UA HVAC Star Mastery Flashcards
(169 cards)
1
Q
For applications where quiet operation and light axial load characteristics are found, the type of bearing normally used is the ________.
A
Sleeve Bearing
Sleeve bearings are reliable bearings 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.
2
Q
Sleeve bearings with an oil port lubrication system must be lubricated with the proper oil because________.
A
A. Oil that is too thin, will allow the shaft to run against the bearing surface.
B. Oil that is too thick will not run into the clearance between the shaft and the bearing surface.
C. The correct oil allows the motor shaft to float on a film of oil between the shaft and the bearing surface.
D. All of the above
3
Q
Too much grease in a grease lubricated ball bearing ______.
A
Causes Overheating
The most common cause of overheating in a ball bearing is excess grease.
4
Q
The maximum desirable operating temperature of a ball bearing is _______.
A
180°F
A bearing hotter than 180°F is an indication of possible trouble. Infrared thermometers can be used to quickly check for hot bearings.
5
Q
Shaft run out can be measured with ________.
A
A dial indicator and a runout gage
6
Q
The seal in a compressor is necessary to prevent ________.
A
Refrigerant and oil from leaking out at the rotating shaft
7
Q
The mating seal surfaces on a sleeve type rotary bellows seal are ________.
A
Polished steel surfaces, and a carbon ring
It is the mating surfaces of the steel and carbon ring that formed a seal in this type of seal.
8
Q
A fan with a 14 inch sheave is connected by belts to a motor. Calculate the fan speed if the motor is operating at 1725 RPM, and is fitted with a 5 inch sheave. Use the formula below.
A
616 RPM
9
Q
With belt driven equipment, alignment of the motor and driven equipment pulleys _________.
A
** 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.
10
Q
To correct for soft foot, _________.
A
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 loosening 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.
11
Q
The two planes of alignment that must be considered when aligning a flexible coupling are _________.
A
Parallel, and angular
Shafts must be aligned, so that the center lines 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 radial alignment)
12
Q
Electrical pressure is measured in_________.
A
Volts
13
Q
Electricity results from the movement of tiny negatively charged particles called_________.
A
Electrons
14
Q
Use the diagram below to answer the next question.
Calculate the voltage in the circuit when the total amperage is 10 amps and the resistors have values as follows: R1 = 10 ohms, R2 = 15 ohms,
R3 =20 ohms.
A
450 volts
Use ohms law to calculate the value for voltage in this series circuit. Remember that resistance is add up in a series circuit.
Rt= R1+R2+R3
15
Q
Use the diagram below to answer the following question.
Calculate the value for R3 when the value for R1 = 150 ohms, R2 = 500 ohms, the voltage is 120 V, and the amperage is 0.12 amps.
A
350 ohms
Use ohms law to calculate the value for resistance in this series circuit. Remember that ohms law will give total resistance. In this case, the volume for only one resistor is needed.
16
Q
Use the diagram below to answer the next question.
Calculate the voltage in the circuit when the total amperage is 20.4 A and the resistors have values as follows: R1=10 ohms, R2=50 ohms,
R3= 20 ohms.
A
120 volts
Use ohms law to calculate the value for voltage in this parallel circuit. Remember that in parallel circuits, current is additive, resistance is not.
17
Q
What is the maximum safe amperage draw of the secondary winding of a
60VA transformer output of 12 volts?
A
5 amps
Divide VA by volts to obtain the correct answer.
18
Q
The best way to determine the voltage requirements for an electrical component is to_________.
A
Read the nameplate data
19
Q
Fuses can be checked using a _________.
A
An ohm meter or a voltmeter
20
Q
Which of the following devices may be wired into the starting circuit of a single phase motor to improve the starting torque?
A
A start capacitor AND another winding
21
Q
A single phase motor with an improved power factor reduced motor current increased efficiency and high starting torque is the _________.
A
Capacitor start-capacitor run (CSR) motor
Because of the run and start capacitor, this motor offers the advantages listed above. The downside is additional cost.
22
Q
In a CSR motor with a 10 µF run capacitor and a 110 µF start capacitor, the total capacitance will be _________.
A
120 microfarads
The capacitance of capacitors, when wired in parallel as in a CSR motor are added together, the same as resistors in a series circuit.
