Figure: Two Stage Reciprocating air compressor
Construction and Working : It consists of two cylinders (L.P. and H.P.) with water cooled intercooler and air receiver. First of all fresh air is sucked from atmosphere in low pressure (L.P) cylinder during its suction stroke at inlet pressure P1 and temp T1.The air after compression in L,P cylinder ( I st stage ) from 1 to 2 is delivered to intercooler at pressure P2 and temp T2.Now air is cooled in intercooler from 2 to3 at constant pressure P2 and from temp T2 to T3.After that air is sucked in high pressure (H.P) cylinder during its suction stroke. Finally air after further compression in H.P. cylinder (ie second stage) from 3 to 4 is delivered by the compressor at pressure P3 & Temp T4.