Centrifugal Compressor capacity

[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

 

[BigInch]

Increasing suction pressure increases mass flow entering the compressor, thus power required to maintain the same head at increased flowrates goes up. If power cannot be increased, flow must decrease.

You can arrive at points on the compressor performance curve in two ways. Decreasing head and increasing flow, or increasing flow and decreasing head.

On the left side, at low flows, head is the predominate component of power. On the right side of the curve, flow is the predominate component of power. In either case, available power is the limiting factor.

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