23
Q
The instrument used for finding humidity levels in the atmosphere is a _________.
A
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.
24
Q
For reading the lowest vacuum levels, the best instrument to use is _________.
A
Electronic vacuum gauge
Electronic vacuum gauges are sufficiently accurate to measure pressures below 2000 µm.
25
A hermetic motor should never be energized or tested with a megger when in a deep vacuum because _________.
**The dielectric strength of the motors insulation would be greatly reduced.**
Deep vacuums have the effect of greatly reducing the dielectric strength of a 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 Megger test of the motors insulation while it is in a deep vacuum.
26
What reduced voltage starter uses a switching arrangement to connect the windings of three phase motors in different configurations during start up and normal operation?
**Star-delta starters**
Star-delta starters connect the motor in a star (or wye) arrangement during startup, which reduces starting voltage to approximately 58% of line voltage. This limits starting current to about 1/3 that of what it would be if the windings were connected in Delta at start up. Once the motor has accelerated, the wiring configuration is switched to Delta and the motor continues to run under full voltage.
27
According to NEC (National Electrical Code) a general use switch may be used as the controller for a stationary motor rated at 2 hp or less, and at 300 volts or less if it is rated at not less than_________.
**Twice the full-load motor current**
28
Two types of thermal overload relays in common used today are _________.
** The bimetal relay, and the melting alloy relay**
29
A rather common indication of a defective starting relay in a single phase motor is _________.
** The motor will hum but not start**
30
The level of voltage caused by back electromotive force that opens the contacts on a potential relay in order to take the start capacitor out of the circuit is called _________.
**Pick-up voltage**
31
A type of current relay that uses a bimetal strip to open contacts in both the starting and running contacts is called a _________.
**hot-wire relay**
32
A pneumatic timing relay operates by _________.
** Filling a bellows with air**
When energized, a bellows fills with air, which takes time. The time can be adjusted by a needle valve, which regulates the rate at which the bellows fills. When fully expanded, the bellows operates a snap action switch.
33
The combination safety limit and fan control on a residential furnace turns the fan on and off by sensing the furnace air temperature. If the furnace temperature rises too high, the safety limit de-energizes is the_________.
**gas valve**
The gas valve is shut off while the fan is allowed to continue running in order to cool the furnace.
34
Some codes require a manual reset device on a safety limit __________.
** so that the cause of the safety shut down can be investigated prior to restart**
35
In order to protect a load safety limit devices are most often wired _________.
**in series**
Series wiring de-energize the load when any one of several safeties trips.
36
A flow switch safety control is used to_________.
** Prove that flow is occurring**
These switches prove that flow is occurring such as in water piping to hot water boilers to verify that the pumps are operating and water is flowing before the main gas valve is opened or to ensure that water is flowing through chiller barrels before energizing the compressor.
37
What is a disadvantage of the mercury bulb switch?
**They must be level**
In order to operate correctly, the thermostat must be mounted absolutely level.
38
A thermostat is properly calibrated when_________.
**set point in control point are equal**
Oh, setpoint refers to the manual setting of the thermostat while control point refers to the actual temperature of the space. The difference between the two is known as offset. When setpoint in control point are equal offset is zero, and the thermostat is said to be “satisfied”. If the temperature agrees with an accurate thermometer, it’s calibrated.
39
With a change in temperature, a thermistor will change_________.
**resistance**
40
One type of pressure sensing device uses a flattened metal tube which is bent into a part circle with one end fixed in place and connected to a system to be measured. The other end of the tube is closed and free to move. An increase in pressure tends to straighten the tube. The movement of the free end of the tube is connected to a dial that reads pressure. This type of gauge is called a_________.
**Bourbon tube**
41
A pressure sensing device that relies on a fluid such as oil to provide a frictionless seal is the_________.
**inverted bell**
This device is suitable on only very low pressure, such as static pressure in an air duct, where pressures usually do not exceed several inches of water.
42
An advantage of a diaphragm is that it can produce a large force when acted upon by only a small pressure. Calculate the total force exerted by an 8” diaphragm with a pressure of 1.8 psig applied to the diaphragm.
**90.5 pounds**
Force = Area x pressure
Area = π r²
F = π r² x psig
3.14 x 4² x 1.8 = 90.447 = 90.5 pounds
43
The photocell in an infrared sensor is made of _________.
