7 replies to this topic

[J_Leo]

Dear Friends,

 

I am evaluating the over-pressure cases on a refrigerant compressor circuit. The compressor curve is attached. From the curve, I think the max discharge pressure would be 120 psia at the surge point.

Am I right?

 

Regards,

Leo

[breizh]

Hi ,

No curve attached !

Breizh

[J_Leo]

Sorry, the curve is attached now.For the first time, I selected the file and forgot to click attach button.

 

Leo

Attached Files

•  centrifugal compressor curve.pdf   37.65KB   70 downloads

[Pilesar]

The curve you attached shows max discharge pressure would be 120 psia at the surge point. Just because a curve shows something does not mean it represents reality. Your curve does not even look like a manufacturer's head curve. I would not trust it as evidence of anything.

[Bobby Strain]

Maybe this is a screw compressor? A single curve is not sufficient to predict maximum discharge pressure. One must evaluate the whole refrigeration system.

 

Bobby

[J_Leo]

Hello Pilesar and Bobby,

 

This is the curve for an existing centrifugal compressor from the vendor. There are a couple of head curves in the operation manual. My initial though was to select the biggest surge pressure among a couple of curves in the manual.

Bobby, can you give me some advice on how to evaluate the refrigerant system to determine the max discharge pressure?

 

Thank you so much,

-Leo 

[Bobby Strain]

It's like which came first, the chicken or the egg. Usually one sets the compressor discharge to protect downstream equipment. If this is a new design you need to choose what is to set the discharge pressure. It's usually related to the condenser cooling media condition.

 

If you want to evaluate an existing situation, the maximum discharge pressure is a function of the discharge relief valve capacity. If the flow from the discharge system is restricted, then the pressure will increase until the relief valve will pass whatever flow is generated in the evaporators. So, there is not one simple answer.

 

Bobby

Edited by Bobby Strain, 18 January 2018 - 05:21 PM.

[J_Leo]

Bobby,

 

Thank you so much. I will look into it and see what happens.

 

-Leo