Photo of Wilden P1 - polypropylene 

Performance is a balance of the incoming air supply pressure and quantity (SCFM) verses the piping system resistance. 

As example -- when fitted with rubber diaphragms - 80 PSI air supply - would pump 8 GPM with 50 PSI and use 6 SCFM.   If the back pressure of the system were reduced, the flow would be increased.

As example -- when fitted with Teflon diaphragms - 80 PSI air supply - would pump 8 GPM with 52 PSI and use 10 SCFM.   If the back pressure of the system were reduced, the flow would be increased.

The use of a solenoid controller can provide for a fixed flow rate.