help-How does AXV maintain constant pressure in evaporator ?

[pakblogger2012]

With reference to Automatic Expansion valve ,I would like to have your guidance particularly in following load situations.

How does AXV (Automatic Expansion valve)maintain constant pressure in evaporator when load increases or decreases ?

Thanks in anticipation of your knowledge sharing.

[The Viking]

Short answer: It doesn't.

Slightly longer answer: The AXV, more commonly known as TEV or EEV (Thermal Expansion Valve or Electronic Expansion Vale respectively) regulates the super-heat.
This it does by comparing the temperature of the refrigerant leaving the evaporator with the suction pressure.

The pressure in the evaporator (normally referred to as suction or low pressure) is not constant, on a fully designed and commissioned system it will mainly vary depending on the temperature of the cooled media. The superheat on the other hand should, in an ideal world, be constant.

:cool:

[pakblogger2012]

Thanks for reply.
I think I have freedom to disagree with you The Viking.
An AXV which is also known as constant pressure expansion valve maintains evaporator pressure when load changes are in limited range.
Yes TEV or EEV takes care of superheat also.

Let we have some other views in this thread .

[The Viking]

OK,
Evaporator pressure regulators are normally fitted in the suction line after the evaporator it serves. They can either "back pressure up" in the evaporator or inject hot gas from the discharge after the expansion device to raise the pressure.
Have a look at Danfoss' website (http://www.danfoss.com/Products/Categories/Group/RA/Pressure-and-Temperature-Regulators/Pressure-Regulators/9c8158d8-a37c-4dc1-a102-ef553ad59eb0.html). THIS (http://www.ra.danfoss.com/TechnicalInfo/Literature/Manuals/01/PIHK0B100.pdf) and THIS (http://www.ra.danfoss.com/TechnicalInfo/Literature/Manuals/01/DKRCC.PD.HA0.A2.22.pdf) are two common types.

Sadly what you are describing, one valve that offers both expansion and evaporator pressure control, I never used.

:cool:

[Peter_1]

I have to agree with Parkblogger, an AXV is not more than an expansion device that can be regulated afterwards within some margins.
See it as a cap tube with a variable length and it's placed at the inlet of the evaporator to inject the refrigerant.
It replaces an EEV or TEV http://img.bhs4.com/67/D/67DC0D3B265D85269D8F7AE857BD7337A6C01326_large.jpg
We use it in Maja flakeicemachines and on cascade systems to adjust the DP precisely over the AXV
To answer your question, it doesn't adapt top the load, it maintains only a constant evaporating pressure. So if load decreases, you can have liquid slugging.

[chemi-cool]

Pressure in AXV will change with head pressure. you will have to mantain condensing pressure with fan speed regulation and than you will have constant evaporating temp.