Compressor Discharge PSV Set Pressure Basis

[ChemEngSquirrel]

I have a PSV on the discharge side of a reciprocating compressor. The set pressure of the PSV ensures piping and compressor cylinder design pressure limits are not breached. However, if the PSV lifts then rod loads will be exceeded due to the higher compression ratio and compressor motor power will also be exceeded.

In addition to limiting discharge pressure to below design pressure, should i be considering lowering the PSV set pressure to also avoid exceeding:

1) rod load limits
2) electric motor rating

Thanks.

 

[Latexman]

What are the design safety factors associated with your rod load limits and electric motor rating? Compare those to the
design safety factors of your piping and compressor cylinder. Also, your electric motor may/should have it's own overload protection. Just some things to think about.


Good luck,
Latexman

Technically, the glass is always full - 1/2 air and 1/2 water.

 

[zdas04]

Wait a minute here. You have a compressor running, not approaching rod load, not approaching a temperature setting, just under MAWP. Then pressure spikes a bit and hits the PSV set point. That is then new discharge pressure of the machine (possibly with some minor accumulation, but probably not) which would still not be in rod load (since it was not in rod load just before the PSV lifted).

If you were approaching rod load at normal operating pressure (call it 70% of MAWP), then you would definitely be in rod load when the PSV goes off, but that is a fact of the magnitude of discharge pressure not PSV setting.

David Simpson, PE
MuleShoe Engineering

Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat