help-Working Principle of Electronic Expansion Valve

[pakblogger2012]

Hi every body ,hope you all will be in sound health and enjoying all in your own way.
I want to know one point regarding working of electronic expansion valve .
A thermistor conveys superheat condition through a circuit to heater with negative temperature resistance coefficient. My question is that how does heater operate needle valve to allow more or less refrigerant to evaporator?
Thanks in advance

[install monkey]

http://www.achrnews.com/articles/electronic-expansion-valves-the-basics
:)

[pakblogger2012]

Thank you sir for your kind reply but my point is still not clear.
The type of expansion valve in link you posted above is different to which I asked.
Please see the following link and read the electronic expansion valve section from where my question originated.
http://www.google.com.pk/url?sa=t&rct=j&q=r%26ac%20lecture%2024&source=web&cd=1&ved=0CDEQFjAA&url=http%3A%2F%2Fnptel.iitm.ac.in%2Fcourses%2FWebcourse-contents%2FIIT%2520Kharagpur%2FRef%2520and%2520Air%2520Cond%2Fpdf%2FR%26AC%2520Lecture%252024.pdf&ei=p4nUUcmcENSt4QTm0oDgDA&usg=AFQjCNHL_tlpzqQTsfHB8goE6jJ4d90QAA&bvm=bv.48705608,d.bGE&cad=rja

[Brian_UK]

The heater probably heats a fluid which will then expand and move the valve needle.

Never seen one myself as now-a-days we tends to use electric stepper motors to drive the valve up and down.

[nike123]

My question is that how does heater operate needle valve to allow more or less refrigerant to evaporator?
Thanks in advance

This is done by electrochemical actuator. It is consisted of heater around thermal actuator. Current of heater is regulated through thermistor which senses evaporator exit temperature.

Thermal actuator:
10526

[pakblogger2012]

Thank you nike123,but one thing is still not clear .
In figure you posted above ,it seems that at higher current actuator will give narrow path for refrigerant flow but actually opposite happens ,above figure does not match actual working of electonic valve.
your guidance please

[nike123]

This is principle of function of piston in valve. Opposite action can be done by spring in assembly. Momentary, I don't have any picture of actual valve.

[moideen]

Thank you nike123,but one thing is still not clear .
In figure you posted above ,it seems that at higher current actuator will give narrow path for refrigerant flow but actually opposite happens ,above figure does not match actual working of electonic valve.
your guidance please

Dear pak,
As per your catalogue, high current will open the valve widely(not narrow path). Anyway thanks you and nike, giving the information about these type EEEV.my experience was only related with stepper motor.