RSES Expansion Devices 3 — Questions and Answers
Question 1: A float valve in a flooded evaporator system responds to changes in:
- Refrigerant temperature
- Refrigerant liquid level (Correct answer)
- Suction line pressure
- Compressor discharge pressure
Correct answer: Refrigerant liquid level
The float valve maintains a constant liquid refrigerant level in the flooded evaporator by opening and closing based on liquid level.
Question 2: What is the primary advantage of an electronic expansion valve (EEV) over a TXV?
- Lower cost and simpler installation
- More precise refrigerant flow control across varying conditions (Correct answer)
- No need for a refrigerant charge
- Eliminates the need for a compressor
Correct answer: More precise refrigerant flow control across varying conditions
EEVs use electronic controls and stepper motors for precise modulation, outperforming TXVs in variable-load or multi-evaporator applications.
Question 3: The TXV sensing bulb must be mounted in proper thermal contact with the suction line because:
- It measures system amperage
- It must accurately sense refrigerant temperature to control superheat (Correct answer)
- It provides structural support for the valve
- It measures ambient humidity
Correct answer: It must accurately sense refrigerant temperature to control superheat
The sensing bulb contains a refrigerant charge that expands or contracts based on suction line temperature, which opens or closes the TXV.
Question 4: Which of the following would cause a TXV to hunt (cycle open and closed rapidly)?
- Correct superheat setting
- Oversized TXV for the system load (Correct answer)
- Proper bulb insulation
- Correct refrigerant charge
Correct answer: Oversized TXV for the system load
An oversized TXV over-responds to load changes, causing hunting as it continually opens too far then closes too far.
Question 5: In a refrigeration system using a capillary tube, what happens during the off cycle?
- Pressures equalize between high side and low side (Correct answer)
- High-side pressure continues to build
- Low-side pressure drops further
- Refrigerant migrates to the condenser only
Correct answer: Pressures equalize between high side and low side
A capillary tube has no check valve function, so pressures equalize during the off cycle, making startup easier for the compressor.
Question 6: What is the function of the distributor nozzle connected to a TXV outlet in a multi-circuit evaporator?
- It regulates superheat independently
- It evenly distributes refrigerant to all evaporator circuits (Correct answer)
- It prevents liquid floodback
- It measures refrigerant quality
Correct answer: It evenly distributes refrigerant to all evaporator circuits
The distributor nozzle splits the refrigerant mixture from the TXV into equal portions for each evaporator circuit to ensure uniform loading.
Question 7: A TXV that is overfeeding (flooding) the evaporator will most likely cause:
- High superheat at the evaporator outlet
- Liquid refrigerant entering the compressor (Correct answer)
- High condensing pressure
- Reduced refrigerant charge
Correct answer: Liquid refrigerant entering the compressor
Overfeeding sends excessive liquid through the evaporator, and unevaporated liquid entering the compressor causes liquid slugging damage.
RSES Expansion Devices 3
A float valve in a flooded evaporator system responds to changes in: