preferred. They should be installed as close as possible to the evaporator, and there should be no restrictions between the valve and the evaporator, other than a refrigerant distributor if used. Proper location of the thermal bulb is very important. Requirements for correct bulb installation are: The bulb should be close to the evaporator outlet. The bulb should always be installed in a horizontal line. If there is no way of avoiding installation on a vertical line, the bulb should be turned so that the capillary tube comes out at the top. The bulb should never be installed where liquid can trap. Liquid refrigerant or a mixture of liquid refrigerant and oil boiling out of the trap will give a false temperature rather than actual suction gas temperature. The suction line where the bulb is to be mounted should be cleaned, and the bulb should be securely attached with two clamps. Oil leaving the evaporator in an oil-refrigerant mixture generally flows along the lower portion of a horizontal suction line, and it is not good practice to place a bulb on the bottom of the line. It is preferable to locate the bulb on top of the line for lines 3/4 inch and smaller in size. On larger lines, it is generally recommended that the bulb be installed at a point midway down on the side of the line.

Answer 114

Suction pressure to rise and the discharge pressure to fall Multispeed Compressor Motors Since the capacity of a compressor is proportional to the compressor speed, one way of regulating capacity is to vary the speed of the compressor. One method of varying the speed of a compressor driven by an electric motor is to use a two-speed motor, two low-pressure switches, and a twospeed magnetic motor starter. At high suction pressure, indicating a heavy load, the compressor is operated at high speed. As the load decreases and suction pressure falls, one of the low pressure switches opens and changes the speed from high to low. Further decrease in load and suction pressure to a minimum causes the second low pressure switch to stop the compressor. Multiple Compressors One way to obtain capacity control is to use more than one compressor. For example, if a required capacity of 15 tons was split into three compressors each of five tons capacity, two compressors could run and have 67 percent capacity, or only one compressor and have 33 percent capacity; the one compressor could be cycled under on-off control for capacity below the 33 percent step. This is desirable in some installations where complete shutdown due to failure of equipment would cause serious financial loss. An example of this is a cold storage refrigerator where the refrigerated meat, milk, etc., could spoil if left without refrigeration. The use of multiple compressors provides standby service, and under partial load conditions only the number of compressors would be operated as required by the load on the system. Since unneeded compressors are completely stopped, the horsepower requirements of a multiple compressor system are reduced proportionately as load decreases. When multiple compressors are started in sequence, the draw of starting current is less than it would be to start one large compressor motor. This an advantage as it also allows the use of smaller electrical wiring. Another advantage is avoiding interruptions to electrical power systems which can occur when large motors are started. However, there is a lubrication problem if more than one compressor is to be connected to a single evaporator piping system. Unless pressures in the crankcases of the several are equalized, the oil will leave the crankcase having the highest pressure. Methods of equalizing pressures and oil levels require careful planning.

Answer 115

122.2 Solution: Ohms Law R=E divided by I 110 divided by 0.9 = 122.2 ohms

Answer 116

135 Solution: Heat = Weight (lbs.) x Specific Heat (btu/lb. per degree) F x Temperature Change (degrees F) = 15 x 1 (48-39) degrees f = 15 x 1x 9 = 135 Btu

Answer 117

9 Solution: RPM x D = rpm x d 580 x D = 1740 x 3 (5220) D = 1740 x 3 (5220) divided by 580 = 9 in.

Answer 118

ANS: 375,000 Solution: “Rule-of-thumb” figure for condenser heat rejection is 15,000 Btu per ton of net refrigeration effect. 25 tons x 15,000 Btu per ton = 375,000 Btu per hour

Answer 119

ANS: 50 Solution: Btuh = 500 x gpm x delta T 500,000 = 500 x 100 x delta T Delta T = 500,000 500 x 100 Delta T = 10 Leaving temperature = 40 + delta t Leaving temperature = 40 + 10 Leaving temperature = 50 degree F

Answer 120

5 Solution: Divide VA by volts 60 divided 12 = 5 amps.

Answer 121

34 Solution: Atmospheric press. (14.7 psi) = 33.95 (34) ft. Weight of column of water 1’ high (.433 lb. per foot) Theoretically, water can be pulled (raised) approximately 34’ vertically. The positive atmospheric pressure forces the liquid up the suction pipe towards the lower pressure at the pump connection. The partial vacuum in a pump is created by the piston in reciprocating pumps, by the cam or gear action in rotary pumps and in centrifugal pumps by the liquid being forced away from the center. The maximum practical suction lift on positive displacement pumps is 22’ and on centrifugal pumps it is 15’.

Answer 122

Partially Correct: Refrigerant from leaking out at the rotating shaft. A function of a seal is to keep the refrigerant inside the system. and Partially Correct: Oil from leaking out at the rotating shaft. A function of a seal is to keep the refrigerant inside the system.

Answer 123

So that the cause of the safety shutdown can be investigated prior to re-start. A function of a seal is to keep the refrigerant inside the system.

Answer 124

Flame rod. Flame rods are designed so that current is conducted in the flame is much stronger in one direction (half cycle) than in the other, which produces a rectified signal.

Answer 125

Heat the cylinder with a torch. You should never heat a cylinder with a torch, and should never raise the temperature above 125 degrees F.

Answer 126

Close; close; open. Both the evaporator pressure and the spring pressure act to close the valve, while the suction pressure from the bulb acts to open the valve.

Answer 127

Tighten the packing gland and/or replace the packing. In most cases, simply tightening the packing gland will minimize the leakage. Remember that this type of seal is designed to leak slightly, as water acts as a lubricant. If tightening the packing gland does not minimize the leak, the packing itself may be worn and need replacing.

Answer 128

Inlet pressure that is too low. Inlet pressure that falls below the manufacturer’s recommended net positive suction head (NPSH) will cause water to boil due to the low pressure, causing bubbles and cavitation.

Answer 129

Outlet pressure that is too high. A failed steam trap will allow live steam to blow by. If the steam makes it to the vacuum pump, it can destroy the pump. In buildings with many steam traps and poor maintenance procedures, failed steam traps are a common cause of vacuum pump failure.

Answer 130

Allow condensate to drain after the steam has been shut off. Once the steam supply has been shut off, steam will condense and will be unable to drain because of the vacuum. The vacuum breaker provides a vent and allows the condensate to drain

Answer 131

The bimetal relay and the melting alloy relay

Answer 132

Capillary action. Capillary action is the flow of a liquid when it is drawn into a small space between wetted surfaces. This is the same action that draws colored water into flowers during Biology experiences and allows trees to get water from the roots to the crown.

Answer 133

Destroyed Prior to each shift, a component person will inspect the sling and all fastenings and attachments for damage or defects. Inspections will continue as warranted during use. The competent person will immediately remove damaged or defective slings from service and keep documentation on the inspections. If any member of the crew sees a defect in rigging, he or she should not wait for the competent person to inspect it. The defective rigging should be immediately removed from service.

Answer 134

Counter-clockwise until the tension is off Pressure adjusting screw. The regulator adjusting screw controls the flow of gas and delivery pressure to the hose and torch. As previously stated, the regulators function to reduce high supply pressures to a suitable working pressure range. When adjusting screw is turned clockwise, the regulator will allow gases to flow through the regulator to the hoses and to the torch. The threaded adjusting screw allows mechanical force to be applied to a spring which controls a flow valve in the regulator. If the adjusting screw is turned counterclockwise, tension on the spring is released and the regulator will not allow the gas to flow.

Answer 135

Superheat Calculating superheat example using R-22. NOTE: To arrive at the correct superheat reading, take the following steps. A. Note the suction pressure or evaporating pressure reading from the suction gage: 69 psig. B. Convert the suction pressure reading to suction or evaporating temperature using the pressure/temperature chart (PT chart) for R-22: 40 degrees F. C. Use a suitable thermometer to record the actual temperature of the suction line: 50 degrees F. D. Subtract the saturated suction line temperature from the actual suction line temperature: 50 degrees F - 40 degrees F = 10 degrees F of superheat.

Answer 136

Oxygen Some precautions which must be taken when leak testing are: 1. Nitrogen must be oil-pumped dry nitrogen. 2. Although carbon dioxide (CO2) could be used instead of nitrogen, never use oxygen or acetylene. 3. When using high-pressure gas such as nitrogen or carbon-dioxide in cylinders, always use a pressure regulator and a relief valve.

Answer 137

A. Partially Correct: Time B. Partially Correct: Pressure C. Partially Correct: Temperature D. Correct: Any of the above Defrost Timer. Defrost cycles are initiated at periodic intervals as, for example, every three hours. The timer contains an electric clock which turns cams to operate one or more switches. Although it is standard practice to initiate defrost cycles according to time intervals, there are several ways by which the defrost cycle is terminated: Time-terminated. The timer automatically returns the system to normal operation after a set number of minutes on defrost. Temperature-termination. A remote-bulb thermostat senses the temperature of the evaporator coil surface. An accumulation of ice and frost will lower the coil surface temperature and upon being defrosted the temperature will rise to normal. The thermostat senses the temperature rise and terminates the defrost cycle, the timer will do so after a set elapse of time. Pressure-terminated. When the evaporator has lost its capacity because of a coating of ice and frost, there will be a decrease in suction pressure. However, defrosting will restore ability of the evaporator to boil off refrigerant, so that suction pressure will rise. Suction pressure can be sensed by the defrost control and it will terminate the defrost cycle when suction pressure rises to normal. A possible difficulty is that if the suction line is exposed to a low ambient temperature or if it is cooled because of being installed near cold refrigerant lines, the suction pressure may remain low even though the evaporator is defrosted. Therefore, defrost controls usually include a fail-safe feature which automatically terminates the defrost cycle after a set elapse of time, even though suction pressure may not have risen enough to cause a pressure-termination of the cycle.

