Dear Friends,
I have a question.
As you know valve plate of compressors that work in low temperatures have smaller diameter of discharge valve port (photo at below).
Also at "compression ratio = Discharge pressure / Suction pressure" compression ratio depends on suction and discharge pressure.
I do not think smaller diameter of discharge port helps on more compression. By this do anyone can help me and say me what is advantage of smaller diameter on port of discharge on low temperature compressors that helps us to go to lower temperatures on evaporator ?

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You can see high temp. valve plate has 3 wide port of discharge and low temp. valve plate has 2 thinner port of discharge.

Copland says this help on increasing "Volumetric efficiency" of compressor but I think beside of this, This thinner port of discharge also must help on other subject that helps us to go to lower temperature in evaporator.

Sincerely yours.