What is the necessity of multistage compression.......

Necessity of multistage compression i) As index of compression ‘n’ increases it increases compression work. ii) Increase in pressure ratio (P2/P1) it increases work as well as size of cylinder. iii) Increment in pressure ratio (P2/P1) beyond certain limit, volumetric efficiency decreases while it increases leakage loss on either sides the piston and valves. Due to above pointes and for higher pressure ratio compressor needs multistaging.

Fig. shows arrangement of two stage reciprocating air compressor with inter cooler and its working shown on P.V. diagram plane. Processes occurred in the cycle  - 1 – 2 – suction process by LP cylinder to draw atmospheric pressure  - 2 – 3 – compression process by LP cylinder up to pressure P2  - 3 – 4 – delivery of compressed air into the air cooler  - 4 – 5 – during this process air rejects the heat to the cold water and at the same time suction process by HP cylinder to draw air from air cooler.  - 5 – 6 – compression pressure by HP cylinder up to required pressure P3  - 6 – 7 – delivery of compressed air at required pressure to the point of use. This completes the process and system has shown saving in work shown by shaded portion.