Reciprocating compressors work according to the positive displacement principle.
The periodic change in volume of the working chamber is carried out by a piston which moves on a straight line. The change of volume can also be carried out via an oscillating diaphragm (diaphragm compressor).
Besides the oscillating compressors there are compressors with rotating or orbiting displacement (rotors or revolving pistons) which are called rotating piston compressors.
The figure below shows the schematic build up of a reciprocating compressor. The piston (2) with the diameter dK moves inside the cylinder 1 between the two end positions (top dead center DT and bottom dead center KT), with the stroke s. If there are working chambers on both sides of the piston (1a, 1b), the compressor is called double acting, as opposedto single acting.
The difference between the largest and the smallest volume of the working chamber is called the piston displacement Vh. The smallest volume is called the clearance volume Vo.
The medium to be compressed enters the working chamber and leaves it after the compression via the compressor valves (sunction valves E and delivery valves A).
The oscillating movement of the piston is obtained via the crank mechanism (consisting of piston rod 3, cross head 4, connecting rod 5 and crank 6).
Piston compressors for higher pressures or higher compression ratio are designed as multistage compressors, that is with several working cylinders working in sequence. The displacement within a stage can be split up into several cylinders working in parallel.