CFM rating of air compressor?

We have Double stage reciprocating air compressor of 35CFM. We are doubting about the capacity as it is not able to meet 33CFM at 6Kg/Cm2 Pressure. In this regard we are keen to caluclate the deliveri in CFM, But we don,t have Idia to calculate the same. Kindly provide some information to calculat.
Thanking you.

Reciprocating air compressor capacity (in terms of free air cfm) is determined by calculating the displacement cfm and multiplying by the volumetric efficiency. The displacement cfm for a two-stage machine is calculated by taking the cylinder swept volume of the first stage (only) and multiplying by the rpm. In your case the displacement cfm would be 3.25x3.25x0.7854x3x1000/1728 = 14.4 cfm if the pump were operated at 1000 rpm. Most two-stage compressors in this range are operated between 800 and 1200 rpm, so I would take 1000 rpm as typical. The volumetric efficiency can vary between, say, 80-95% depending on the exact design of the pump. I doubt it would be less than 80%. Therefore for a conservative estimate, I would put your pump at about 14.4x0.8 = 11.5, say 12 cfm. Working a two-stage up to a typical maximum operating pressure of 175 psig at this capacity would require something less than a true 5 hp motor. A true 5 hp (about 22 amps at 230 volts) can supply about 17 or 18 cfm at 175 psig from a well designed two-stage.

I have never heard of Wayne as a compressor manufacturer and I have no idea if any parts are available. You might try and locate them to verify that 175 psig is an acceptable safe max operating pressure though. Most two-stage machines are but you never know unless it is specifically stated.

Rod