Centrifugal Compressor capacity & head

[naturalgas01]

Recently i have been working on compressor performance calculation, and this is first time i am working on compressor.
I know that increase in suction pressure increases compressor capacity,acfm. As suction pressure increases, we are on left side of the performance curve so actual volume going to compressor is low.(am i right!)So, actual cfm going to compressor is low and compressor will have more capacity available.

now, i am confused for how decreasing polytropic head will increase compressor capacity ? Because when head goes down, we are operating on right side of the curve and compressor doesn't have capacity available to compress more gas? Am i going on right direction?

please explain with engineering equation.

thanks
naturalgas01

 

[chicopee]

What type of compressor are you working with?

 

[naturalgas01]

chicopee,

it's a Centrifugal Compressor

 

[chicopee]

Capacity of a compressor is based on piston displacement, speed of rotation and volumetric efficiency and not really on supply pressure.
Delivery and supply pressures are basically used to determined the horsepower (isothermal and isentropic) of compressors.I am not sure what you mean "as suction pressure(more appropriatly referred as supply presure) increases". Does that mean the pressure is getting higher or lower?
You are using the term "polytropic head" which should only be used when you are referring to the compression phase of a compressor thermodynamic cycle and not to the compressor capacity.
I would suggest that you get a mechanical engineering handbook such as Kent or Mark and read the sections on compressors so as to familiarize yourself with the enginnering approach to evaluate compressors. Particularly pay attention to the section on indicator cards which are used to determine compressor performance. These books are excellent