Answer 138

The compressor to be overheated. The term heat exchanger is a general one, applying to a device in any kind of mechanical system that transfers heat from one medium to another. However, as referred to specially refrigeration, a heat exchanger means a device to transfer heat from the liquid to the relatively cooler suction vapor. Precautions. 1. Heat exchangers must be constructed and installed so as not to trap oil. 2. The amount of superheating should be limited, as excessive superheating of suction gas will cause excessive discharge temperature and overheat the compressor. This effect can be readily checked on Pressure-Enthalpy Charts. This precaution is especially important for hermetic motor-compressors, since the motors are cooled by the suction vapor. 3. HCFC-22 Systems: Heat exchangers ordinarily are not to be used in systems using HCFC-22. The usual condensing pressures are quite high with normal evaporator superheat, and further increase in superheat would raise discharge pressure and temperature so high as to overheat the compressor and damage the discharge valves. If an unusual lowtemperature application should require a heat exchanger, it is considered good practice to provide a valve bypass line around the exchanger, to adjust flows so as to reduce any compressor overheating which may occur. 4. Heat exchangers should not be indiscriminately added to systems. Their use without proper investigation of system design and engineering can lead to compressor damage.

Answer 139

Trap liquid refrigerant. In some applications, such as heat pumps and hot-gas defrost systems, it is anticipated that in normal operation there will at times be liquid floodback from the evaporator. The suction accumulator can be used to protect the compressor against entry of liquid in such cases where, although only occasional, the quantities of liquid are fairly large so that they could not be immediately evaporated in a heat exchanger. The suction accumulator is installed in the suction line between the evaporator and the compressor. It is basically a tank; a slug of liquid refrigerant and/or oil leaving the evaporator will be trapped in the accumulator.

Answer 140

Compressor. When reciprocating compressors are in normal operation, their pistons and piston rings ride on a film of lubricating oil. A small quantity of the oil is pushed through the cylinders and leaves the compressor along with the discharge gas. The oil must be returned to the compressor. An oil separator is a tank-like device which removes oil from the refrigerant and automatically returns the oil to the compressor.

Answer 141

Parallel and angular. Shafts must be aligned so that the centerlines meet each other exactly in the center (parallel to one another, or axially), and they must be aligned so that they have no angular difference between them (also called radical alignment).

Answer 142

A. Partially Correct: The compressor will not compress. There are other symptoms. B. Partially Correct: The compressor will stop on motor overload. There are other symptoms.

Answer 143

A p-trap Problems can occur in getting oil to flow upward in certain vertical piping, and a trap at the bottom of the riser can assist in getting the oil to begin the upward flow. Another purpose of a trap is to prevent oil in certain lines from draining back to the compressor during the off-cycle.

Answer 144

30 degrees F to 35 degrees F Air-cooled condensers have a relationship to the temperature of the air passing over them. The refrigerant inside the coil will normally condense at 30 degrees F higher than the air passing over it (also known as the ambient air). This statement is true for most standard-efficiency condensers that have been in service long enough to have a typical dirt deposit on the fins and tubing. The relationship can be improved by adding condenser surface area. With the outside air temperature of 95 degrees F, the condensing temperature will be about 125 degrees F.

Answer 145

Dividing discharge pressure absolute by suction pressure absolute The compression ratio of a compressor is the ratio of the absolute discharge pressure (psia) to the absolute suction pressure (psia): Compression Ratio = Discharge pressure, psia Suction pressure, psia Note that compression ratio is always based on absolute pressures.

Answer 146

15,000 As a “rule of thumb, “ it has long been considered that the heat rejection from an air conditioning system is about 15,000 Btu per hour for every 12,000 Btu per hour of cooling capacity, or 15,000 divided by 12,000 equals 1.25 times the net refrigeration effect.

Answer 147

12 degrees F to 15 degrees F Adjustment of a thermostatic expansion valve means adjusting the spring tension so that the valve controls at the desired value of superheat. The proper value of superheat is usually established by the manufacturers of the equipment, and their recommendations should be followed. As a general rule, the superheat setting for a relatively high temperature application, such as air conditioning, might be 10 to 15 degrees; for low temperature applications, the superheat probably should not exceed 10 degrees.

Answer 148

Bulb opens, spring closes, evaporator closes the valve The three fundamental pressures which affect the opening and closing of the thermostatic expansion valve are: 1) Bulb pressure, 2) Evaporator pressure, and 3) Spring pressure. Bulb pressure works through the capillary tube on the top of valve diaphragm and it acts to open the expansion valve. The evaporator pressure works under the diaphragm in the direction of closing the valve. This pressure is equal to the pressure which corresponds with the refrigerant saturation temperature. Spring pressure also acts to close the expansion valve. This pressure is transmitted through the top of the pin carrier and the push rods to the underside of the diaphragm.

Answer 149

Mid seated Refrigeration Mechanical Equipment Service Manual Volume One In order to read the pressure at the gage port while the compressor is running, the valve should be back-seated, and then turned in one or two turns to slightly open the connection to the gage port. The compressor is always open to either the line or the gage port, or both if the valve is neither front-seated nor back-seated.

Answer 150

27,304 The unit of measurement for electrical power is the watt (W). Converting electric heat rated in kilowatts (kW) to the equivalent gas or oil heat rated in Btu. Suppose that we know the capacity in Btu for a 20-kW electric heater (a kilowatt is 1000 watts). 1 kW = 3413 Btu. 20 kW X 3413 Btu/kW = 68,260 Btu of heat energy Converting Btu to kW. Suppose that a gas or oil furnace has an output capacity of 100,000 Btu/h. Since 3413 Btu = 1 kW, we have 100,000 Btu divided by 3413 Btu/kW = 29.3 kW In other words, a 29.3 -kW electric heat system would be required to replace the 100,000-Btu/h furnace. 3.413 Btu = 1 W. 1 kW (1000 W) 3.413 X 1000 = 3413 Btu. 3413 Btu x 8 kW = 27,304 Btu’s

Answer 151

Outside temperature and humidity sensor. An enthalpy sensor reacts to the total heat content of air, both sensible and latent energy.

Answer 152

In parallel to with load The voltmeter is designed much like the ammeter, but a resistor is added to the circuit to prevent a direct short and to allow electrons to flow in the meter. The voltmeter uses two leads that are connected to jacks which lead to internal wiring. In order to obtain a reading, the two leads must touch or be connected to the conductors supplying the load or to the circuit that transfers the emf to the meter.

Answer 153

Apply clamp-on amp meter around wire Motor amperage is measure by clamping the jaws of the meter around one of the motor power wires.

Answer 154

Check voltage with a good meter High voltages and currents are present that may cause serious injury or extensive equipment damage. Be certain that all power has been turned off, locked out, and tagged in any situation where you must actually come in contact with the circuit or equipment. Make sure that the circuit cannot be turned on by anyone but you. Use only well designed and well maintained equipment to test, repair, and maintain electrical systems and equipment. Use appropriate safety equipment such as safety glasses, insulating gloves, flash suits, hard hats, insulating mats, etc. when working on electrical circuits. Make sure that multimeters used for working on power circuits contain adequate protection on all inputs, including fuse protection on ALL current measurements input jacks.

Answer 155

Parallel A voltmeter is used to measure voltage drop, or a potential difference, across any part of a circuit. A voltmeter is always connected across a device (in parallel). The voltmeter can be used to measure the voltage drop across any of several devices which make up the total load.

Answer 156

6 amps When the source of EMF provides a constant potential difference in the circuit and the temperature is constant, current is inversely proportional to resistance; when resistance goes up, current goes down; when resistance goes down, current goes up. The three forms of Ohm’s Law follow: Chapter 6: Electrical Systems and Controls Review Exam I-109. Question 10. Pages 197 and 198.

Answer 157

Watts Electrical power relates to the time rate of doing work. The definition of electrical wattage is 1 watt of power is used to perform work when 1 volt causes 1 ampere of current flow for 1 second. The letter P is used to represent electrical power. Power is measured in units of the watt. The formula for electric power is: P = E x I Transformers are rated in Volt - Amps Transformer Rating = VA VA = Voltage x Amperage Example: VA = 24 Volts x 2 amps, VA = 48VA

Answer 158

Circuit breaker There are two major types of circuit protectors, fuses and circuit breakers. A fuse is used in a circuit to protect the wiring against overloads. An overload occurs whenever there is too much current for the size of the wire. This could happen if too many loads are plugged into the same circuit. The other type of circuit protector is the circuit breaker. Some circuit breakers look much like a switch. They usually have a lever with an ON and OFF position. When in the ON position, current flows through a thermal device within the breaker. If excessive current passes through this device, it heats up. If the thermal element gets too hot, it trips the breaker. When the breaker is tripped, the lever is in the OFF position and the circuit is open. After the thermal element has cooled sufficiently, the breaker can be manually reset to close the circuit again. Another type of circuit breaker looks like a regular strip fuse with a button protruding from the top. When this breaker trips, it can be manually reset by pressing the button.

Answer 159

C. Partially Correct: Amperage D. Partially Correct: Current E. Correct: Both C and D are correct The simplest fuse is a metal conductor with a low melting point. When excessive current flows through the circuit, the fuse begins to heat up. When the temperature reaches the melting point, the conductor melts (blows), breaking the circuit. Fuses are sized according to the amount of amperage they will carry without breaking the circuit. A 15 amp fuse will conduct up to 15 amperes. If too much load is plugged into the circuit, or a short drawing more than 15 amps occurs, the fuse will blow. Fuses come in many different amperage ratings. Never use a larger fuse than the circuit is rated for. An oversized fuse does not protect a circuit.

Answer 160

Primary winding Transformers are available in a variety of capacities for stepping-up or stepping down AC voltages. The construction of a step-down transformer is simple. Windings of insulated wire and placed around one side of an iron core. This winding is connected to the power source and is called the primary winding. Another separate winding of insulated wire is placed opposite of the core. This is called the secondary winding. There is no physical electrical connection between the primary and secondary of the transformer. Electrical energy is transferred from primary windings to secondary windings by the process of induction.

Answer 161

Load, switches The relay is composed of two devices: 1. The coil portion, which is a load and performs work (the action of physically moving a switch). 2. A switch that controls the power source to another load.

Answer 162

Permit any zone to have year round heating or cooling Three principal advantages of reheat systems are: 1. They provide simultaneous sources of both cooling and heating, so that room or zone temperature can be controlled, no matter whether cooling or heating is needed to obtain the desired temperature. 2. They readily provide as many zones of control as may be desired, including control of each individual room, simply by providing the necessary number of coils and their heat source and controls. 3. They have the ability to maintain close control of humidity in the conditioned space, based on adequate control of the dew point of air supplied by the central apparatus.