**lead sulfide**
Lead sulfide is a semiconductor having the property of decreasing in electrical resistance when exposed to radiation of certain wave lengths.
44
Aiming of infrared sensors is critical. Why must they be aimed directly at the flame?
** Since they say heat, their sensitivity can be reduced by hot refractory**
The steady glow of a hot refractory will cause some decrease in resistance of the photocell material which reduces the sensitivity of the system. For this reason, the photocell should be installed so that it does not directly “see” the refractory.
45
A type of two position control that provides for “intermediate” positions as well as the “all on” and “all off” positions is the _________.
**floating control**
46
While proportional control action has the disadvantage of control point shift but has no time lag factor, floating action has the disadvantage of time lag influence but has no control point shift. What control action combined the advantages of both?
** Proportional integral**
PI control has no time lag factor and maintains a single control point.
47
A flame sensing strategy that takes advantage of the fact that hot gases in a flame become ionized and conduct, electricity is called a _________.
**flame rod**
Flame rods are designed so that current conducted in the flame is much stronger in one direction (half cycle) than in the other, which produces a rectified signal.
48
Checking amperage on a system during general maintenance _________.
**can indicate a problem in the system**
Amperage readings that are too high or too low can be an indication of electrical, mechanical or refrigerant charge problems with the system.
49
When changing or adding oil to a compressor __________.
** it is best to buy the smallest possible containers and use the entire contents at once avoid pouring the oil from a container into the compressor and use an oil charging pump**
All of the above
50
As the evaporating temperature of any vapor compression system is lowered,_________.
** Compressor capacity is lowered**
51
As a “rule of thumb”, for every 12,000 BTUH of cooling capacity in an open compressor air conditioning system, the heat rejection is roughly _________.
**15,000 BTUH, or 1.25 times the net refrigeration effect**
Like any rule of thumb, this number can vary. However, as a basis for estimation, it has long been considered that the heat rejection from an air conditioning system is about 15,000 BTUH for every 12,000 BTUH of cooling capacity. This assumes open-type compressors, where the refrigerant suction vapor does not receive any heat from the compressor motor as it does in hermetic motor-compressors.
52
The difference in temperature between condensing temperature and entering water or air temperature is known as _________.
**temperature split**
The condensing temperature should be at least 15° or 20° higher than the temperature of the entering water or air to avoid the need for an unreasonably large and costly condenser.
53
A decrease in condensing temperature will _________.
**Decrease condensing pressure, decrease suction, temperature, and increase system capacity**
A decrease in condensing temperature affects the entire system, and will cause a drop in evaporator pressure. The drops in both condensing and evaporator pressures (and temperatures) result in a higher system capacity.
54
Subcooling in the condenser will_________.
**Increase system capacity**
An increase in subcooling will increase the net refrigeration effect by reducing the flash gas loss.
55
Compressor capacity controlled by the cylinder unloading method_________.
** may result in compressor overheating**
As fewer cylinders are used less refrigerant is pumped resulting in less refrigerant vapor available for cooling the compressor.
56
10 in.Hg. Vacuum is approximately equivalent to __________.
**10 psia**
Absolute pressure is zero at a perfect vacuum of approximately 30 in. Hg. Meanwhile, atmospheric pressure is approximately 15 psia while vacuum is 0 in. Hg. The table below shows the relationship. Basically, every unit of five on the psia scale is equal to a unit of 10 on the vacuum scale. As vacuum increases by 10, pressure reduces by 5.
57
After repairing a leak, it is permissible to pressure test a system using nitrogen with a small amount of _________ added as a trace gas.
**HCFC 22**
HCFC may be used as a trace gas when mixed with nitrogen for pressure testing, then vented into the atmosphere as it is not being used as a refrigerant.
58
When charging a system, the refrigerant cylinder pressure may drop to low for further charging. Which of the following methods should *not* be used to increase the pressure?
** Heat the cylinder with a torch**
You should never heat a cylinder with a torch and should never raise the temperature above 125°F.
59
A term used to rate vacuum pumps is used to describe the pumps ability to draw a vacuum. Essentially, the pump must create a vacuum within itself that is lower than in the system, so that gases will flow from the system to the pump. The point at which a pump can no longer create a pressure difference is called __________.
