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Evap, Cond, MD, Receivers > Powerpoint: Metering Devices > Flashcards

Powerpoint: Metering Devices Flashcards

1
Q

A metering device is a _____ device

A

control

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2
Q

A Metering device does 2 things:

  1. Meters refrigerant into the _______
  2. Provides a pressure drop to change _______ temp and produce _____ gas
A
  1. evaporator

2. saturation temp, flash gas

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3
Q

A metering device separates the _____ side from the _____ side

A

high side from the low side

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4
Q

A metering device is installed at the ____ of the _________

A

inlet of the evaporator

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5
Q

Operation:

  1. Refrigerant enters the metering device as a ____ pressure, ______ temp ___ _____ liquid
A
  1. high pressure, medium temperature sub-cooled liquid
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6
Q

Operation:

  1. The liquid refrigerant flows through a ________ orifice where the pressure will be decreased, as a result;
  2. Refrigerant will leave the MD as a ____ pressure, ____ temperature saturated liquid vapour mix of ___% vapour and ___% liquid
  3. The ideal saturated temperature for air conditioning is ___F
A
  1. restricting
  2. low, low, 25% vapour 75% liquid
  3. -40F
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7
Q

Types of Metering devices;

  1. _____ expansion (needle valve)
  2. fixed _____
  3. _______ tube
  4. Acc-____
  5. automatic ________ (not easy to work with)
  6. thermostatic _______ (most popular)
  7. electric ______ valve
  8. electronic ______ valve
  9. ____ side float (mostly in chillers)
  10. ____ side float
A
  1. hand expansion (needle valve)
  2. fixed orifice
  3. capillary tube
  4. Accuator
  5. automatic expansion (not easy to work with)
  6. thermostatic expansion (most popular)
  7. electric expansion valve
  8. electronic expansion valve
  9. high side float (mostly in chillers)
  10. low side float
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8
Q

Name 3 pressure operated MD types;

A
  1. hand expansion valve (needle)
  2. fixed orifice
  3. capillary tube
  4. automatic expansion valve
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9
Q

Name 2 volume operated MD types;

A
  1. high side float

2. low side float

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10
Q

Name 3 temperature operated MD types:

A
  1. thermostatic expansion valve
  2. electric expansion valve
  3. electronic expansion valve
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11
Q

Hand expansion valve:

  1. It is a needle valve that is _____ operated
  2. A change in load requires _____ adjustment of the valve
  3. Now commonly used where another device will control flow to the valve automatically( _____)
A
  1. hand
  2. manual
  3. solenoid
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12
Q

Fixed Orifice (cap tube):

  1. A small accurate inside diameter tube that offers high _______ resistance to refrigerant flow
  2. There is no _____ change along the tube as flashing should not occur until ref leaves capillary tube and enters the evaporator
A
  1. frictional

2. temperature

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13
Q

Fixed Orifice: Capacity affected by any change in;

  1. Length: longer means ____ refrigerant
  2. Inside diameter: larger means ____ refrigerant
  3. Pressure difference: increase means _____ ref
A
  1. less refrigerant
  2. more refrigerant
  3. more refrigerant
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14
Q

Capillary Tube Characteristics:

  1. Space temp controlled by __________
  2. Off cycle equalization as there is no actual separation between _______ and ________
  3. Critically charged system- meaning it has just enough refrigerant for the _____ it was designed for
A
  1. thermostat
  2. high side and low side
  3. load
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15
Q

Critical charger systems usually have a fairly _______ load

A

constant

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16
Q

critically charged systems have no _______ of refrigerant for load changes

A

reserve

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17
Q

______ down is a procedure to relocate refrigerant from the low side to the receiver.

A

Pump

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18
Q

Pump down systems have a liquid line _______ valve to prevent migration

A

solenoid valve

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19
Q

Capillary Tube Advantages:

  1. Inexpensive and only requires a low starting torque _________
  2. No ______ parts
  3. _______ design
A
  1. compressor
  2. moving
  3. simple
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20
Q

