9 replies to this topic

[motaleby]

Dear engineers

What happen if both suction and discharge valves of a reciprocating compressor are closed but the spill back valve still open?

Regards

[samayaraj]

Motaleby,

 

This condition should never happen for a reciprocating compressor. If you close suction and discharge valve, the hold up gas within suction valve & compressor will be discharged through spill back valve and compressor will trip on overload due to formation of vacuum in the suction.

 

 

#Samayaraj

Edited by samayaraj, 02 February 2015 - 03:15 AM.

[motaleby]

Dear Samayaraj

 

Yes I know, we are working on Hazop Study of this equipment now and want to know the consequences of this faults. Some of us bielive that we will have "piping rupture or valve" , some say "compressor trip" will be occured and the rest predicted the compression will be countiued untill Ps=Pd !

What do you think now?

 

thanks a lot

motaleby

Edited by motaleby, 02 February 2015 - 04:32 AM.

[fallah]

motaleby,

 

Those are attending in such HAZOP meeting with having the relevant P&ID and related documents in hand have three different ideas about the consequences of mentioned valves closure. Now, how can we submit a proper response without having at least a simple sketch of the compressor system?

 

Please provide adequate info and sketch of the system...

[manish.bharadwaj]

A small question..Why both valves are considered as close in Hazop? 

 

We shall not consider malfunction of both Suction & Discharge valves at same time as this is creating double jeopardy. 

 

As asked by Mr Fallah provide additional info.

[rychurek]

If we assume that:
1.compressed gas is cooled
2.Suction,discharge valve are closed and spill back valve is open in the same time
3 Spill back valve is design to recycle all gas discharge gas
4 Size of suction system is large enough
They are condition can work without any problem

[motaleby]

Thank you all, see the below links please:

 

http://img.upload724...31386575571.jpg

http://img.upload724...02692727761.jpg

http://img.upload724...03308507009.jpg

[samayaraj]

Dear motaleby,

 

I could not see the above said link. Attach the sketch as PDF or other format here.

 

and the rest predicted the compression will be countiued untill Ps=Pd !

What do you think now?

 

I feel, Ps = Pd would never come unless the compressor is unloading.

 

#Samayaraj

[motaleby]

Sorry, I've uploaded it again:

 

http://filecloud.io/8pjlfax7

 

Thanks

Edited by motaleby, 05 February 2015 - 11:17 PM.

[Steve Todaro]

The suction and discharge shut down valves are typically fail closed. The recycle and blow down are typically fail open. If the valves have pneumatic operators, the situation above happens if air pressure is lost and the blow down valve hangs up in the closed position.

 

It is common to start reciprocating compressors that operate at elevated suction pressure with the suction valve closed and the bypass open. The discharge can be open or closed as the discharge check valve will prevent back flow and pressurization. Usually the blowdown is cycled open and closed to allow start with minimal mass in the loop.

 

If the condition in the above question is reached from a running status there will be more mass in the loop. The pressure on the discharge side will drop and the suction side pressure will increase. When the loop stabilizes the discharge will be higher than the suction by the delta P across the bypass valve and pipe. If it is a multi stage compressor, the suction side pressure may exceed a component MAWP and (hopefully) a relief valve will open.