|The compressor diagram for displacement compressors Figure A (at the bottom of this page) illustrates a theoretical compressor diagram and figure B illustrates a real compressor diagram for a piston compressor. The stroke volume is the cylinder volume that the piston travels during the suction stage. The clearance volume is the area that must remain at the piston?s turning point for mechanical reasons, together with the area required for the valves, etc. The difference between the stroke volume and the suction volume is due to the expansion of the air remaining in the clearance volume before suction can start. The difference between the theoretical p/V diagram and the real diagram is due to the practical design of a compressor, e.g. a piston compressor. The valves are never fully sealed and there is always a degree of leakage between the piston and the cylinder wall. In addition, the valves can not open and close without a delay, which results in a pressure drop when the gas flows through the channels. Due to reasons of design the gas is also heated when it flows into the cylinder.