Answer 163

Control space temperature by regulating the flow of air to each zone A variable air volume system has a terminal unit which contains an automatic damper by means of which the zone supply air quantity is varied. The automatic damper is under control of a thermostat which senses the temperature in the area or zone supplied by the terminal unit.

Answer 164

Maintain a stable discharge volume regardless of supply duct pressure Minimum and maximum limits can be readily obtained with volume regulators, by mechanical stops on mechanical volume regulators, or by setting of adjustment stops on pneumatic volume regulators. Separate maximum volume limiters are also available for pneumatic systems such limiters sense velocity as indicated by a difference between total and static pressure of air in the terminal unit inlet, and act to limit the pneumatic air pressure supplied to the damper actuator. A maximum volume limiter for electric control systems is wired into a control circuit and operates as follows: Excess velocity pressure closes a switch in the limiter which overrides the zone thermostat to drive the damper toward the closed position until velocity pressure and velocity drop to the predetermined value.

Answer 165

A. Partially Correct: Are able to supply each zone with heated or cooled air in all seasons B. Partially Correct: Are less economical to operate than VAV systems C. Partially Correct: Can have their hot deck temperature reset on coldest zone demand D. Correct: All of the above Multiple-path systems have more than one path for the conditioned air supply, making it possible for the central apparatus to provide air at more than one temperature. The multizone system uses a central air apparatus of the blow-through type. The supply fan discharges air through either the cooling coil or the heating coil, or air in varying proportions through each coil. A disadvantage of multi-path systems is loss in operating economy compared to some other systems, the variable air volume system for instance. A cold deck thermostat and hot deck thermostat each maintain their set point temperatures year-round. The cold deck temperature is set at a low enough temperature, typically about 55 degrees F, to provide cooling capacity equal to the design cooling load. The hot deck temperature is set high enough typically about 120 degrees F, to satisfy the design heating load. Refrigeration and heating equipment is operated to satisfy the demands of the deck thermostats. In practice, heating may be turned off in season of extreme cooling loads, and mechanical refrigeration turned off in extreme heating seasons. In intermediate seasons, all equipment should be operated so that the zone thermostats will be able to mix cold air and warm air to satisfy zone requirements. This provides good temperature control, but the need for using energy to heat air for partially neutralizing air on which energy has been expended to cool it, or vice versa, it is not an economical process. A method used for refining the control system is by adding outdoor reset control. Hot deck temperature is reduced as outdoor temperature rises.

Answer 166

Have their hot deck temperature reset by outside air temperature or on coldest zone demand A cold deck thermostat and hot deck thermostat each maintain their set point temperatures year-round. The cold deck temperature is set at a low enough temperature, typically about 55 degrees F, to provide cooling capacity equal to the design cooling load. The hot deck temperature is set high enough typically about 120 degrees F, to satisfy the design heating load. Refrigeration and heating equipment is operated to satisfy the demands of the deck thermostats. In practice, heating may be turned off in season of extreme cooling loads, and mechanical refrigeration turned off in extreme heating seasons. In intermediate seasons, all equipment should be operated so that the zone thermostats will be able to mix cold air and warm air to satisfy zone requirements. This provides good temperature control, but the need for using energy to heat air for partially neutralizing air on which energy has been expended to cool it, or vice versa, it is not an economical process. A method used for refining the control system is by adding outdoor reset control. Hot deck temperature is reduced as outdoor temperature rises.

Answer 167

Be used with a variable capacity squirrel cage fan Morning warm-up. If the building has been unoccupied at night or over a weekend during cold weather, the temperature in areas served by the variable air volume system may become uncomfortably cool. It may be necessary to supply warm air through the system for a short period of time until lights have been turned on and the building becomes occupied. Since the system is designed to supply less air in response to falling room temperature, the VAV dampers will have moved to their closed or minimum positions and depending on the controls used, the warm air may or may not be able to flow through the terminal units and into the space unless special provisions are made. If all terminals are constructed and adjusted to provide a minimum open position, warm-up may be obtained by simply supplying warm air for an adequate period prior to occupancy.

Answer 168

Reduce starting current inrush Because of the problems caused by large starting currents, it is often necessary to limit the amount of power that can be drawn in starting large motors. Another although less common reason for limiting starting power occurs in some applications where the mechanical shock resulting from full-power starts could cause damage to the driven equipment. Essentially, limiting the power at start-up means that locked-rotor current must be reduced, and several types of starters are used for this purpose. These usually employ some means of reducing the voltage that is impressed on the individual motor windings at start-up. Such starters are consequently referred to as reduced voltage starters (as opposed to full-voltage starters, a term often applied to across-the-line starters).

Answer 169

The motor is never disconnected from the line during starting Arranging the transfer so that the motor is never disconnected from the line during the starting period can eliminate this objection. The latter arrangement is called closed transition. Electric utility companies may demand closed transition starting when using such reduced voltage starters. Closed transition is achieved by proper sequence operation of the contacts, so that the motor is never disconnected from the line.

Answer 170

Manual reset type Manual reset is preferred, however because it requires the operator to look for the cause of the overload.

Answer 171

Manual reset type Another basic requirement of a motor controller is that it should provide motor protection. There are some exceptions to this, as will be discussed later, but the protection of the motor against over-current is a very common requirement of a motor controller. You have seen that the fuses (or circuit breakers) that are used to protect the feeders (branch circuits) are capable of carrying starting and running currents of the motor. Such branch-circuit protection will protect the motor from short-circuit currents, but will not adequately protect the motor against overheating due to currents that are less than short-circuit currents but which exceed the rated current of the motor.

Answer 172

Hottest water during the coldest weather When the outside temperature is low, the hot water or warm air must be at a high temperature, but to avoid overheating, it is desirable that the water or air not be quite as hot during mild weather.

Answer 173

Decreases as outdoor air gets colder In air-to-air heat pumps, the outdoor coil, which is the condenser in the cooling cycle, becomes the evaporator when the heat pump is used for heating. In the latter operation, whenever the outdoor-coil temperature reaches 32 degrees or colder, ice can form on the coil and will accumulate until the coil is completely blocked. This will of course reduce heat transfer from the coil to the surrounding air, causing a loss in heating capacity of the heat pump.

Answer 174

Sling Psychrometer This instrument provides both wet bulb and dry bulb readings that can be used with the Psychrometric Chart to determine the properties of the air just sampled.

Answer 175

So that you can determine when to change the filter-drier. Manufacturers publish tables that specify permissible core pressure drops. When the drop exceeds recommendations the core should be replaced.

Answer 176

A sliding valve

Answer 177

Wye-delta starters. Wye-delta starters connect the motor in a wye arrangement during startup. This limits starting current to about one third that of what it would be if the windings were connected in the delta configuration at startup. Once the motor has accelerated, the wiring configuration is switched to delta, and the motor continues to run under full voltage.

Answer 178

Bourdon tube

Answer 179

Resistance

Answer 180

Thermal Mass

Answer 181

Significantly larger than

Answer 182

Relative efficiency of a heating or cooling appliance

Answer 183

Seasonal energy efficiency ratio (SEER)

Answer 184

Uses the total output of a system and the total electrical power used by a system over an entire heating season

Answer 185

Refuse the offer politely and if it happens again notify your supervisor of the situation In this situation it is important to politely tell the customer “No you would not be interested”.

Answer 186

Request authorization from the customer to stay on the job until it is finished that evening In a situation where there is a critical application where there could be potential for monetary losses it is important that the repairs be completed as quickly as possible. With that in mind a request should be made to continue working until the system is repaired and operational.

Answer 187

Body language Body language or motions and gestures during personal communication can speak volumes. Body language often communicates more than spoken words.

Answer 188

Actively listen What you say to the customer is very important but just as important is what the customer has to say to you. Listen to your customer and reiterate at the conclusion of your conversations to be certain all points are clear and understood.

Answer 189

A. Partially Correct: Clean and neat personal appearance B. Partially Correct: Clean and neat service vehicle (inside and outside) C. Partially Correct: Maintaining a clean and organized work site D. Correct: All of the above An HVAC technician is a professional and should always present himself as professional. Part of the professional image includes; clean and neat personal appearance, clean and neat service vehicle, and maintaining an organized work space.

Answer 190

Call the customer to keep them informed of your delay Most customers recognize service companies/technicians are very busy people and that scheduled appointments sometimes get delayed. However, the customer is likely just as busy and may even have to take time off from work to meet you. Whenever you discover that you cannot meet for a scheduled customer appointment at least be courteous and professional and give the customer a phone call so they are not “left hanging”. They may not be happy that you have canceled or postponed but it is far better than not making contact at all.

Answer 191

A. Partially Correct: Criminal records B. Partially Correct: Credit reports C. Partially Correct: Drug testing D. Correct: All of the above Background checks can identify all of the above character faults. In today’s world background checks are part of life we all must get used to.

Answer 192

A. Partially Correct: Work uniform with company logo B. Partially Correct: Being punctual C. Partially Correct: Use of good people skills D. Correct: All of the above Professionalism is boundless, all of the above are indicative of professionals

Answer 193

A. Partially Correct: To reference details at a later date B. Partially Correct: To identify warranty parts or service C. Partially Correct: To provide service details in written communication form D. Correct: All of the above For all parties concerned complete and accurate documentation should be completed on all invoices.

Answer 194

Original supplier of equipment Date of repair, actual labor and the total cost are all very important to have listed on the invoice. The identification of the equipment supplier is not necessary.

Answer 195

A. Partially Correct: Write legibly B. Partially Correct: Do not rush C. Partially Correct: Explain the work order to the customer and ask if they have any questions D. Correct: All of the above All of the above will help to assure completeness of invoices. Writing legibly helps yourself to double check your own documents as well as the customer will be able to understand what you have written and service you have performed. Further, a well written, clear, concise and legibly written invoice is a display of professionalism.