**blank-off pressure**
60
Vacuum pump oil is a special oil because _________.
** it has a low vapor pressure to ensure that it won’t vaporize at low pressures.**
61
Which of the following methods will not decrease the time needed to evacuate a large refrigeration system?
A. Using large diameter fittings
B. Keeping hose lengths as short as possible.
C. Triple evacuation.
D. Using multiple vacuum pumps.
**Triple evacuation**
Triple evacuation is a method that is no longer recommended since it vented refrigerant into the atmosphere. Further, it did not reduce evacuation time at all, but was a method used to dilute any contaminants within the system as much as possible.
62
A danger with leaving a vacuum pump running all night is ___________.
** Exceeding the pumps running time capabilities and pump oil could be lost during a power outage**
63
Vacuum pump oil that is fresh _________.
**has a clear appearance**
New oil has a clean and clear appearance. If it looks otherwise, it should be changed.
64
A refillable refrigerant cylinder must not be filled above ________ percent of its capacity buy weight.
** 80%**
65
A refrigerant with the ANSI/ASHRAE standard 34–1992 safety classification of A1 has__________.
** Low toxicity, and no flame propagation**
66
All appliances containing more than 50 pounds of refrigerant (except commercial and industrial process refrigeration) must be repaired when the annual leak rate exceeds_________.
**15%**
EPA requires that all appliances containing more than 50 pounds of refrigerant except commercial and industrial process refrigeration must be repaired when the annual leak rate exceeds 15% and commercial and industrial process refrigeration must be repaired when the annual leak rate exceeds 35%.
67
When charging a chilled water system charging is usually done as a liquid. However, if the machine is in a deep vacuum, the initial charge should be as a vapor. Why?
** Charging as a vapor until the system temperature has risen above 32°F prevents freezing of water in the tubes**
The system must be charged as a vapor until the system pressure has reached a pressure corresponding to a temperature higher than 32°F.
68
When charging a system, several methods are available for checking the refrigerant charge in order to charge by monitoring the sub cooling one must_________.
** Monitor discharge pressure and liquid line temperature close to the metering device and charge until the liquid line temperature falls below the discharge saturation temperature by the expected amount of subcooling**
69
Insufficient refrigerant will cause_________.
** Low suction, pressure and insufficient cooling**
70
Most compressors are positive displacement machines. Name a compressor that is not a positive displacement machine.
**Centrifugal**
71
The ratio of the actual volume of refrigerant vapor pump to the theoretical displacement, volume is known as_________.
** volumetric efficiency**
72
A compressor in which the compressor and motor are both sealed within the same pressurized housing is known as a_________.
** Hermetic compressor**
73
The passage of liquid refrigerant through the compressor suction and discharge valve should be avoided and is known as_________.
** Slugging the compressor**
74
Modern high-speed, reciprocating compressor is typically operate a_________.
**1750 and 3450 rpm**
75
Compressor capacity decreases as_________.
**Discharge pressure increases, suction pressure decreases, and compressor speed decreases.**
76
And advantage of the scroll compressor is_________.
** Smooth, quiet operation, low torque variation through overlapping compression cycles, and few moving parts**
77
How can you identify reverse operation with a scroll compressor?
** the compressor will not compress, and the compressor will stop on motor overload**
78
During scroll compression_________.
** Refrigerant vapor enters from the outside of the scroll and exits at the center**
79
Capacity control on a helical-rotary (screw) compressor is obtained using_________.
** a sliding valve**
80
The screw type impellers used in helical rotary compressors are also known as_________.
** rotors**
81
The component in a centrifugal compressor that actually does decompressing is known as_________.
** an impeller**
82
A centrifugal compressor controls capacity through the use of_________.
** Variable speed, and vortex dampers**
83
Bearings in a centrifugal compressor can be checked by_________.
**Checking the temperature of the oil returning from the bearing**
A high temperature in the oil indicates a bearing with a large amount of friction, indicating that a problem exists.
84
A small access valve, which is similar to the air valve used on tires is known as a_________.
** Schrader valve**
85
A valve used to prevent flow of liquid, refrigerant to the evaporator and to avoid flood back to the compressor during off cycles is_________.
** solenoid valve**
Solenoid valves have many applications in refrigeration systems, the principal one being to prevent flow of liquid, refrigerant to the evaporator, and to avoid flood back to the compressor during off cycles.
