The check valve (also called one-way valve or oil return check valve) in the oil circulation system of the screw air compressor plays a vital role. The main function of the check valve is to ensure one-way flow in the oil circuit and prevent the compressed air from flowing back into the oil circuit system, thereby avoiding energy waste or causing the head to "vomit oil" failure. When the screw air compressor is unloaded, the gas in the oil and gas barrel will be partially vented through the discharge valve to reduce the back pressure and reduce the no-load energy consumption. At this time, the minimum pressure valve acts as a one-way valve to prevent the compressed air in the pipe network from flowing back.

In addition, the check valve also helps to maintain the minimum pressure required for oil circulation during shutdown, which is usually 0.2~0.4MPa. The temperature control valve also plays an important role in cold machine startup. It allows the oil to circulate in a small cycle, that is, the lubricating oil in the oil and gas barrel is directly sprayed into the main engine after passing through the temperature control valve and oil filter, quickly supplying oil to the main engine, avoiding short-term oil shortage and dry friction of the main engine caused by untimely oil circulation.

In the oil circulation system of the screw air compressor, the check valve is usually integrated in the oil return pipeline at the bottom of the oil separator to prevent the separated oil droplets from being carried away by the compressed air again. If the oil return check valve fails, the gas in the air tank may be discharged through the pressure relief valve after the air compressor is shut down, which may cause the compressor to start repeatedly. Therefore, the normal operation of the check valve is crucial to the stable operation and maintenance of the screw air compressor.