Answer 196

Shim under the high foot with shim stock equal to a reading on the indicator. The indicator is set up to read any movement as a mounting bolt is loosened. If losing the bolt allows a foot to rise up, there is a soft foot condition, and shims must be added below the foot before the bolt is retightened.

Answer 197

Parallel and angular. Shafts must be aligned so that the centerlines meet each other exactly in the center (parallel to one another, or axially), and they must be aligned so that they have no angular difference between them (also called radical alignment).

Answer 198

Drawing Interpretation and Plan Reading Chapter 5 Interpretation of Isometric Drawings

Answer 199

Drawing Interpretation and Plan Reading | Chapter 4 Interpretation of Technical Diagrams and Piping Drawings

Answer 200

Figure 3-2 | ANS: Cap Screwed 45° Elbow - 90° Elbow —

Answer 201

Locate the disconnect switch. One of the first things service mechanics should do when going on a job is to locate the disconnect switches. Then they must be certain to pull the appropriate switch if they are going to work on the equipment. However, the proper procedure is to first stop the equipment, if running, using such controls as will cause the motor controller to stop the motor, and then pull the disconnection. Likewise, equipment should be started by first determining that the motor controller is in the off position, then closing the disconnect switch, and finally starting the motor by means of its controller

Answer 202

Heat pumps

Answer 203

Garbage disposals

Answer 204

Central air conditioning

Answer 205

Utilization

Answer 206

Federal Trade Commission

Answer 207

Economizers

Answer 208

Minimum efficiency reporting

Answer 209

Passive cooling

Answer 210

Solid, liquid

Answer 211

Compressor, condenser, evaporator, & metering device

Answer 212

Heat is removed from it. Refrigeration is the transfer of heat from one place to another by a change in state of a liquid. Cold or coldness is an absence of heat, just as darkness is an absence of light or quietness is an absence of sound.

Answer 213

Radiation Radiation is the transfer of heat by waves, just as light is transmitted by waves. Heat from the sun can be considered a method of radiation. A hand placed near hot stove or fireplace is quickly heated by radiation. There is little heat flow due to radiation unless the radiating object has a high temperature.

Answer 214

Connecting two or more capacitors in parallel When selecting a capacitor for a specific application, a capacitor of the exact capacitance is not always available. However, correct capacitance can be obtained by using certain capacitors in series or parallel. Two capacitors in parallel: Total MFD = MFD, Capacitor 1 + MFD, Capacitor 2 Three capacitors in parallel: Total MFD = MFD, Capacitor 1 + MFD, Capacitor 2 + MFD Capacitor 3 If more than three capacitors are used in parallel, the total MFD is the sum of the MFD ratings of all capacitors, just as in the above formulas.

Answer 215

Any two leads The rotation of a three-phase motor can be reversed by interchanging any two leads because this changes the order of phase rotation and so changes the direction of the rotation of the field.

Answer 216

122.2 | Ohms Law R=E divided by 1 110 divided by 0.9 = 122.2 ohms

Answer 217

Overload protection The starter is the same as the contactor, except for the addition of the overload relays and their wiring connections.

Answer 218

Draws power from only one phase Three-phase motors are subject to another cause of excessive current and heat, in the event that one phase fails. In this case the motor will be said to single-phase, meaning that its entire power supply is derived from one phase. You should note that in a three-phase system, failure of one phase does not leave two phases remaining, but leaves only one phase. When a motor single-phases, the current will increase theoretically 1.732 times. Actually, due to increased impedance drop, the current increase will be approximately 1 1/2 times the normal three-phase current. The assumption is that the motor is able to run on single-phase. If the motor is trying to start, or is running under a heavy load when the single-phase condition occurs, it could fail to start, or it could stop running and draw locked-rotor current.

Answer 219

The difference in the refrigerant boiling temperature and the leaving-water temperature The design water temperatures are typically 55 degrees F inlet water and 45 degrees outlet water for a two-pass chiller. The refrigerant is absorbing heat from the water so it is typically about 7 degrees colder than the leaving water. This is called approach temperature. The approach temperature is very important to the technician for troubleshooting chiller performance. The approach temperature is different for chillers with a different number of passes.

Answer 220

Absorbing heat from the water passing through it A chiller refrigerates circulating water. As the water passes through the evaporator section of the machine, the temperature of the water is lowered. It is then circulated throughout the building where it picks up heat. The typical design temperature for circulating chilled water system are 45 degrees F water furnished to the building and 55 degree F water returned to the chiller from the building. The heat from the building adds 10 degrees F to the water that returns to the chiller. Here the heat is removed and the water is recirculated.

Answer 221

Condenser approach temperature will be 10 degrees The condenser, like the evaporator, has an approach relationship between the refrigerant condensing temperature and the leaving-water temperature. Most water-cooled condensers are two-pass condensers and are designed for 85 degree F entering and 95 degree F leaving water temperature with a condensing temperature of about 105 degrees F. This is an approach temperature of 10 degrees F and is important to the technician.

Answer 222

Water boxes Flooded chillers use much more refrigerant charge than direct expansion chillers so leak monitoring must be part of regular maintenance with high pressure systems. When the water is introduced into the end of the chiller, the water is contained in water boxes. When these water boxes have removable covers known as marine water boxes. When the piping is attached to the cover, the piping must be removed to remove the water box cover and these are known as standard covers. The water box also is used to direct the water for different applications.

Answer 223

Cross The operating characteristics of cross charge inherently reduce hunting. Cross-charged expansion valves are used on applications from +50 degrees F to -100 degrees F particularly where repetitive pull down cycles are encountered.

Answer 224

Allow condensate to drain after the steam has been shut off. Once the steam supply has been shut off, steam will condense and will be unable to drain because of the vacuum. The vacuum breaker provides a vent and allows the condensate to drain.

Answer 225

Pigtail Pipe siphon (pigtail). A pipe siphon forms a water seal that prevents raw steam from entering a gage or control and damaging it. A gage cock or gate valve should be installed between a gage which is installed on a boiler and the pigtail so the gage or pipe siphon can be serviced.

Answer 226

Equalizing line

Answer 227

Equalizing line Equalizing Line (Balance Pipe). A pipe which connects the steam header to the boiler return connection. Drains the condensate from the steam header to the boiler return connection. Drains the condensate from the steam header and returns it to the boiler below the water line. Equalizes the supply pressure in the return line to the boiler. This prevents the boiler water from flowing out of the boiler into the return main.

Answer 228

Air vent Air vent. The air vents that are used in steam systems are temperatureactuated devices which allow air to escape from the system piping while keeping steam in.

Answer 229

Air vent When installed in a one-pipe steam system radiator valves must be fully open or completely closed. If a radiator is overheating the only way to control steam flow is by regulating the rate at which air is eliminated. The radiators closet to the boiler will heat up quickly, the units that are furthest away slowly. Air vents with the smallest air venting capacity should be installed on radiators that are closet to the boiler. This will slow down the steam flow into the radiator. Naturally air vents with the largest air venting capacity should be installed on the radiators furthest away. By installing correctly sized air vents on each radiator, a one-pipe steam heating system can be balanced so that all radiators heat evenly and quickly.

Answer 230

28 inches There are no pumps in a gravity return steam system. At the end of the steam supply main a drip connection, which is often called the "A" dimension must be installed. A drip connection is just a piece of pipe which is installed vertically at the end of the last steam carrying main. The drip connection provides space for the condensate to collect. You should know, from the Basic Science, that the pressure at the bottom of a column of water is 2.31' (70.41 cm) or approximately 28" (71.12 cm) high is 1 psig (6.90 kPa). When the condensate level stacks up high enough in the drip connection to overcome system pressure drop and the resistance in the wet return, the condensate will flow into the boiler. It is standard practice for a system designed for 1/2 psig (3.45 kPa) pressure drop to make the minimum distance for dimension "A" not less than 28" (71.12 cm) above the boiler water line.

Answer 231

In a tee at the end of the last steam carrying main. The tee for the main vent(s) should be placed 15" to 18" (38.1 cm to 45.72 cm) from the end of the last steam carrying main, and at the location a 6" to 10" (15.24 cm to 25.4 cm) long pipe nipple should be installed between the top of the tee and the main vent. By locating the main vent 15" to 18" (38.1 cm to 45.72 cm) from the end of the line it will be protected from water hammer.

Answer 232

Waterlogged The disadvantages of a balanced pressure steam trap are: 1. Flexible bellows can be damaged by water hammer. 2. In order for the trap to open the condensate in the trap must cool below the boiling/condensing temperature at the given pressure inside the trap. This will likely result in condensate backing up into the equipment. This is why thermostatic steam traps are not recommended when water logging of the steam space would create a problem. If a thermostatic steam trap is used for this purpose a cooling leg at least 5' (1.52 m) long should be installed before the trap. The condensate will back up and cool down in the cooling leg, not in the steam space of the equipment. 3. Most balanced pressure type thermostatic steam traps are not recommended for use on superheated steam systems. Because of their size and cost, thermostatic steam traps are usually installed on steam radiators. They are often referred to as radiator traps.

Answer 233

Discharge steam continually The advantages of a float and thermostatic trap are: 1. Because of their thermostatic element, float and thermostatic traps offer excellent air venting capability. 2. Condensate is discharged on a continual basis. 3. It handles light or heavy condensate loads equally well. 4. Trap operation is not negatively affected by pressure fluctuations.

Answer 234

Thermostatic The disadvantages of a balanced pressure steam trap are: 1. Flexible bellows can be damaged by water hammer. 2. In order for the trap to open the condensate in the trap must cool below the boiling/condensing temperature at the given pressure inside the trap. This will likely result in condensate backing up into the equipment. This is why thermostatic steam traps are not recommended when water logging of the steam space would create a problem. If a thermostatic steam trap is used for this purpose a cooling leg at least 5' (1.52 m) long should be installed before the trap. The condensate will back up and cool down in the cooling leg, not in the steam space of the equipment. 3. Most balanced pressure type thermostatic steam traps are not recommended for use on superheated steam systems. Because of their size and cost, thermostatic steam traps are usually installed on steam radiators. They are often referred to as radiator traps.