86
Hey special valve used to prevent evaporator temperature from falling below a predetermined minimum temperature regardless of suction pressure is the _________.
** evaporator pressure regulator**
An example of an application for this valve is on systems with multiple evaporator’s operating at different temperatures.
87
A metering device with the characteristic of feeding liquid into the evaporator at the same rate at which the liquid flows from the condenser is the_________.
** High side float valve**
This valve consists of a float and a needle valve, which creates the pressure drop separating the high side from the low side of the system. As the liquid level from the condenser raises, the float raises and opens the needle valve, forcing refrigerant into the evaporator. As the liquid level from the condenser drops, the float drops also and closes the needle valve restricting the flow to the evaporator.
88
In a thermostatic expansion valve, three forces act on the diaphragm in the powerhead, which is connected to the valve. Evaporator pressure acts to_________ the valve, spring pressure acts to_________the valve, and bulb pressure from the bulb attached to the evaporator outlet asked to blank the valve.
**Close; Close; Open**
Both the evaporator pressure and the spring pressure act to close the valve while the suction pressure from the bulb asked to open the valve.
89
The metering device that actually measures temperature rather than pressure or liquid levels_________.
** thermal electric valve**
90
Suction line filter driers should be installed whenever_________.
** a hermetic compressor motor burn out has occurred**
Suction line filter driers should be installed whenever a hermetic compressor motor burn out has occurred to filter out debris and carbon char and to neutralize system acid, which is usually generated.
91
Filter, dryers and dryers are filled with the material that is able to catch and retain moisture and acid. This material is called___________.
**Desiccant**
92
Suction line filter dryers are usually equipped with Gage connections, so that pressure drops can be determined. Why?
**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.
93
In general, the greater number of rows in an evaporator_________.
** The more closely the leaving air temperature will be to that of the refrigerant, the more dehumidification can take place, and the colder the leaving air will be.**
94
Increasing airflow over in evaporator__________.
** increases evaporator capacity**
The more air that flows past in evaporator, the more energy is absorbed by the refrigerant. Using the formula for sensible heat transfer, it can be seen that if the temperature difference between the air and the refrigerant remains the same, an increase in airflow (CFM) will result in an increase of energy transfer (BTUH).
*Btuh* = *cfm* x 1.08 x Δ*T*
95
Capacity control of a lithium bromide water absorption machine is accomplished__________.
**By controlling the heat input to the generator**
More heat results in an increased amount of refrigerant boiled out of the solution in the generator, creating more refrigeration effect. Less heat results in less refrigeration effect.
96
Crystallization may occur in a lithium, bromide water absorption__________.
** if power fails while the machine is under a heavy load, if condenser water is allowed to get too cold, and if the machine over cools during a shut down**
97
The heat source for absorption liquid chillers could be_________.
** solar panels, steam, or hot water**
98
The purge units on absorption liquid chillers are designed to_________.
** expel noncondensible gases**
99
A possible cause for high head pressure is_________.
** dirty condenser tubes, insufficient water flow through the condenser, and air or noncondensibles in the condenser**
100
Approach temperature is the difference_________.
** Condensing temperature and leaving water temperature**
Calculate approach, temperature by subtracting the living water temperature from the condensing temperature.
Example: 105°F condensing temp - 95°F leaving water temp = 10°F approach temperature.
101
Calculate the amount of water needed per ton of refrigeration in a water cooled condenser assuming a heat rejection rate of 15,000 BTUH per ton and a 20°F water temperature rise through the condenser.
**1.5 gpm**
GPM = Btuh ÷ (Δt x 500)
102
What are the three ingredients necessary to start in sustain combustion?
**fuel, oxygen, and heat**
103
What are the products of perfect combustion using oxygen and a hydrocarbon fuel?
**Carbon dioxide, heat, and water**
Perfect combustion produces only heat carbon dioxide and water (in the form of vapor)
104
Describe the appearance of a properly adjusted natural gas flame in an atmospheric burner.
**Steady blue flame with a smaller lighter blue inner cone resting on the burner port**
105
Radiant tubing/piping should be pressure tested to at least ______ times the expected operating pressure.
**2**
106
When filling a radiant heating system, it is recommended to fill__________.
