RSES Expansion Devices 4

Question 1

What three forces act on the TXV needle/pin to control refrigerant flow?

Accepted Answer

Bulb pressure, evaporator pressure, and spring pressure

Answer

The TXV balances bulb pressure (opening force) against evaporator pressure plus spring pressure (closing forces) to modulate flow.

Question 2

When installing a TXV sensing bulb on a suction line larger than 7/8 inch OD, the bulb should be mounted at:

Accepted Answer

The 4 or 8 o'clock position

Answer

On larger suction lines, mounting the bulb at the 4 or 8 o'clock position ensures it contacts refrigerant vapor rather than oil that pools at the bottom.

Question 3

Which expansion device is best suited for a system with widely varying load conditions?

Accepted Answer

Thermostatic expansion valve

Answer

The TXV modulates based on superheat sensing, making it ideal for systems with variable loads unlike fixed-restriction devices.

Question 4

A clogged or restricted TXV will cause the suction pressure to:

Accepted Answer

Drop below normal

Answer

A restricted TXV starves the evaporator of refrigerant, reducing suction pressure and causing abnormally low evaporator temperatures.

Question 5

What is meant by the term 'static superheat' in a TXV?

Accepted Answer

The superheat setting due to spring tension alone when bulb and evaporator pressures are equal

Answer

Static superheat is established by the valve spring's initial tension and represents the minimum superheat before the valve begins to open.

(RSES) Refrigeration Service Engineers Society Certification Practice Test

(RSES) Refrigeration Service Engineers Society Certification Practice Test

RSES Expansion Devices 4