Capillary tube disadvantages:

  1. does not respond well to _____ changes
  2. The small ______ diameter will plug easily with any ______ in the system
A
  1. load changes

2. inside diameter, debris

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21
Q

Fixed Orifice Actuator:

  1. works basically the same as the _____ tube
  2. It is more compact and can be used as a ______ valve in _____ pump applications
  3. It requires careful selection to match _______ with installed system
  4. It is a ________ charged system
  5. No separation between _____ side and ______ side
A
  1. capillary tube
  2. check valve, heat pump
  3. orifice
  4. critically charged
  5. high side and low side
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22
Q

Automatic Expansion Valve:

One of the first automatic expansion valves is designed to maintain a constant _______ in the evaporator

A

pressure

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23
Q

Automatic Expansion Valve:

Operates under 3 pressures; name all 3

A

Spring pressure (opening force)

Atmospheric pressure (opening force)

Evaporator pressure (closing force)

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24
Q

Automatic Expansion Valve:

  1. When evaporator pressure drops, spring pressure and atmospheric pressure will cause the valve to _____
  2. When evaporator pressure increases the evaporator pressure will overcome the spring and atmosphere pressure cause inflation the valves to ______
A
  1. open

2. close

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25
Q

Automatic Expansion valve characteristics:

  1. Space temp controlled by a _________
  2. not recommended for varying _____ applications
  3. As load increases the valve tends to ______
  4. As load decreases the valve tends to ______
  5. It is a ________ charged system
  6. Suction accumulators should be used due to possible _________
A
  1. thermostat
  2. load
  3. close
  4. open
  5. critically
  6. floodback
26
Q

Low side Float:

Is a liquid level control located on the ____ side of the system it operates on the rate of ________

A

low side, rate of evaporation

27
Q

Low side float:

As the load increases, more _________ evaporates, the liquid level in the evaporator decreases and the valve will open on decrease of liquid level

A

refrigerant

28
Q

Low side Float:

May be used on _____ or ________ systems

A

direct or indirect

29
Q

Low side Float:

  1. If not critically charged may have a ______ to store ref for variations in load
  2. Used on ______ coils
  3. Simple and ______
  4. Low side float are common on ______ systems
  5. low side float may be arranged with a ____, hand expansion valve, high/low level alarms. This arrangement is commonly called ________ float switch
A
  1. receiver
  2. flooded
  3. reliable
  4. ammonia
  5. LLS (liquid line solenoid), electric float switch
30
Q

High side Float:

  1. Liquid drops, they _____. Liquid rises, they _____
  2. A liquid level control, located on the _____ side of the system operates at rate of _________
  3. As the load increases more refrigerant evaporates, more ref condenses as the liquid level in the condenser increases the valve will _____ on increase of liquid level in the condenser
  4. May be used on _____ or _______ systems
A
  1. Close, Open
  2. high side , rate of condensation
  3. open
  4. direct or indirect
31
Q

High side Float:

  1. Medium temp controlled by ______ and _________
  2. It is a _______ charged system
  3. Evaporator may be ______ or ______ expansion
A
  1. pressure and temperature
  2. critically
  3. flooded or dry (DX)
32
Q

Pilot operated HSF valve:

  1. Pilot float valve follows the ______ level
  2. As the condensing load increases the _____ ball rises, slowly closing the pilot orifice
A
  1. liquid level

2. float

33
Q
  • Thermostatic Expansion Valve:
    1. Operation: Refrigerant flow control for ___ evaporators
    2. Controls the flow of refrigerant by maintaining a constant _______
A
  1. DX (dry)

2. constant superheat

34
Q

*TXV main parts (thermostatic expansion valve)

  1. _________ element (top)
  2. Push ____ (mid)
  3. external ________ connection (mid/low)
  4. _____ body (low)
A
  1. thermostatic element
  2. push rods
  3. external equalizer conn.
  4. valve body
35
Q

