Two stage reciprocating air compressors consist of two cylinders. One is called low-pressure cylinder and another is called high-pressure cylinder. When piston in a low-pressure cylinder is at its outer dead centre (ODC) the weight of air inside a cylinder is zero (neglecting clearance volume), as piston moves towards inner dead centre (IDC) pressure falls below atmospheric pressure & suction valves open due to a pressure difference. The fresh air is drawn into the low-pressure cylinder through air suction filter. This air is further compressed by piston and pressure inside & outside the cylinder is equal, at this point suction valves closed. As the piston moves towards ODC compression of air took place, then delivery valves open & this compressed air is then entered into a high-pressure cylinder through the intercooler. This called low-pressure compression. Suction valves of a high-pressure cylinder open when the air pressure in a high-pressure side is below to the receiver pressure & air from low-pressure cylinder drawn into the high-pressure cylinder. As piston moves towards the ODC, first stage air is further compressed. When air pressure from the low-pressure cylinder and inside the high-pressure cylinder is equal, suction valves closed. Now the air is further compressed by piston until the pressure in the High-Pressure Cylinder exceeds that of the receiver & discharge valves open. This desired high-pressure air is then delivered to a receiver.