Answer 235

Steam trap The major drawback of one-pipe steam systems is the ability to control the flow of steam into the heat transfer units. The radiator valve cannot be throttled, it must be fully open or completely closed. The development of the steam trap increased the popularity of two-pipe steam heating systems. When separate steam supply and condensate return lines are piped to each radiator, steam flow into the radiator can be controlled.

Answer 236

High condition in the receiver If a condensate receiver is used to supply water to a boiler the pump will not react to a low water condition in the boiler. The boiler could be dangerously low on water and the condensate receiver pump(s) will not deliver water until the water level in the receiver is high enough to close the electrical contacts and energize the pump(s).

Answer 237

Plug cock A plug valve is needed to regulate the pumps discharge pressure. Most two-pipe gravity return and mechanical return systems that employ boiler feed pumps and condensate receivers to return water to the boiler steam are designed to operate at 2 psig (13.79 kPa). If condensate is pumped into the boiler at 20 psig (137.92 kPa), the water will scream through the short run of pipe, create turbulence in the boiler and cause the check valve to chatter. In this case the plug valve would be partially closed, so the pump(s) discharge pressure entering the boiler is 7 psig (48.27 kPA). The operating pressure is 2 psig (13.79 kPa) and the additional pressure needed to overcome resistance in the piping would be 5 psig (34.48 kPa).

Answer 238

Vacuum switch Vacuum switch. Actuates the pump; it senses the pressure at the end of the vacuum return main. Typically, it cycles the pump on at 3 and shuts it off when the vacuum is pulled down to 8" (20.32 cm) of mercury thus maintaining a pressure of about 5 1/2" (13.97 cm) of mercury in the return main.

Answer 239

Lift fitting Lift fittings. If it is necessary to elevate condensate in a vacuum system, a condensate receiver should be installed. In order to maintain a negative pressure the condensate receiver vent is tied into the vacuum return line. However, condensate receivers are expensive and in an effort to save money lift fittings were often incorporated into many system designs.

Answer 240

Vacuum breaker Vacuum breaker. Is incorporated into the system to protect the vacuum pump from creating too low a vacuum. The pump will be adversely affected if the induced vacuum the pump creates is too low. A vacuum breaker is incorporated into the pump to protect the vacuum pump from creating too low a vacuum. The vacuum breaker will open and let air into the system when the pressure inside the pump drops down to 15"of mercury.

Answer 241

Boiler return trap (gravity) How does a vapor steam heating system work? Every heating unit is equipped with a thermostatic steam trap. If this system is installed in a multistory structure, the bottom of each riser must be trapped. The discharge side of the steam traps is piped into the return piping. The boiler is fired, heat is added to the boiler water and steam is produced. The steam explodes out of the boiler pushing the air and condensate through the steam traps into the return piping. The radiators quickly fill with steam and the call for heat is satisfied. In this system the air flows back towards the boiler and is eliminated from the system by an air eliminator. Some vapor systems utilize vacuum air vents to rid the system of air. Vacuum air vents permit air to leave the system but when the system cycles off air cannot reenter the system through the vacuum air vents. At this point in time air vents that were installed on a one-pipe system often spit out dirty water that would usually wind up on the drapery and carpets. One of the reasons the vapor system became so popular was, if some type of air eliminator was installed at the boiler no radiator vacuum air vents needed to be installed.

Answer 242

Air eliminator In a vapor system, preventing air from reentering the system can control radiator temperature. This can be accomplished by installing thermostatic steam traps or vacuum air vents or an air elimination device. One of the reasons the vapor system became so popular was, if some type of air eliminator was installed at the boiler no radiator vacuum air vents needed to be installed. The purpose of an air eliminator is to remove air from the system rapidly, and at as low a pressure as possible.

Answer 243

Differential controller Differential Controller. Ordinarily a pressure differential of 2" (5.08 cm) is required to assure proper steam circulation in any system. The differential controller is the device that maintains the pressure differential between the supply and return piping in a subatmospheric steam heating system. The controller is factory set to maintain this differential. The differential controller starts and stops the vacuum pump thus maintaining the system differential. For example, if the controller is set to maintain a 2" (5.08 cm) pressure differential and the vacuum in the steam supply piping is at 10" (25.4 cm), the pump will maintain 12" (30.48 cm) of vacuum in the return piping. The preferred location for the differential controller is near the end of the steam main farthest from the control valve, it may, if necessary, be located nearer the vacuum pump.

Answer 244

Decrease Effects of Water Quantity and Temperature on Performance of Water Cooled Condensers The capacity of the condenser will increase whenever the average temperature difference between the refrigerant vapor and the water is increased. If the water quantity is not changed, the temperature difference can be increased by lowering the temperature of the entering water. If it is not possible to obtain colder condenser water, then capacity can be increased by increasing the water quantity. For a given condenser, if water quantity is increased it will increase the water velocity, and so increase the efficiency of heat transfer. However, changes in water quantity have an even greater effect on capacity because of the resulting changes in average temperature difference. Assuming there are no changes in the refrigeration load or in the temperature at which water enters the condenser, if the water quantity is increased, the temperature of the leaving the condenser will be lower, so the average water temperature will be lower. This will result in an increase in temperature difference and a corresponding increase in capacity. On the other hand, if water quantity is reduced, the leaving water will be warmer; the temperature difference will be smaller and the capacity will be reduced.

Answer 245

A. Partially Correct: Air-to-air B. Partially Correct: Water-to-air C. Partially Correct: Water-to-water D. Correct: All of the above Heat pumps may use air or water as the heat source. As applied to air conditioning systems, the two commonly used types of heat pumps are the air to air and the water to air. They may either directly heat the air which is supplied to the space being heated, or they may heat water which then heats the supply air. The four classifications of heat pumps are as follows: Heat Source Medium Being Heated 1. Air - to - Air 2. Air - to - Water 3. Water - to - Air 4. Water - to - Water

Answer 246

Compensates for any pressure drop in the evaporator coil The External Equalizer Superheat is abnormally high and serious loss of evaporator capacity results if the evaporator has any appreciable pressure drop. You might feel that you could compensate for the evaporator pressure by simply adjusting the valve, but this will not give the correct answer because the evaporator pressure drop varies. This pressure drop is due to friction developed when the refrigerant flows through the evaporator, just as friction is developed when a fluid flows through an ordinary pipe. Pressure drop at partial loads will be considerably less than at full load because of the smaller amount of refrigerant flowing at the lighter loads. The variable evaporator pressure drop is corrected for by sensing evaporator pressure, not at the evaporator or valve inlet, but at the evaporator outlet. This is done with a connecting tube called an external equalizer line, and is connected to a suitable fitting on the expansion valve. Such a fitting on an expansion valve should never be capped or plugged. If the valve has an external equalizer connection, an external equalizer line must be installed. The line should be connected to the suction line as close as practical to the bulb; specially, there should be no elbows, or other fittings which increase flow friction, between the equalizer line connection and the bulb. The purpose of the external equalizer line is to be able to sense suction pressure at the point where the bulb is located. In this respect, you should consider that it is possible for some liquid refrigerant to flow from the valve, through the equalizer line into the suction line. Since any liquid will vaporize at that point, the resulting cooling effect could influence the temperature sensed by the bulb. To avoid this, the equalizer line should connect to the suction line at a point a little downstream from the bulb.

Answer 247

It assists the return of the oil to the compressor How must the suction piping be installed? The suction piping must be installed with proper regard for the return of oil to the compressor. If the suction piping rises from the coil outlet, it must be provided with proper oil traps, a trap for each coil section. Traps assist in the return of oil by providing a location in which oil, draining from the evaporator coil, can collect and from which the refrigerant-suction gas can remove it by entrainment. The latter process requires the gas to have significant velocity, but the quantity of gas and its velocity will decrease at reduced loads, very markedly so if the one or more compressors in the system are arranged to provide capacity reduction.

Answer 248

oil The muffler is installed in the discharge line as close as possible to the compressor. Due to their construction, mufflers usually form natural oil traps unless properly installed.

Answer 249

Large fluctuations in system capacity will occur If a system has a large variation in capacity in order to keep the suction riser velocity high a double line may have to be installed. During low refrigerant mass flow rates one of the suction riser traps will fill with oil and the other pipe will maintain enough velocity to maintain oil return to the compressor.

Answer 250

To increase refrigerant velocity to aid in proper oil return As a general rule suction risers line sizes are reduced by one size so that refrigerant velocities can be maintained at acceptable levels to insure proper oil return.

Answer 251

Condenser and the expansion device The receiver is located in the liquid line and is used to store the liquid refrigerant after it leaves the condenser. The liquid receiver is always located after the condenser and before the expansion device.

Answer 252

Suction accumulator The suction-line accumulator can be located in the suction line to prevent liquid refrigerant from passing into the compressor. The suction accumulator is located between the evaporator and the compressor and is used to protect the compressor from liquids entering the compressor.

Answer 253

Solenoid valve The solenoid valve is the most frequently used component to control fluid flow. This valve has a magnetic coil that when energized will lift a plunger into the coil. This valve can be either normally open (NO) or normally closed (NC). The NC valve is closed until energized; then it opens. The NO valve is normally open until energized; then it closes. The plunger is attached to the valve so that the plunger action moves the valve. Solenoid valves are snap-acting valves that open and close very fast with the electrical energy to the coil. They can be used to control either liquid or vapor flow. The solenoid valve is the most frequently used component to control fluid flow in a refrigeration system. It can be designed as a NC or NO valve.

Answer 254

Capillary action Before you heat the joint, it is good practice to introduce nitrogen into the system to purge the air (containing oxygen) and reduce the possibility of oxidation to a minimum. A pressure of 1 to 2 psig is enough to purge the piping. Apply heat to the parts to be joined with an air-acetylene or oxyacetylene torch. Heat tube first, beginning about 1 in. from the edge of the fitting, sweeping the flame around the tube. It is very important to keep the flame in motion and to not overheat any one area. Then switch the flame to the fitting at the base of the cup. Heat uniformly, sweeping the flame from the fitting to the tube. Apply the filler rod or wire at a point where the tube enters the socket. When the proper temperature is reached, the filler metal will flow readily by capillary attraction, into the space between the tube and the fitting. As in soldering, do not heat the rod or wire itself. The temperature of the metal at the joint should be hot enough to melt the filler metal. When the joint is at the correct temperature, it will be cherry red in color. The procedures are the same as with soldering except for the materials used and the higher heat applied. The flux used in the brazing process will cause oxidation. When brazing is done and cooled, wash these joints with soap and water. Capillary action is the process by which the alloy is drawn into the gap between the pipe and the fitting. In order for this to occur there must be enough clearance between the two connections.