TXV valve body:

  1. machined ____ or stainless ____
  2. holds __________ together
  3. provides means to connect valve to the _______ circuit
  4. fastened by _____, ______ or flange
  5. has an _____ screen to stop any small particulate matter from entering the _____
A
  1. machined brass or stainless steel
  2. components
  3. to the piping circuit
  4. flare, solder, or flange
  5. inlet screen, the valve
36
Q

TXV Diaphragm:

  1. Moves the needle in and out of the seat in response to ______ ______ changes
  2. Flexes downward to _____ the valve
  3. Flexes upward to _______ the valve
  4. made of thin flexible _______ ______
  5. located at the ___ of the valve
A
  1. system load changes
  2. open
  3. closes
  4. stainless steel
  5. top
37
Q

TXV Valve: Needle and Seat;

  1. Controls ref _____ through the valve
  2. Needle is pushed into the seat to reduce refrigerant flow to the ________
  3. Made of ________ steel
  4. Greater _______ difference across the needle and seat the greater the amount of flow through the valve
A
  1. flow
  2. evaporator
  3. stainless steel
  4. pressure
38
Q

TXV Valve: The Spring;

  1. One of the valves _______ forces
  2. Acts to push the needle into the seat causing the valve to ______
  3. Spring pressure determines the evap ________
  4. spring tension can be _____ adjusted
A
  1. closing
  2. close
  3. superheat
  4. field adjusted
39
Q

The Sensing Bulb and Transmission Line:

  1. Senses temperature at outlet of _______
  2. this temp is converted to a pressure and is transmitted to the top of the ________
  3. fluid in the bulb responds to a ____/____ relationship
  4. when the suction line temp goes up the bulb pressure goes ____
  5. The bulb pressure is the only opening pressure that controls the _____
A
  1. evaporator
  2. diaphragm
  3. press/temp
  4. up
  5. valve
40
Q

TXV Valve:

Name the three pressures and what they do to the valve (open or close)

A

Spring (closes)

Evaporator (closes)

Bulb (opens)

41
Q

TXV Valve:

As the load on the evaporator increases the superheat will increase. TXV senses change in superheat through the ____

A

bulb

42
Q

TXV Valve:

Bulb pressure increases putting more pressure on the diaphragm of the valve overcoming spring pressure and evaporator pressure to force the valve to ______ allowing more liquid/vapour to enter the evaporator

A

open

43
Q

TXV Valve:

As the load on the evaporator decreases the superheat will ________. TXV senses the change in superheat through the bulb

A

decrease

44
Q

TXV Valve:

Bulb pressure decreases putting less pressure on the diaphragm of the valve spring pressure and evaporator pressure overcomes bulb pressure to force the valve to _____

A

close

45
Q

TXV Equalization: Internally equalized;

  1. Used on ______ evaporators
  2. Push rods are _______ shaped
  3. evaporator inlet pressure has direct access to the bottom of the _______
A
  1. single
  2. triangular
  3. diaphragm
46
Q

TXV Equalization: Externally equalized;

  1. used of an evap has more than ____psig drop from inlet to outlet
  2. evap press is sensed at the _____ of the coil instead of the ______
  3. Used on multi circuit evaporators equipped with a _______
A
  1. 2.5psig
  2. outlet instead of the inlet
  3. distributor
47
Q

TXV control one thing;

A

superheat

48
Q

Why are multi-circuit evaporators used on external equalizers?

