Question about vave plate of compressors

[A.Mortezania]

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 ?

15274

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.

[monkey spanners]

My understanding is that any gas left in the cylinder and valve plate ports at the top of the compression stroke will have to expand to below the suction pressure before any more refrigerant can be drawn in from the suction side of the system. Smaller ports are beneficial when running high compression ratios as less of the intake stroke is wasted with re expansion volume.

[RANGER1]

Agree with monkey spanners.
Also reduced cost.
Because lower volume of gas being pumped, due to less dense, smaller valves used.

[A.Mortezania]

Thanks monkey spanners and Ranger1 for participating.