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56 terms

NATE: TEV, TXV

STUDY
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The term hunting refers to which type of metering device:
thermostatic expansion valve
MOP refers to which type of metering device:
thermostatic expansion valve
In a valve having a MOP (maximum operating pressure), if the pressure in the evaporator increased higher than the MOP of the valve, the valve would then tend to:
close until pressure is reduced
Liquid charge, liquid cross-charge, gas charge, or gas cross-charge refer to:
sensing bulb charges of a TXV
A liquid charge-sensing bulb contains:
the same refrigerant as in the system
A liquid cross-charge-sensing bulb contains:
a mixture of refrigerants that are different from that of the system
The type of sensing bulb that will prevent liquid floodback on system's startup is the:
gas and gas cross-charge
The sensing-bulb type that has its own MOP is the:
gas charge and gas cross-charge
To increase the superheat on a TXV one would:
turn the adjusting stem clockwise
To decrease the superheat on a TXV one would:
turn the adjusting stem counterclockwise
The superheat can be defined as a ____ that is ____its saturation temperature for a given pressure.
gas; above
When a TXV tends to overfeed or underfeed in an attempt to find a balance point and become stable, it is known to be:
hunting
The main function of the thermostatic expansion valve is to ____ refrigerant flow and ____ a constant superheat.
regulate: maintain
When superheat increases at the evaporator outlet, the TXV will:
open more
The thermostatic expansion valve will decrease refrigerant flow when the superheat at the evaporator outlet:
lowers
When a thermostatic expansion valve is used, the system's refrigerant charge is generally not as critical as it would be with:
a capillary tube
The sensing bulb is part of the TXV and is connected to the valve by a capillary tube to the:
top of the valve's diaphragm
Pin, pin carrier, and pushrods are all components of the:
TXV
The component of a TXV that actually adjusts superheat is called the:
superheat spring
Which is not an operating pressure of a thermostatic expansion valve:
condenser pressure
Which of the following pressures tends to close the TXV valve:
evaporator pressure/spring pressure
The pressure that tends to open the TXV valve is the:
bulb pressure
When the system is in normal operation the sensing-bulb pressure should equal the:
spring and evaporator pressure
The function of the sensing bulb is to:
sense the temperature of the refrigerant vapor as it leaves the evaporator coil
Which pressure of the TXV will allow the valve pin to lift off the valve port:
bulb pressure
When will the TXV valve pin move to close off the valve port:
when bulb temperature and pressure are reduced
When there is an increase in heat load on the evaporator, the refrigerant will tend to:
evaporate at a faster rate
The term ____ refers to a method of bleeding off or allowing evaporator pressure to pass through a passageway within the valve body.
internally equalized
The external equalizer line is connected to:
a suction line
Thermostatic expansion valves that are internally equalized should be used with:
single-circuit evaporators with no more than the equivalent of 2° F saturated temperature change
The equalizer line should never be:
capped off
The external equalizer uses:
evaporator pressure at the evaporator outlet
The term thermostatic charges refers to:
the substance in the sensing bulb that responds to suction line temperature
Which is not classified as a thermostatic charge:
lubricated charge
The liquid charge-sensing and gas charge-sensing bulb is commonly charged with:
the same type of refrigerant that is in the system
The ____ charge TXV will always have some liquid within the bulb, capillary, and diaphragm.
liquid cross-
Which thermostatic charge element contains a mixture of refrigerant that will condense to a small quantity of liquid when the TXV is in its normal operating range:
gas cross-charge
Which thermostatic charge element has a noncondensable gas along with a special material within the sensing bulb:
adsorption charge
The term "MOP" refers to:
maximum operating pressure
Whenever a refrigerant distributor is used on an evaporator coil, a:
TXV with an external equalizer should be used
The external equalizer line should be connected:
downstream from the sensing bulb
A de-superheating TXV is used in conjunction with:
a hot gas or discharge bypass valve
The de-superheating TXV allows refrigerant to:
cool the hot discharge gas that enters the suction line
Specially designed thermostatic expansion valves must be used when the system's refrigerant is:
R-717
Refrigeration systems will generally operate with ____ than air conditioning systems.
a lower superheat
Thermostatic expansion valves can be installed:
in any position but as close to the evaporator as possible
When a refrigerant distributor cannot be directly connected to the TXV outlet, the maximum distance between the valve outlet and the distributor should not exceed:
24"
The only component that should be installed between the TXV outlet and the evaporator is the:
refrigerant distributor
Static pressure will always be present in the liquid line when the TXV and the evaporator are located:
above the receiver
The contact of the TXV sensing bulb on the suction line should be direct on the piping and connected with:
two bulb straps
The TXV sensing bulb needs to be placed at the 4 o' clock or the 8 o' clock position on the suction line when the line is:
7/8" OD or larger
The TXV sensing bulb should be installed on top of the suction line when the line is:
smaller than 7/8" OD
When an application calls for brine tanks and water coolers to be used, the sensing bulb should be:
below the liquid surface
Which statement is true of a thermostatic expansion valve:
Some valves are of the nonadjustable type
What is the most accurate means of determining TXV performance:
superheat measurements
In general, the correct superheat will be determined on the amount of temperature difference between the:
refrigerant temperature and the temperature of the suction line