For a two stage reciprocating compressor, compression from p1 to p3 is with perfect intercooling and no pressure losses. If compression in both the cylinders follows the same polytropic process and the atmospheric pressure is pa, then the intermediate pressure p2 is given by

• p2 = (p1 + p3)/2
• p2 = p1.p3
• P2 = Pa x p3/p1
• p2 = pa p3/p1