** Slowly from the low point, so that the tendency for air pockets to form is reduced**
The idea is to add the water slowly so that air is “chased” to the top of the system so that air pockets do not form.
107
Infrared heaters use burning gas to heat a specific radiating surface instead of using the infrared energy from the open flame because_______.
** heated surfaces are better heat radiators an open flame**
108
High efficiency (condensing) furnaces achieve an efficiency of up to 95% by_________.
** Cooling the exhaust gases to below dewpoint and recovering some of the latent heat of condensation**
High-efficiency condensing furnaces cool exhaust gases to below 130°F. This temperature is below the dewpoint and gains of an additional 1000 BTU for every pound of water condensed is realized. The exhaust gases are cooled to the point where they will not rise up the vent on their own, so an induced forced draft fan must be added. Further, a drain must be installed to take away the condensed water from the exhaust gases.
109
Calculate the efficiency of a furnace with a 95,000 BTUH input burner that produces 76,000 of usable heat.
**80%**
Efficiency = output ÷ input
110
Safety controls on a high-efficiency condensing furnace include________.
** high limit, flame proving, door switch, and induced draft pressure switch**
In order for a high-efficiency condensing furnace to operate, these for safety devices must be “made”
111
The purpose of a boiler low limit control is to__________.
** Start the boiler, when boiler water temperature drops below a certain value**
The low limit maintains boiler water temperature even when the thermostat is not calling for heat. This feature is necessary when using the boiler to heat domestic hot water.
112
In order for fuel oil, to be burned, it must be itemized. This is done by forcing it through a nozzle under a pressure of__________.
**100 psi**
113
A method of sensing flame in older style fuel oil furnaces and boilers was the stack switch which sensed heat in the stack. This required the fuel to ignite, then heat the stack. A trial for ignition took up to 90 seconds. A newer and quicker safety control that “sees” the bright yellow flame has all but replaced the stack switch in fuel oil burners. What is this photocell safety control?
** a cad cell using cadmium sulfide as the sensor**
Cadmium sulfide is used as a photocell in a visible light detector. It has the property of offering low resistance when exposed to light and high resistance when there is no light. Cad cells work well with a fuel oil flame because it is bright yellow. Natural gas and propane burn with a blue colored flame and do not produce much light so cad cells do not work well with those fuels.
114
The practice of adjusting boiler water temperature so that water temperature is hottest on the coldest days and coolest on warmer days is known as _________.
**Outdoor reset**
115
A compression tank is provided in a hydronic system_________.
** so that higher pressures can be built up, thereby raising the boiling point, so that room is provided for heating water to expand, and to provide a cushion against sudden pressure changes and waterhammer shock.**
116
Expansion joints are needed in hydronic system__________.
** to allow for expansion and contraction of the piping**
Copper tubing expands 1.66” per hundred feet with a 150°F temperature rise. Steel expands 1.17”under the same conditions. Allowances must be made for this movement or leaks will develop and pipes/fittings may crack.
117
In order to reduce water turbulence at the suction end of a pump, a suction diffuser should be used or a length of straight pipe equal to_______ times the diameter of the pipe.
** 5 **
118
Premature bearing we’re on the floor mounted palms could be caused by__________.
** suction, or discharge lines that were forced into position when the pump was installed**
The torque of the pipes on the bearings causes excessive stress and could easily lead to early bearing failure.
119
Hey, stuffing box type of shaft, seal on a centrifugal pump need periodic maintenance. If the seal is found to be leaking excessively, the technician should ________.
** 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 the water acts as a lubricant. If tightening the packing gland does not minimize the leak, the packing itself may be worn and need replacing.
120
Cavitation can destroy a centrifugal pump, is noisy and is caused by________.
** 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.
121
The vacuum pump used in vacuum steam heating systems that creates a vacuum using high velocity water is the__________.
** 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.
122
Vacuum pumps used in vacuum steam heating systems can be destroyed if they are made to pump_________.
** air and steam**
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.
123
If a vacuum pump in a vacuum steam, heating system burns out a very common cause is________.
** 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 vacuum pump failure.
124
The type of pump found in a fuel oil burner is the__________.
** gear pump**
125
A gear pump is a type of__________.
