gas pulsations

hello everyone,
can anyone explain me these lines in grasso screw compressor manual i need to understand what is meant by gas pulsations in discharge area and why a connection from the oil separator can stop these gas vibrationnsAttachment 13903

Ahmed,
Guessing this information is out of Grasso screw manual?
I think it reduces noise with discharge pressure piped to special port in slide valve.
It would be from their own in house knowledge & testing.
It probably prevents back flow of gas in certain situations, loads & high compression ratios.
Have seen it piped up on single stage economized screw.

thanks you for your reply and yes they say in high compression ratios but why specially in high compression ratios i really wish if i can understand the scientific reason for this piping :)

Attachment 13904

OK it's upside down as usual.
Do not profess to know how it helps but if picture the correct way up, slide valve is fully unloaded, small slotted ports are exposed to oil separator discharge pressure, see left hand side of slide.
If loaded up ports then blanked off to oil sep pressure.
So it appears to only come into effect when fully unloaded.
This must reduce gas pulsation in this area causing possible noise & vibration.
Cricri would be able to add to it if he sees this post

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High compression ratios in low load situations?

High compression ratio would be the result of a low temperature
freezer application and an air cooled condenser or such? With a temp
lift from -30ish to say +40ish, thats a good 70 degree difference and
then combine that with a low load situation, the unloading slide could
be causing gas to pass back from the high side to the low side and that
could cause micro pulsations that build in resonance and cause pulsations
or vibration?

Almost like a gauge flutters on a piston comp.

Rob

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