Answer 255

A. Partially Correct: CO2 C. Partially Correct: Nitrogen D. Correct: A or C Before you heat the joint, it is good practice to introduce nitrogen into the system to purge the air (containing oxygen) and reduce the possibility of oxidation to a minimum. A pressure of 1 to 2 psig is enough to purge the piping. By purging the atmosphere from the refrigerant piping the potential for copper oxides to be created during the brazing process is eliminated.

Answer 256

Prevent a compressor overload condition. The crankcase pressure (CPR valve) looks the same as the EPR valve, but it has a different function. The CPR valve is in the suction line also, but it is usually located close to the compressor rather than at the evaporator outlet. The CPR valve sensing bellows are on the true compressor suction side of the valve and would normally have a gage port on the evaporator side of the valve. This valve is used to keep the low-temperature compressor from overloading on a hot pull down. A hot pull down would occur (1) when the compressor has been off for a long enough time and the foodstuff has a rise in temperature, (2) on start-up with a warm box, or (3) after a defrost period. In either case the temperature in the refrigerated box or the evaporator influences the suction pressure. When the temperature is high, the suction pressure is high. When the suction pressure goes up, the density of the suction gas goes up. The compressor is a constant-volume pump and does not know when the gas it is pumping is dense enough to create a motor overload.

Answer 257

Prevent a minimum pressure in the regulator The evaporator pressure regulator valve (EPR valve) is a mechanical control that keeps the refrigerant pressure in the evaporator from going below a predetermined point. The EPR valve is installed in the suction line at the evaporator outlet. The bellows in the EPR valve senses evaporator pressure and throttles (modulates) the suction gas to the compressor. This will then allow the evaporator pressure to go as low as the pressure setting on the valve. When the EPR valve is used with the thermostatic expansion valve (TXV), the system now has the characteristics of maintaining a constant superheat and keeping the pressure from going too low.

Answer 258

Green Hose and Connections The hoses used with oxyacetylene equipment are specially manufactured for this service. They must be of ample strength to resist internal pressure, sufficiently flexible to yield readily to the movements of the torch, and nonporous. The oxygen hose is generally black or green in color, and is fitted with special right-hand threaded connections and swivel nuts to attach to the oxygen regulator and oxygen connection to the torch. The color of the acetylene hose is red and is fitted with special left-hand threaded connections (with a groove around the outside) which can be attached to the acetylene regulator and the acetylene valve on the torch.

Answer 259

A. Partially Correct: Soldered B. Partially Correct: Flared C. Partially Correct: Compression D. Correct: All of the above Introduction Depending on the purpose for which it is to be used, copper tube may be joined by a number of methods. The most common method is by soldering with the use of a cup-joint fitting. Solder joints are used for domestic water, sanitary drain lines, hot water heating systems, and other lines where maximum temperatures do not exceed 250 degrees F. Brazed joints, with cup-joint fittings, are used where greater strength is required or where system operating temperatures are as high as 350 degrees F. Brazed joints have limited use for domestic water and drain lines but are sometimes used in steam, hot water heating, refrigeration and specialty applications such as medical gas piping systems. Flared joints are often used for connecting underground lines, for joints where the use of heat is impractical, and for joints that may have to be disconnected periodically. Compression joints, which are made by clamping the tube between threaded parts, are popular for small tube use.

Answer 260

1/2” Air-Conditioning and Refrigeration Tube (ACR) Type ACR copper tube is designated for air-conditioning and refrigeration installations. It is clean, moisture free and capped when it leaves the manufacturer, thus insuring the installer a non-contaminated tube. ACR copper tube differs from the other two classes of copper tube in two major respects: it is available in a greater number of sizes (especially the smaller sizes); and the sizes specified are actual outside diameters. Therefore, its designated size is always 1/8-inch larger than the designated size of copper water and DWV tube with the outside diameter. That is, 1/4-inch copper water tube has the same outside diameter as 3/8-inch ACR tube; 3/8-inch copper water tube has the same outside diameter as 1/2inch ACR tube. Fittings used for ACR tube are the same as the fittings used for water tube. However, care should be exercised in ordering these fittings, because of the different method used in specifying the size of the tube. When ordering fittings of 7/8-inch ACR tube, it is necessary to order 3/4-inch nominal or 7/8-inch O.D., which is the same as required for 3/4inch copper water tube. Example: 1/2-inch copper water tube has the same outside diameter as 5/8inch ACR tube.

Answer 261

As soon as possible Assembly and Support The assembly and support of soldered or brazed piping is an important part of the job. After both tube and fitting surfaces are properly fluxed, they should be assembled, making sure the tube seats against the base of the fitting socket. A slight twisting motion ensures even coverage by the flux. Remove excess flux with a cotton rag. Care must be taken to assure that the tube and fittings are properly supported with a uniform capillary space around the circumference of the joint. Uniformity of capillary space will ensure good filler metal penetration if the guidelines of successful joint making are followed. Excessive joint clearance can cause the filler metal to crack under stress or vibration. The joint is now ready for soldering or for brazing, as the procedures to this point are the same for both processes. Joints prepared and ready for soldering or brazing should be completed the same day and not left unfinished overnight.

Answer 262

Water overflow Condensate Disposal for Cooling Coils. Cooling coils normally condense moisture from the air; the resulting water being collected in a pan from which it is carried away by drain piping. The drain line should have a trap to provide an air seal. Failure to do so can result in inadequate drainage of the pan or in undesirable sucking of air or gases into the conditioned air supply. The trap should have a deep seal, related in depth to the static pressure of the fan, so that fan pressure will not break the water seal, and the trap and the drain line should have adequate cleanouts. The drain line should not be connected directly to a sewer, but may discharge to an indirect or opensight waste or a storm sewer, as required by codes. Drain connections should be on the downstream side of coils, and any baffle along the lower edge of the coils should have weep holes to permit passage, to the drain, of any water collecting on the upstream side of the coil and baffle. When two or more coil sections are stacked one above another, condensate is often carried out into the air stream as it drips from one coil section to the next lower one. In such cases, an intermediate drain pan or trough with drain line can be provided below each upper coil, to conduct condensate directly to the main drain pan.

Answer 263

Carburizing flame Oxyacetylene Flame. The oxyacetylene flame has a peak temperature of about 6300 degrees F, and is known to be the highest temperature oxy-fuel gas flame produced. The highest temperature occurs just off the end of the inner cone of the flame. Two volumes of acetylene combine with two volumes of hydrogen. This expression represents the burning of gases in the inner luminous cone. Just off the end of the cone a temperature of approximately 6300 degrees F is reached. The gases burning in the outer envelope produce 956 Btu for each cubic foot of acetylene originally supplied to the torch. This consideration indicates that two thirds of the heat released by the flame is produced by the outer envelope and only one third of the heat comes from the inner cone. Thus it is seen that in any neutral flame there will be a temperature of approximately 6300 degrees F, but the total amount of heat produced will be dependent upon the size of the flame or, saying it otherwise, upon the number of cubic feet of acetylene burned per hour. An excess of acetylene in the mixture will give a reducing or carburizing flame. This flame is readily recognizable by the secondary luminous envelope around the inner cone and inside the boundary of the outer envelope. With a carburizing flame, the amount of acetylene is adjusted at the torch valve until the secondary luminous cone shrinks to the exact outline of the inner cone, forming the neutral flame. If excess oxygen is added to the acetylene in the mixture, it will produce an oxidizing flame. When more oxygen is supplied to the neutral flame, the inner cone becomes darker and shorter and the whole flame is smaller and hotter. This flame is normally used for brazing certain nonferrous metals. Never adjust an oxy-acetylene flame by reducing the amount of acetylene. This would underfeed the torch causing the flame to burn back into the tip causing overheating and backfire. Once the flame on an oxy-acetylene torch has been adjusted, never cut back on the acetylene after the initial adjustment. Soldering & Brazing UA STAR HVACR Study Guide Revised Apr

Answer 264

Counter-clockwise until the tension is off Pressure adjusting screw. The regulator adjusting screw controls the flow of gas and delivery pressure to the hose and torch. As previously stated, the regulators function to reduce high supply pressures to a suitable working pressure range. When adjusting screw is turned clockwise, the regulator will allow gases to flow through the regulator to the hoses and to the torch. The threaded adjusting screw allows mechanical force to be applied to a spring which controls a flow valve in the regulator. If the adjusting screw is turned counterclockwise, tension on the spring is released and the regulator will not allow the gas to flow.

Answer 265

Greater than that of Type L or Type M Copper Water Tube There are three types of copper water tube ------ K, L and M, each of which represents a series of sizes with different wall thickness. Type K ----- Heavy Wall Type L ----- Medium Wall Type M ---- Light Wall UA STAR HVACR Study Guide Revised April 2

Answer 266

Oxidation and distortion of the joint After the brazed joint has cooled, the flux residue should be removed with a clean cloth, brush or swab using warm water. Remove all flux residue to avoid the risk of the hardened flux temporarily retaining pressure and masking an imperfectly brazed joint. Wrought fittings may be cooled more readily than cast fittings, but all fittings should be allowed to cool naturally before wetting. If the filler metal fails to flow or has a tendency to ball up, it indicates oxidation on the metal surfaces or insufficient heat on the parts to be joined. If tube or fitting start to oxide during heating there is too little flux. If the filler metal does not enter the joint and tends to flow over the outside of either member of the joint, it indicates that one member is overheated or the other is under heated. In either case, the filler metal will flow over the member which is overheated and away from the member that is not sufficiently heated.

Answer 267

Use grease on the hose and regulator threading connections Oil, grease and other easily oxidizable materials must be kept away from oxygen cylinders and valves, and also away from any other oxygen apparatus. A small drop of oil or grease inside an oxygen valve or oxygen regulator can cause an explosion.

