Constant RPM of Gas Compressor I would like to improve my understanding of gas compressors. If the compressor is moving at constant RPM, does it mean that it can only allow the same volumetric flow rate at all times? So the power will remain constant too by $P=VI$, and then voltage and current will varie. My question is why there are changes of pressure and flow rate entering the compressor. Could anyone provide me some good explanation, please? I would like to know why the pressure inlet for gas compressor is decreasing and I am wondering if it is related to flowrate (in MMSCFD) as the flowrate increases?
 A: I guess one reason why pressure and flow rate entering the compressor may vary is gas liquid contents vary, liquid is separated in the suction scrubber, so when more liquid is separated the less is pressure and flow rate at the compressor inlet.
A: Peter Solo, it looks like you are posting an engineering question related to the equipment that you see on your job.  Most employers (all that I have ever encountered) consider such information to be proprietary, and in my opinion, you are "walking on thin ice" regarding the engineering ethics and legality of the situation, because such information should never be released into the public domain without employer approval.  I strongly urge you to use caution if you want to remain employed.
To answer your question, you need to talk to a process engineer at your place of employment.  Process conditions upstream of your compressor (i.e., feed flow rate or composition changes, disturbances due to changes in the unit heat balance, etc.), and process control schemes and control scheme changes upstream of your process (e.g., operator setpoint changes), will strongly impact what is happening at your compressor because material balance disturbances will propagate downstream from their point of origination.
A: I don't know very much about gas compressors, but I would assume that if it is a piston based compressor moving at constant RPM then yes the volumetric flow rate would be constant. 
However, I would also think that the power is not constant because as the pressure increases there is more force on the piston during each stroke. The energy required during each stroke of the piston is given by the distance it travels multiplied by the force on the piston (E = d*F).
