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ebaid
28-02-2016, 05:06 PM
I have a 2 stage Grasso package P & W frames, when the compressor stops suddenly the check valve doesn't close right and it rotates in the reversed direction with a noisy voice. when the service engineer arrived he changed the discharge pressure from 10.5 bar to 13 bar to avoid this action.
this change decreased the refrigeration capacity and made the oil temperature higher than 55 C
what should I do to solve these problems?

Grizzly
28-02-2016, 05:36 PM
Welcome ebaid.
I fail to understand how increasing the discharge pressure and therefore the pressure / gas volume differential.
Would make the compressor Scream any less! (As the higher discharge gas pressure balances out it will drive the screw backwards!)
Or has the higher discharge setting meant that the compressor no longer reaches set point.
So it does not stop?
Whatever! The real answer is get the Non Return Valve fixed.
The extra energy consumed by the compressor alone will more than pay for the repair!

You do say when the comp stops suddenly?
Could you explain?

Thanks Grizzly

PaulZ
29-02-2016, 02:40 AM
Hi ebaid
Agree with Grizzly, putting the discharge pressure up will make it worse. Put the discharge back to 10.5 bar and fix the non return valve.
Paul

ebaid
29-02-2016, 04:15 PM
the check valve has internal piston to close using the discharge gas pressure from oil separator, when we dismantled the check valve we found that it works well by using compressed air to actuate the valve.
so, the best choice is to decrease the pressure and neglect reversed rotation or to keep the pressure high??

I have also another problem in the other package:
during starting up;when the HP compressor starts it makes the LP compressor rotate with high speed for long time (without starting LP drive motor) so that there is no oil lubrication in LP compressor during that period

what do you think about this fault?

RANGER1
01-03-2016, 12:38 AM
Ebaid,
Can I ask which check valve you are referring too.
Mic machine runs backwards on shut down its suction check & replace as previously stated for reliability.
As for other package not sure how GEA set up duo, but see that first stage compressor has to rotate if only high side running.
I would have thought first stage should run promptly after second stage high side compressor starts.
Is there another line from low side suction going to high side suction with check valve in it as well?