RACT Unit 24: Review questions/Practice Test Flashcards
Which is not a pressure or force acting on a TXV diaphragm?
a) spring pressure
b) bulb pressure
c) head pressure
d) evaporator pressure
c) head pressure
The needle and seat of a TXV are normally made of
a) brass
b) aluminum
c) copper
d) stainless steel
d) stainless steel
The TXV tries to maintain a constant ___________ in the evaporator
a) frost line
b) pressure
c) sub cooling
d) superheat
d) superheat
Liquid, Vapour, cross liquid, cross vapour are all types of ________
a) pistons
b) cap tube bores
c) AXV bulb charges
d) TXV bulb charges
d) TXV bulb charges
The bulb of the TXV is mounted on the
a) evap outlet
b) evap inlet
c) comp outlet
d) comp inlet
a) evaporator outlet
When should an externally equalized TXV be used?
a) when there is excessive pressure drop through the evaporator
b) when the system is a low or medium temp application
c) when the system is equipped with a semi hermetic compressor
d) when the txv is used in a low ambient condition on a single circuit evaporator
A) when there is excessive pressure drop through the evaporator
An AXV tried to maintain a constant _________ in the evaporator
a) superheat
b) sub-cooling
c) frost line
d) pressure
d) pressure
The TXV responds to an increased heat load by;
a) increasing refrigerant flow
b) decreasing refrigerant flow
c) not reacting to changing heat loads
d) keeping refrigerant flow constant
a) increasing refrigerant flow
The three factors that determine the capacity of a TXV are: evaporator temperature, liquid temperature entering the valve, and _________
a) pressure drop across the valve
b) number of evaporator circuits
c) length of the sensing bulb transmission line
d) evaporator pressure
a) pressure drop across the valve
How does the automatic expansion valve respond to load increase?
a) it closes, decreasing refrigerant flow
b) it opens, decreasing refrigerant flow
c) it opens, increasing the refrigerant flow
d) it closes, increasing the refrigerant flow
a) it closes, decreasing refrigerant flow
On a ___________ TXV, the liquid pressure is cancelled out because it acts on equal areas but in opposite directions.
a) cross vapour
b) cross liquid
c) balanced port
d) pressure-limiting
balanced port
If a system with a cap tube metering device is properly changed, when it nears the desired box temp it will have a superheat of approximately;
a) 10 to 15F
b) 15 to 20F
c) 8 to 12F
d) 2 to 5F
c) 8 to 12F
A capillary tube meeting device controls refrigerant flow by;
a) pressure drop
b) temperature drop
c) using superheat
d) using a stepper motor
a) pressure drop
On a PID controller, the difference between the superheat set point of the controller and the actual superheat is called ___________
a) derivative
b) integral
c) proportion
d) offset
d) offset
An EEV uses a _____________ to control the valves port, which in turn controls evaporator superheat
a) sensing bulb transmission line
b) stepper motor
c) capillary tube
d) spring
b) stepper motor
The __________ is located inside the valve body and moves the needle in and out of the seat in response to system load changes
a) diaphragm
b) sensing bulb
c) external equalizer
d) transmission line
a) diaphragm
The ___________ charge bulb is usually limited to applications that have narrow operating ranges or to special functions like de-superheating on the high side of the system
a) cross vapour
b) vapour
c) cross liquid
d) liquid
d) liquid
The ___________ on a TXV is used to compensate for pressure drops from the inlet to the outlet of the evaporator
a) internal equalizer
b) needle and seat
c) sensing bulb and transmission line
d) external equalizer
d) external equalizer
To prevent an overloaded compressor during a hot pull down on a low temp cooler, a __________expansion valve can be used
a) balanced port
b) cross liquid
c) pressure-limiting
d) cross vapour
c) pressure limiting
The two factors that determine how much liquid will pass through a cap tube at any given pressure drop are the _____________
a) type of refrigerant and oil
b) spring and bulb pressure
c) length and diameter
d) evaporator and suction line size
c) length and diameter
explain why entering liquid pressure has no effect on the opening force of a balanced-port TXV?
It is cancelled out because it acts in equal areas but in opposite directions
What is meant by MOP TXV
Limit the maximum operating pressure the valve allows the evaporator to experience
Explain why systems equipped with a TXV OR AXV require a receiver?
To store refrigerant when it is not needed
The three pressures that act to open or close a thermostatic expansion valve are _________________ pressure
a) compressor, condenser, evaporator
b) spring, bulb, orifice
c) evaporator, bulb, spring
d) bulb, compressor, evaporator
c) evaporator, bulb, and spring
A TXV with a liquid charged bulb is usually limited to ______________
a) higher temp applications
b) applications that have a narrow operating range
c) systems that operate below atmospheric press
d) applications where the ambient air temp stays above freezing
b) applications that have a narrow operating range
The spring tension on a TXV is factory set for a predetermined superheat of _______F
a) 6-10
b) 8-12
c) 6-8
d) 12-15
b) 8 to 12F
A TXV with a ________ charge bulb, sometimes referred to as a critical charge bulb, is often called a MOP valve
a) vapour
b) cross vapour
c) liquid cross
d) liquid
a) vapour
An external-equalized TXVA must always be installed when a refrigerant distributor is used because of the distributors large pressure drop
true
The external equalizer line should always be piped to the suction line before the expansion valve sensing bulb?
false
Conditions such as large varying head pressures, widely varying evaporator loads, and very low liquid-line temperatures can be controlled by a ________TXV
a) internally equalized
b) MOP
C) pressure-limiting
D) balanced-port
d) balanced port
The controls of a ___________ use algorithms, a set of electronic instructions, and a proportional integral derivative (PID) controller
a) AXV
b) crankcase heater
c) thermostatic expansion valve
d) electronic expansion valve
d) electronic expansion valve
An automatic expansion valve (AXV) is designed to maintain a constant __________ in the evaporator
a) pressure
b) oil level
c) superheat
a) pressure
The ________ does not control superheat, is a fixed bore device with no moving parts and cannot adjust load changes
a) thermostatic expansion valve
b) automatic expansion valve
c) cap tube
d) electronic expansion valve
c) capillary tube