A

It is more efficient because it reduces a large pressure drop

49
Q

TXV Sensing Bulb:

The _____ charge provides the temp operating characteristics for the valve

A

bulb

50
Q

TXV Sensing bulb:

Types of bulb charges;

  1. _____ charge
  2. ___ liquid charge
  3. _____ charge
  4. _____ vapour charge
A
  1. liquid charge
  2. cross liquid charge
  3. vapour charge
  4. cross vapour charge
51
Q

The Liquid Charge Bulb;

  1. bulb contains the ______ refrigerant as the refrigerant system
  2. contains enough liq ___/____for a wide range of temperatures
  3. The ref in the bulb will always follow the ____/____ relationship of the system
A
  1. same
  2. ref/vap
  3. press/temp
52
Q

The Cross-Liquid Charge Bulb;

  1. Bulb contains ______ ref than system
  2. Contains enough ref/vap for a wide range of ________
  3. the bulb _____ ___ follow the press/temp relationship of the system
A
  1. different
  2. temperature
  3. does not
53
Q

The Vapour Charge Bulb:

  1. Bulb contains ____ ref as system
  2. bulb contains just enough _______ refrigerant for valve operation within its temperature range
  3. Also called a _______ charge bulb
  4. At some predetermined temp, all of the liquid in the bulb will _____ until only ______ remains
  5. Any further increase in bulb temp will have no effect on bulb _______
  6. Also known as ______ limiting or ____ value
A
  1. same
  2. liquid
  3. critical
  4. boil, vapour
  5. pressure
  6. pressure, MOP
54
Q

Pressure Limiting or MOP Value:

  1. Used to limit _____ loading (suction pressure) during hot pulldown or after defrost
  2. This press limiting charge causes the ____ to remain closed until the system evap pressure is reduced below ____ of charge
  3. Due to design of pressure limiting charges, the valve diaphragm and cap tubing must be kept at a temp _______ than the bulb during system operation.
  4. Otherwise, migration of the charge away from the bulb will occur, and cause loss of _____ _______
A
  1. compressor
  2. TXV, MOP
  3. warmer
  4. valve control
55
Q

The Cross Vapour Charge Bulb:

  1. bulb contains ______ ref than system
  2. bulb contains just enough _____ ref for valve operation within its temperature range
  3. bulb does not follow the ____/_____ relationship of the system
  4. operating characteristics are similar to the _____ charged bulb
A
  1. different
  2. liquid
  3. press/temp
  4. gas
56
Q

TXV Sensing Bulb Mounting:

  1. bulb should be mounted on the ______ line as close to _______ as possible
  2. suction line should be ____ and _______
  3. bulb must be mounted _______
  4. bulb must be well ________
  5. for small suction lines the bulb is usually secured to the ____ of the line
A
  1. suction , evaporator
  2. clean and straight
  3. securely
  4. insulated
  5. top
57
Q

TXV Sensing Bulb Mounting:

  1. For lines 7/8” OD and larger, locate bulb between __ and __ o’clock
  2. Bulb must be located atleast ___” from where suction line exits the conditioned space
  3. Where possible, bulb should be mounted ______ of the equalizer connection to the suction line
  4. Access tube in the down position to prevent trapping of ______ charge
  5. Coil excess capillary tube on top of the thermostatic element to ______ it
  6. Do not locate the bulb on the coil _______ header
A
  1. 8 and 4 o’clock
  2. 18”
  3. upstream
  4. liquid
  5. protect
  6. suction
58
Q

What does MOP stand for?

A

Maximum operating pressure

59
Q

Expansion Devices:

  1. Often called _______ devices
  2. Meter the correct amount of refrigerant to the _________
  3. Installed in the ______ line between the ________ and the __________
  4. Three types are; ____ , auto_____ expansion valve, ______ bore
A
  1. metering
  2. evaporator
  3. liquid line between the cond and evap
  4. TXV, automatic expansion valve , fixed bore
60
Q

Thermostatic Expansion Valve (TXV):

  1. Meters the refrigerant to the evaporator by using a _________ _______ element
  2. Maintains a constant evaporator ___________
  3. If the evap superheat is high, the valve will ______
  4. _________ ensures no liquid ref leaves the evap
  5. Low superheat _______ the net refrigeration effect
A
  1. thermal sensing element
  2. superheat
  3. open
  4. superheat ensures
  5. increases

Evap, Cond, MD, Receivers (16 decks)

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