Unit 24 Expansion valves

What is the recommended superheating temp for medium temp evaporators?

(0 - 30°F) 5 - 10°

What is the recommended superheating temp for high temp evaporators?

(30°F) 10 - 12°

What is the recommended superheating temp for low temp evaporators?

(below 0°F) 2 - 5°

At what pressure drop across an air conditioning evaporator would you need and external equalizer?

3 psig

Liquid refrigerant should be completely boiled to a vapor

Approximately halfway through the evaporator

The external equalizer on a TXV is used to _________ for, not getting rid of,________ drops from the inlet to the outlet of the ______

Compensate, pressure, evaporator

The thin metal disc connected to the needle in the TXV is called the

Diaphragm

What type of TXV uses a large port for pull-down capacities and a smaller port for holding loads?

Dual port

What type of valve uses a control board, transistors, thermistors, and a stepper motor controlled by an algorithm?

Electronic expansion valve

A small amount of superheat in the suction line is desirable with a TXV to

Ensure that no liquid refrigerant enters the compressor

Balanced port TXV's are used to

Feed refrigerant at a normal rate with low ambient temperatures

An external equalizer is used when

The pressure drop across the evaporator is excessive

Superheat is

The sensible heat absorbed by the refrigerant after it has boiled to a vapor

What is not a pressure, or force acting on a TXV diaphragm?

Head pressure

When the load on the evaporator increases, the TXV

Increases the flow of refrigerant

What are the four types of charges that the TXV uses to control refrigeration?

Liquid charge, vapor charge, cross liquid charge, cross vapor charge.

What force is cancelled out using a balanced-port TXV?

Liquid force

What are three factors that determine the capacity of a TXV?

Liquid temp entering TXV, pressure drop across TXV, and evaporating temp.

The automatic expansion valve was designed to

Meter refrigerant to the evaporator with an electronic sensing device

The capillary tube is a type of

Metering device

The TXV sensing bulb is mounted

On the suction line between the evaporator and compressor

The pressure-limiting TXV

Shuts off the refrigerant flow to the evaporator when it has reached a predetermined pressure

The needle and seat of a TXV are normally made of____________

Stainless steel

The thermostatic expansion valve regulates refrigerant flow to the evaporator based on

Suction line superheat

The TXV tries to maintain a constant _________ in the evaporator.

Superheat

The sensing bulb and transmission tube are a part of the

TXV