** rotary pump**
126
Effective recovery of condensate reduces the following cost of making steam:
** fuel and energy cost associated with producing steam, boiler water make up and sewage treatment, boiler water chemical treatment.**
127
A symptom of a failed steam trap________.
** a track that is warmer than condensate temperature**
A trap that is warmer than 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.
128
After the first heating season, cleaning a dirt pocket by removing the cap on the bottom of a dirt pocket__________.
** is usually not required**
The dirt pocket should be clean several times during the first heating season to remove heavy foreign materials such as scale and pipe cuttings. Thereafter, such attention is usually not required.
129
The average house line pressure for natural gas is_________.
**7” W.C.**
130
The pressure is measured on a residential gas regulator using a_________.
** Water manometer**
A water manometer provides a cheap and accurate way to measure the low pressures encountered in residential gas systems. Gas valves report pressure settings in inches of water column, which is read with the water manometer.
131
The purpose of the gas regulator vent is to__________.
** allow air to enter above the diaphragm, allow air to escape above the diaphragm, and allow gas to escape if the diaphragm ruptures.**
132
An advantage of the inverted bucket trap is that_________.
** it also vent air and carbon dioxide continuously at steam pressure**
During operation, steam, air and CO2 rise to the 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.
133
Flash theme is caused by_________.
** pipe friction, reduced pressure, And a vertical rise in a condensate line**
134
The purpose of a drip leg in a steam line is to_________.
** let condensate escape by gravity from the fast-moving steam, and store condensate until it can be discharged through the steam trap.**
135
In adequate trapping of steam means often leads to_________.
** 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.
136
Pressure in a vertical condensate pipe will drop 1 psi for every _______ feet in elevation. This is an important factor since boiling temperature drops as pressure drops. When elevating condensate this drop in pressure can cause flash steam.
**2.31**
2.31 feet of head is equal to 1 psi. This is the same factor used in pumping calculations.
137
When using a listening device to test a steam trap, what will the technician listen for that could indicate a problem?
** 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.
138
If an inverted bucket steam trap is blowing live steam. What might the trouble be?
** the valve may have failed to seat because of wear or a piece of dirt or scale, the trap may have lost its prime, or the bucket is stuck or has a hole in it**
139
The__________ drains the condensate from the steam header and returns it to the boiler below the water line while preventing the boiler water from flowing out of the boiler into the return main.
** 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.
140
The__________ is designed to protect boilers against the loss of water do to leaks in the wet return line.
** 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.
141
The control valve in a
sub-atmospheric steam heating system is limited to approximately ______% change per minute.
**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.
142
A vacuum breaker is installed between equipment and a steam trap to_________.
** 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.
143
The most commonly used inspection used on fans and air handling equipment is___________.
** visual**
There is nothing like a good old walk around. An experienced technician can spot trouble without needing expensive equipment, although specialized equipment can confirm that a problem exists.
144
Which air distribution system includes both warm air duct and cool air duct and utilizes mixing boxes near the zone to mix the cool air and warm airstreams to achieve the desired temperature while delivering the air at a near constant volume?
** dual duct**
145
Which duct system delivers constant temperature air at variable volumes?
**VAV**
146
When soldering, solder is drawn into the joint by_________.
** 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 experiments and allows trees to get water from the roots to the crown.
147
Which of the following best describes the difference between brazing and welding?
A. Welding is an adhesive process while brazing is cohesive.
B. Welding is a cohesive process while brazing is adhesive.
C. Brazing is done on non-ferrous metals. Welding is done on ferrous metals.
D. Both B and C.
** B. Welding is a cohesive process while brazing is adhesive.**
148
The practice of installing flanges on pipe and fittings, so that the top bolt hole in the right hand and left hand section of the flange are level with each other is known as_________.
**Two-holing**
This practice makes leveling of fittings and piping easy. The bolt holes in the flanges on flange fittings and valves are drilled according to this rule.
149
Of the valves listed below, which provides the best throttling action
A. Ball valve
B. Globe valve
C. Gate valve
D. Plug valve
** Globe valve**
The flow through a globe valve changes course through two 90° turns causing increased resistance to flow and sometimes a considerable pressure drop.
150
A rating of 125 lb S – 200 lb W.O.G. stamped on a valve means that the valve__________.