Answer 268

A p-trap Problems can occur in getting oil to flow upward in certain vertical piping, and a trap at the bottom of the riser can assist in getting the oil to begin the upward flow. Another purpose of a trap is to prevent oil in certain lines from draining back to the compressor during the off-cycle.

Answer 269

Air conditioning and refrigeration tube Air-Conditioning and Refrigeration Tube (ACR) Type ACR copper tube is designated for air-conditioning and refrigeration installations. It is clean, moisture free and capped when it leaves the manufacturer, thus insuring the installer a non-contaminated tube. ACR copper tube differs from the other two classes of copper tube in two major respects: it is available in a greater number of sizes (especially the smaller sizes); and the sizes specified are actual outside diameters. Therefore, its designated size is always 1/8-inch larger than the designated size of copper water and DWV tube with the outside diameter. That is, 1/4inch copper water tube has the same outside diameter as 3/8-inch ACR tube; 3/8-inch copper water tube has the same outside diameter as 1/2-inch ACR tube. Fittings used for ACR tube are the same as the fittings used for water tube. However, care should be exercised in ordering these fittings, because of the different method used in specifying the size of the tube. When ordering fittings of 7/8-inch ACR tube, it is necessary to order 3/4inch nominal or 7/8-inch O.D., which is the same as required for 3/4-inch copper water tube. The wall thickness of hard temper copper ACR tube are the same as that of Type L water tube. The wall thickness of annealed ACR tube are close to, but not exactly the same as that of Type L water tube. Air Conditioning and Refrigeration tube is made according to ASTM Standard B280.

Answer 270

Circulating steam through them Many high-pressure installations require that the steam reach the equipment in a superheated condition. The tubes between the steam drum and the water or mud drum, called the boiler bank, have the largest amount of surface and are in the boiler proper. They transfer most of their heat by convection as the hot gases pass between them. When it is desired to have a drier and higher temperature steam, the steam from the main steam drum is passed through tubes located in either the main furnace area or in the gas passage area and to the outlet header. These tubes are called the superheaters and transfer heat by both radiation and convection depending upon their location.

Answer 271

Waterwalls As boilers increased in size, the demand for more efficient heat transfer increased. Waterwalls in the furnace, that part of the boiler where combustion takes place, and other changes in design were introduced. The elimination of one or more boiler drums were also a major design change. Two-drum boilers, even boilers with one drum at the top and one or more large headers at the bottom, became common. Five advantages of waterwall boiler design. 1. Increased refractory life 2. Increased steam production 3. Smaller furnace volume per unit of output 4. Increased firing rate per unit of furnace volume 5. Higher heat release in furnace area

Answer 272

Temperature is increased with no increase in pressure Steam, at any given pressure, which is heated above the corresponding saturation temperature with no increase in pressure, is referred to as superheated steam. Only steam that is not in contact with water can be superheated.

Answer 273

Vacuum pump The variable vacuum pump discharges condensate to the boiler or boiler feed pump. When the vacuum pump is in operation and air is being exhausted from the heating system, a pressure differential is established. This in turn causes steam to flow from the steam supply main allowing air and condensate to be returned to the vacuum pump.

Answer 274

Control valve Control valve. This valve controls the steam pressure on the steam supply side of a sub-atmospheric system. A control valve must be installed in a horizontal main and never in a vertical pipe. There should be at least 10' (3.05 m) of straight pipe beyond the control valve. A compound gage with a pipe siphon should be installed about 10' (3.05 m) from the control valve. A pressure of 2 to 10 psig (13.79 to 68.96 kPa) (preferably) should be maintained ahead of the control valve at all times while the system is in operation. The valve is positioned and operated be either a low voltage electric motor, a pneumatic relay, or a combination pneumatic-electric relay according to the temperature readings at the window selector and room thermostat, as corrected by the heat balancer.

Answer 275

28 inches for each pound of pressure the boiler is producing The major drawback of a two-pipe gravity return steam system is getting the returning condensate back to into the boiler. In order to return water to the boiler in a one-pipe gravity return steam heating system a 28" (71.12 cm) "A" dimension is a drip leg located at the end of a steam supply or dry return mains. It provides space so condensate can accumulate and build up and create pressure. Along with the leftover pressure at the end of the main(s), about 1 1/2 psig (10.34 kPa), the pressure which is created in the drip leg will push the condensate back into the boiler. All this changes with a two-pipe gravity return steam heating system. When the steam traps cycle closed, there is no left over steam pressure to help push the condensate back into the boiler. With no left over steam pressure, the length of the drip leg must be 30" (76.2 cm) long for each pound of pressure the boiler produces. Remember, the pressure at the bottom of a column of water 28" (71.12 cm) high is one psig. The extra two inches are needed to overcome friction in the return piping. So, if the pressuretrol were set to shut the boiler off when the pressure reached 2 psig 913.79 kPa), the length of the drip leg would have to be 60" (152.4 cm) long. Quite often it is impossible to achieve the space needed to maintain the necessary distance required to return condensate back to a boiler.

Answer 276

A low water condition in the boiler The receiver must be supplied with make-up water to insure there is water in the receiver to supply water to the boiler. The make-up water to the receiver can be supplied using an electric solenoid or an electric motoroperated valve. This valve is controlled by a float switch in the receiver to maintain the proper level of make-up water and condensate in the receiver. Normally, the electric motor-operated valve or solenoid valve arrangement is used where large quantities of make-up water must be provided. If the receiver make-up water feeder is activated in order to supply water to the boiler, the likelihood of excess water and a flooded boiler or flooded receiver exist.

Answer 277

Removed from boiler tubes for better heat transfer Soot deposits reduce heat transfer rates on the heating surfaces and consequently reduce boiler efficiency, and increase metal surface deterioration.

Answer 278

Flexible bellows Balanced pressure thermostatic steam trap. Located inside this trap is a corrugated metal bellows. Inside the bellows is an alcohol, distilled water or an alcohol/water mixture. All of the substances listed above boil at a lower temperature than water. When the system is off the trap is in the open position. Where there is a call for steam, steam begins to circulate pushing the air in the piping through the steam traps. After the air has been eliminated, cool condensate flows into the trap. As the condensate entering the trap becomes hotter the liquid inside the bellows boils, filling the bellows with vapor. When filled with vapor, the bellows expands forcing the valve onto the seat closing the trap. When the condensate inside the trap cools below the boiling/condensing temperature of the vapor inside of the bellows, the vapor condenses, the bellows contracts lifting the valve off the seat opening the trap.

Answer 279

Condensate Float and thermostatic trap. When condensate enters the trap the water level rises lifting the float and opening the valve. Conversely, when the water level is lowered, the float falls closing the valve. Condensate is discharged from the trap almost as is enters, regardless of its temperature

Answer 280

Water hammer Condensate must be removed as quickly as possible from heat transfer units. If it is not removed quickly the units will fill with condensate and there will be no heat transfer. The steam coming in contact with the trapped condensate will create water hammer.

Answer 281

Hermostatic traps Because of their size and cost, thermostatic steam traps are usually installed on steam radiators. They are often referred to as radiator traps.

Answer 282

Faulty steam trap A steam trap is an automatic device which permits condensate, air and any non-condensable gases to flow out of heating units or steam piping into the condensate return piping without allowing live steam to escape. The basic functions of steam traps are to: 1. Prevent the loss of steam and maintain the pressure differential between the supply and return sides of a steam system. 2. Allow the passage of condensate, air, and other non-condensable gases from the steam supply to the condensate return portion of a steam system. The flow of steam through steam supply piping is maintained by the pressure differential between the supply and return piping. Steam traps are the dividing point between steam supply and condensate return piping. If the pressure differential is not maintained no steam will circulate through the system piping.

Answer 283

Negative gauge pressure A vacuum breaker is designed to prevent the pressure in the condensate return from dropping too low. If system pressure drops below 15 in. Hg, the breaker opens and lets air into the system. Since the pump draws from a tank that is vented to the atmosphere (to allow air to escape), it will typically see atmospheric pressure at the inlet and will be unaffected by system pressure.

Answer 284

Operate by the system duct air pressure System powered controls. System powered controls use the duct pressure in the inlet of the terminal unit as the source of control power.

Answer 285

Achieve maximum sensible cooling without latent cooling The water system has two portions, indicated as primary water circuit and a secondary water circuit. Water in the primary circuit comes directly from the water chilling machines and is the coldest water in the system. Water in the secondary circuit is considerably warmer, consisting of a mixture of primary water, leaving the primary cooling coils and some water recirculated within the secondary circuit. Since one of the features of the system is to perform all necessary dehumidification in the central air apparatus, the primary air must usually be cooled to approximately 50 degrees DB or less, and this requires very cold chilled water.

Answer 286

A source of dehumidified primary air The water system has two portions, indicated as primary water circuit and a secondary water circuit. Water in the primary circuit comes directly from the water chilling machines and is the coldest water in the system. Water in the secondary circuit is considerably warmer, consisting of a mixture of primary water, leaving the primary cooling coils and some water recirculated within the secondary circuit. Since one of the features of the system is to perform all necessary dehumidification in the central air apparatus, the primary air must usually be cooled to approximately 50 degrees DB or less, and this requires very cold chilled water.

Answer 287

Require a changeover control to reverse the action of the fan coil thermostat For year-round air conditioning the two-pipe system must be a dualtemperature system, supplying cold water for cooling and hot water for heating. At some point, as governed by outdoor temperature, there must be a changeover so the system supplies cold water rather than hot-water, or vice versa. The changeover is done at the central plant where the water is heated or chilled. If the units are equipped with automatic valves for thermostatic control of room temperature, the room thermostats must also be changed-over at the same time.

