It is a combination of a vane pump with an oil-gas separator cast by aluminum alloy, small light. The pump is a vane pump with a locating ring. There is no high-pressure space in the oil-gas separator and there is a returning floater system in the normal pressure space. The vent pipe also has centrifugal effect. The high-pressure connecting pipe, the discharging valve, and the bypass valve are all in one shell. Under the pressure in the pump, the oil flows through the high-pressure connecting pipe. The discharging valve enters the metric exchanger, pushes four pistons to reciprocate and discharge oil in fixed volume. At the same time, air vents from the vent hole and a little oil accumulates in the normal pressure space. When the surface of oil increases to a certain height, the returning floater will float up and some oil will return to the low-pressure space in the pump. The operating pressure of the pump can be adjusted by.