how a thermal expansion-valve operates?

Answer 1

*A thermostatic expansion valve ( TXV) is precision device used to meter the flow of liquid refrigerant entering the evaporator at a rate that matches the amount of refrigerant being boiled off in the evaporator, This is it's main purpose but like all the other metering devices it also provides a pressure drop in the system, separating the high pressure side of the system from the low pressure side. thus allowing low pressure refrigerant to absorb heat onto it's self.
*Externally equalized TXV's must be used when the pressure drop in the evaporator exceeds :

3 Deg. F for Air Conditioning

2Deg.F for Refrigeration

1Deg.F for Low Temp applications
* The valve it self has 3 forces that act upon each other to accomplish this task. They are:
Bulb Pressure P1
Evaporator Pressure P2
Spring Pressure P3
*In equilibrium: P1 = P2+P3. If the evaporator pressure was to increase while the bulb pressure stayed that same the valve would close. P2 + P3 would be greater than P1. Now if the bulb pressure was to increase to the larger amount, the valve would open . P1 is greater than P2+P3.

Pl. visit:
http://www.hvacmechanic.com/txv.htm

Answer 2

This kind of valve is used very widely in HVAC+R (heating ventilation airconditioning and refrigeration). It consists of a small chamber (sensor bulb) containing a volatile liquid (it has to bee volatile in the temperature range the valve is designed to work in) that is conected on the other side with a diaphargm that can move the valve spindle. On a certain temperature (on the sensor bulb) liquid inside evaporates and increases the pressure which moves the diaphargm and the valve spindle which results in closing the valve (or opening depending on construction). When the temperature drops, the gas turns to liquid again, the pressure inside drops and the valve is open again (or closed). So in this way you can open or close (regulate) a valve depending on the temperature with no energy required.

Answer 3

A TEV is used in refrigeration to regulate the flow of liquid refrigerant into the evaporator coil.

The TEV actuator consists of a bulb containing a volatile liquid connected via a capilary tube to a bellows assembly mounted on the body of the TEV. The Sensing bulb is attached to the outlet side of teh evaporator. If the Evaporator outlet is too cold the liquid in the sensing valve contracts removing pressure from the bellows(or diaphram) which lets the TEV close. This cuts the flow of refrigerant through the evaporator allowing the evaporator to warm up. As it warms up the sensing bulb temp warms and the liquid expands causing the TEV to open.

Answer 4

Guessing purely by the name: It heats up a liquid or gas inside it, which makes the fluid expand, which presses on the valve