Answer 288

Slot diffuser The success of VAV systems is the development of air diffusers which will perform satisfactorily with reduced air volumes so that air will not simply spill to the floor, but will continue to be evenly distributed about the room, without drafts. The velocity of the air stream leaving an outlet must be high enough to provide the required throw. As air volume is reduced in the variable air volume system, outlet velocity is correspondingly decreased, and this can easily result in lack of throw, excessive drop and drafts. Further, when an outlet discharges air along a flat surface such as a wall or a ceiling, the air stream tends to be held to the surface, this being referred to as a surface effect. Side wall grilles have comparatively little surface effect, ceiling diffusers have more, and slot diffusers have considerably more, especially when the diffuser is quite long as compared to the width of the slot. Diffusers for variable air volume systems are of the slot or linear type, and because of the importance of diffuser selection, manufacturers of variable air volume control devices also offer suitable diffuser terminal units.

Answer 289

Maintain evaporator load. A hot-gas bypass valve is adjusted to maintain a minimum evaporator pressure which prevent the evaporator from forming ice. The valve allows the compressor to operate when the evaporator load falls below the minimum capacity of the compressor.

Answer 290

There is gas in the liquid. The sight glass in a refrigeration system permits a view of the refrigerant at the sight glass location. Installed in a liquid line, the sight glass will show bubbling if there is any gas in the liquid refrigerant. If only liquid, without gas, is present, the glass will show clear. It should be cautioned, however, that the glass will also clear if there is only gas or no refrigerant at all present.

Answer 291

The dielectric strength of the motor’s insulation would be greatly reduced. Deep vacuums have the effect of greatly reducing the dielectric strength of hermetic compressor motors insulation. Therefore, a hermetic compressor motor should never be energized, no matter how briefly, while it is in a deep vacuum. This would include performing a megohmeter test of the motor’s insulation while it is in a deep vacuum.

Answer 292

In series. | Series wiring de-energizes the load when any one of several safeties trips.

Answer 293

120 degrees There are three electromotive forces differing in phase from each other by 120 degrees.

Answer 294

In both pressure and temperature controllers A bellows will expand or contract as the pressure increases or decreases. It is a very popular pressure-sensing device, and is used in most pressure controllers. A very common application of the Bourdon tube is in pressure gages.

Answer 295

Large motors operating with a heavy load. Large motors use a type of ball bearing called a roller bearing, which has cylindrically shaped rollers instead of balls.

Answer 296

A. Incorrect: Large or small. B. Incorrect: Narrow or wide. C. Correct: A or B. Belt widths are denoted by “A” and “B”. An A width belt must not be used with a B width pulley nor vice versa.

Answer 297

Dial indicator A more complicated coupling is used between the motor and a larger pump or a compressor. This coupling and shaft must be in very close alignment, or vibration will occur. The alignment must be checked to see that the motor shaft is parallel with the compressor or pump shaft. Alignment is a very precise operation and is done by experienced technicians, using a dial indicator.

Answer 298

Worn pulley grooves. Belts and pulleys wear like any moving or sliding surface. When a pulley begins to wear, the surface roughens and wears out the belts. Normal pulley wear is caused by use or running time. Belt slippage will cause premature wear. Pulleys must be inspected occasionally.

Answer 299

Corrects minor misalignment. Rigid-base-mount motors are similar to cradle-mount motors except that the base is fastened to the motor body. The sound isolation for this motor is in the belt, if one is used, that drives the prime mover. This motor is often used as a direct drive to turn a compressor or pump. A flexible coupling is used between the motor and prime mover in a direct-drive installation.

Answer 300

Center port of gauge manifold The construction of a typical gage manifold has two shutoff valves and five external connections. The compound gage on the left-hand side is always open to the lower left-hand connection of the manifold, and will indicate suction pressure when connected to the gage port of the compressor suction service valve, or other suitable connection. Similarly, the pressure gage on the right-hand side is always connected to the gage port of the compressor discharge service valve, or equivalent pressure connection. When both manifold valves are closed (front-seated) the center or utility port is isolated, but the opening of either valve opens the center port to that side of the manifold and the refrigeration system. The hose connected to the center port can be attached to a container of refrigerant for charging the system. The center port can also be attached to a container of oil and the manifold used to control the addition of oil to the compressor, or it can be attached to a vacuum pump to evacuate the system.

Answer 301

Throttling the discharge The valve on the suction side of the pump should be fully open. Never throttle flow through the pump with the suction valve. It could cause cavitation. What is cavitation? Cavitation is the flashing of a pumped liquid into vapor bubbles and the subsequent violet collapsing of those bubbles as the liquid moves from suction to discharge through the pump. It can be extremely damaging to the pump internally, as well as to the piping and pump mountings. It can cause the pump to vibrate and shake erratically. Cavitation can cause a sound like gravel passing through the pump. Cavitation can be caused by suction pressure which is too low (insufficient static pressure in the system) or by excessive flow through the pump (which can be corrected by throttling the discharge valve) or by the fluid being too hot. If cavitation cannot be corrected quickly, the pump should be turned off to prevent damage.

Answer 302

Outlet pressure will be reduced The regulator vent is an essential part of regulator operation. What is the purpose of the regulator vent? The regulator vent allows the air above the diaphragm to escape or enter as the diaphragm moves up or down. Blockage of the vent would cause the air above the diaphragm to become locked in, and prevent the free movement of the diaphragm. If the diaphragm should rupture allowing gas above the diaphragm, the vent allows this gas to escape into the atmosphere, rather than cause an unsafe operating condition. Most small regulators vent into the atmosphere but gas codes restrict the size of the vent opening. Larger regulators may pipe the vent opening to the combustion chamber beside a constant pilot flame or to the outdoors. Check state, local or provincial codes.

Answer 303

Type of ignition system You must take into account certain factors relating to the piping system before you can select a regulator for a particular application. Which factors must be considered when selecting a regulator? 1. Rate of flow the regulator will be required to supply (usually in cubic feet per hour) 2. Type of gas (natural or propane) 3. Inlet gas pressure to the regulator (minimum and maximum) 4. Outlet gas pressure of the regulator 5. Size of gas pipe at the regulator

Answer 304

Faulty steam trap A steam trap is an automatic device which permits condensate, air and any non-condensable gases to flow out of heating units or steam piping into the condensate return piping without allowing live steam to escape. The basic functions of steam traps are to: 1. Prevent the loss of steam and maintain the pressure differential between the supply and return sides of a steam system. 2. Allow the passage of condensate, air, and other non-condensable gases from the steam supply to the condensate return portion of a steam system. The flow of steam through steam supply piping is maintained by the pressure differential between the supply and return piping. Steam traps are the dividing point between steam supply and condensate return piping. If the pressure differential is not maintained no steam will circulate through the system piping.

Answer 305

The desired concentration of total dissolved solids Cooling Tower drift is water lost from the tower due to drift, or carry-over of a water mist or water droplets due to being blown through the eliminators. The proper location of a cooling tower bleed-off is: at the high point of the condenser water piping. This is important; otherwise the bleed-off line will act as a drain and cause an unnecessary waste of water when the system is off.

Answer 306

Fewer The run winding is wound with a large diameter wire than the start winding and have fewer turns.

Answer 307

75% When the motor reaches approximately 75% of its normal speed the start winding is removed from the circuit.

Answer 308

A capacitor The start capacitor is wired in series with the start windings to give the motor more starting torque. The capacitor is chosen to make the phase angle such that is most efficient for starting the motor.

Answer 309

A. Partially Correct: Start windings B. Partially Correct: A start capacitor C. Partially Correct: A start relay D. Correct: All of the above Three phase motors have no starting windings, capacitors, or relays. They can be thought of as having three separate single phase power supplies.

Answer 310

Capacitor | All capacitors are rated in microfarads.

Answer 311

It will be lower than it should be The voltage of an installation is important because every motor operates within a specified voltage range, usually within + or- 10%. If the voltage is too low, the motor will draw a high current. For Example, if a motor is designed to operate on 230V but the supply voltage is really 200V, the motor’s current draw will go up. The motor is trying to do its job, but it lacks the power, and it will overheat. If the applied voltage is too high, the motor may develop local hot spots within its windings, but it will not experience high amperage. The high voltage will actually give the motor more power than it can use. A 1-hp motor with a voltage rating of 230V that is operating at 260V is running above its 10% maximum. The motor may be able to develop 1 1/4 hp at this higher-than-rated voltage, but the windings are not designed to operate at that level. The motor can overheat and eventually burn out if it continually runs overloaded. This can happen without drawing excessive current.

Answer 312

Run-load amperage Run load amperage is also referred to as the full load amperage and is the current drawn while the motor is running at full load.

Answer 313

Capacitor The safest way to discharge a capacitor is by using a 20,000-ohm, 5 watt resistor.

Answer 314

1/5 that of a full-load amperage Normally the Locked-Rotor-Amperage of a motor is about six times the Run-Load-Amperage.

Answer 315

A pilot duty relay | Pilot duty relays can switch larger contactors or starter on or off.

Answer 316

A contactor A contactor is a larger version of a relay and can be rebuilt. The magnetic holding coil can be designed for various operating voltages.

Answer 317

A motor starter | A motor starter is similar to a contactor but also includes overload protections.

Answer 318

A thermal device buried in the motor windings If a motor is designed with an internal overload the device will be buried in the motor windings and open if the temperature exceeds a predetermined limit.

Answer 319

A. Partially Correct: A line fuse B. Partially Correct: A circuit breaker C. Partially Correct: Magnetic overload D. Correct: All of the above Any of the items above could be used to protect a motor from over current, however the magnetic overload would also protect against over current independent of the ambient temperatures.

Answer 320

The start winding has an open somewhere On any circuit that is open an ohmmeter will have an infinite reading.

Answer 321

Three Phase The direction of a three phase motor can be changed by reversing any two legs of the circuit. The direction of the other types of single phase motors cannot be changed externally.

Answer 322

Start windings Since each of the induction motor’s stator windings are 120° out of phase, it will generate both good start-up and run torques.

Answer 323

A small pole of thick copper wire Shaded pole motors can easily be identified by the heavy gauge copper band located around the stator of the motor.

Answer 324

A. Partially Correct: When low start torque is required B. Partially Correct: When low run torque is required Shaded pole motors are very common throughout the industry and are used in low torque applications.

Answer 325

Capacitor-run Capacitor-Run motors provide a moderate torque while maintaining good running efficiency. The capacitor start capacitor run motor is less efficient. The three phase motor is high torque.

Star Exam 2.0 Flashcards

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