The so-called air compressor is usually driven by a motor and driven by a belt. The belt drives the flywheel mounted on the crankshaft to rotate, and the crank drives the connecting rod into a reciprocating motion. The connecting rod and the cross head are connected by a cross head pin, and the cross head reciprocates on the settlement section. The hydraulic piston is mounted on the crosshead. The piston is sealed by a piston ring and reciprocates in a hydraulic cylinder. Each movement of the piston generates a fixed volume of lubricating oil, and thus drives the diaphragm to reciprocate. Lubricating oil acts on the diaphragm, so it is actually the compressed gas of the diaphragm.

Although there is also a piston dynamic seal in the diaphragm compressor, there are two obvious differences compared with the piston compressor. First, the piston ring seal is measured in oil and does not contact with the gas, so there is no gas leakage. Second, the piston ring is lubricated with lubricating oil.

The hydraulic oil in the compressor plays an important role in the air compressor, including lubricating moving parts, compressed gas, and cooling. The circulation of lubricating oil starts from the crankcase and the oil sump of the crankcase seat. Lubricating oil enters the inlet filter, usually lubricating oil is cooled by a water-cooled cooler. The lubricating oil then enters the mechanical oil pump and is filtered through the filter. Then the lubricating oil is divided into two ways, one way to lubricate bearings, connecting rods, etc., and the other way into the compensation pump, which is used to promote the movement of the diaphragm.

The function of the compensation oil circuit is to compensate for the leakage and return of lubricating oil in the membrane head during the compression process. But usually compared with the lubricating oil in the membrane head, this part of leakage is very small. In each cycle of the compressor, hydraulic oil pushes the diaphragm against the air disk. If the leaked lubricating oil cannot be replenished in time, the volume of lubricating oil will not only decrease, and the diaphragm will not be completely close to the gas disk. The increase of the straight clearance volume affects the performance of the compressor. Therefore, the correct compensation oil system is a key to ensure the performance of the compressor.

In order to adjust the lubricating oil in the oil lubricated compressor, a pressure regulating valve is usually installed. This regulating valve can control the pressure in the membrane head. The regulating valve is opened when the high pressure is set, and closed by the spring.