Expansion Devices Flashcards
7 cards from real RSES practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Expansion Devices flashcards as text
What happens to refrigerant pressure as it passes through a thermostatic expansion valve (TXV)?
Answer: Pressure drops from high-side to low-side pressure
The TXV creates a pressure drop that allows the refrigerant to flash from liquid to a low-pressure mixture entering the evaporator.
A TXV with an external equalizer senses evaporator pressure at which location?
Answer: At the evaporator outlet
The external equalizer line connects to the evaporator outlet, allowing the valve to sense actual evaporator pressure rather than inlet pressure.
Which condition would cause a TXV to be in the fully closed position?
Answer: Low superheat at the bulb location
Low superheat indicates excessive liquid refrigerant at the evaporator outlet, causing the TXV bulb pressure to drop and close the valve.
What is the typical superheat setting range for a TXV used in air conditioning applications?
Answer: 8-12°F
Most air conditioning TXVs are factory set for 8-12°F superheat to ensure full evaporator use while protecting the compressor.
An automatic expansion valve (AEV) maintains constant:
Answer: Evaporator pressure
The AEV modulates to maintain a constant evaporator (low-side) pressure regardless of load changes.
Which type of expansion device is most commonly used in small hermetic refrigeration systems like household refrigerators?
Answer: Capillary tube
Capillary tubes are inexpensive, have no moving parts, and are well-suited to fixed-load applications like household refrigerators.
What effect does increasing the length of a capillary tube have on system performance?
Answer: Decreases refrigerant flow rate
A longer capillary tube increases friction resistance, reducing refrigerant flow rate and lowering evaporator pressure.