Hello all,


I am searching for a constant pressure expansion valve that is rated for some very tiny capacities, specifically in the range of 250 BTU/Hr to 850 BTU/Hr.

The reason that the capacity is variable is because the compressor RPM is variable, the compressor in question is here; http://www.aspencompressor.com/products/

I will be using the aspen Q4 series, data sheets are available on their site under downloads.

I am shooting for a evaporator pressure of 35 psi using R134a, The system will have a liquid receiver. The evaporator will be refrigerant to water heat exchange with the return water being in the range of 75 to 90 deg F. The maximum ambient operating temperature will be 130 deg F.
The condenser outlet will be 1/4"OD and evap inlet will be 3/8"OD, External equalization will not be necessary.

I was looking at a valve made by parker model a7-aa rated for 1/8th to 1/2 ton, but I fear that that valve will hunt badly on the low end of the compressor RPM. I have already contacted Parker about this and they say that it will most likely hunt and that they do not manufacture a valve of such small sizes.

So what I am asking of you all is if anyone may know of a valve that may fit my needs, I would prefer a valve with ODF connections but I am willing to use other types of connections.

If no such valve exists, then what is your opinion on using a manual needle valve as the expansion device and setting the valve then forgetting it. I would like to avoid using capillary tube due to the cost but a standard orifice would be OK if I had to.

I appreciate any input I am almost to the end of my rope on this plunder.