** Has a steam rating of 125 psi and a cold water/oil/gas rating of 200 psi**
This rating means the valve can be used with steam up to 125 psi, provided that the temperature does not exceed the value established by the manufacturer. It can also be used with cold water, oil or gas up to 200 psi at ambient temperatures.
151
A device designed to protect pipe insulation against damage because of pipe movement is called a__________.
** pipe saddle**
152
The safe, working load of a fiber or wire rope can be calculated using the formula:
Safe Working Load(SWF)
=
Breaking Strength(BS)
÷
Safety Factor(SF)
where the safety factor for hoisting material is required by OSHA to be______.
**5**
This means that a rope with a breaking strength of 10,000 pounds can safely lift 2000 pounds.
153
Calculate the amount of weight that could be lifted if a force of 100 pounds is exerted in the direction of the arrow.
**300 pounds**
There are three ropes supporting the load in the drawing. Multiplying the force exerted by the number of supporting ropes results in the amount of weight that can be lifted.
154
The weakest portion of a chain hoist is the_________.
** lower hook**
The lower hook is designed to spread when overloaded. The inner contour of the load hook is an arc of a circle and any deviation from this circle is evidence of overloading.
155
An overload of most cable hoist (come-alongs) is prevented__________.
** by a handle that bends**
The manufacturer designs the lever handle to bend before an unsafe load can be lifted. This handle should not be replaced with a stronger bar, nor should cheater devices be used, as both practices will bypass the safety feature.
156
When using a jack to lift a load__________.
** chocks should be used, use wooden softeners, and do not place the jack directly on the ground.**
157
Unless equipped with OSHA or Canadian standards association (CSA) approved ground fault circuit interrupters, portable electric lighting used in wet and/or other conductive locations as for example, drums, tanks and vessels, shall be operated at_____volts or less.
**12**
158
A ladder must extend above the edge of a roof by at least___________.
**Three feet**
159
The proper angle for a ladder is achieved when the distance of the ladder from the building at the base is about_______ the working length (height) of the ladder.
**One fourth**
160
A lock and tag may only be removed by the employee that applied it unless the employee is absent from the workplace, then the lock or tag may be removed by a qualified person designated by the employer to perform this task provided that the employer ensures that__________.
** The employee who applied the lock or tag is not available at the workplace and the employee who applied the lock or tag is aware that it has been removed before he, or she resumes work at that workplace**
161
Section 608 of the Clean Air Act prohibits you from knowingly venting ozone depleting compounds used as refrigerants into the atmosphere while maintaining, servicing, repairing, or disposing of air conditioning or refrigeration equipment (appliances). The date when this prohibition took affect is __________.
**July 1st, 1992**
162
When working on a HCFC-22 appliance or isolated component of such appliance, normally containing 200 pounds or more of refrigerant and using recovery or recycling equipment manufactured or imported on or after November 15, 1993, you are required to evacuate to a level of_________.
**10 in. Hg**
163
If a compressor burnout has occurred, the refrigerant must be__________.
** Recovered and reclaimed**
164
Plot a system curve on the fan curve chart below. Use an operating point of 8000 CFM at a static pressure of 4 in. water column as a basis for your calculations. What will the static pressure be at 7000 CFM?
** 3 in. water column**
Using the formula in the first figure below yields a static pressure of 3.06 in. water column. Plotting the system curve on the figure above shows an operating point at the intersection of the fan and system curves.
165
Calculate the volume in gallons of a cylindrical tank, having a base diameter of 46” and a height of 70”. use the formula in the picture below.
**504 gallons**
23² x 70 x 3.14 = 116,333.175 gallons
116,333.175 ÷ 231*cu.in.* = 503.6
rounded up = **504 gallons**
166
Calculate the velocity of air measured in feet per minute (FPM) in a 36” x 32” duct with 48,000 CFM of airflow. Use the formula below but remember that all units must be in feet.
**6000 FPM**
Area = 36” x 32” ÷ 144 (converting
sq. In. to sq. ft.)
36 x 32 ÷ 144 = 8
48,000 ÷ 8 = **6000 FPM**
167
The symbol in the figure below would be used to indicate a ________ switch that ________ on a rising signal.
**Pressure, Closes**
168
The symbol in the figure below represents a__________.
**Thermopile**
169
The circuit in the figure below represents a___________.
**Current Relay**
