The air compressor drainage valve, also known as the sewage valve, is used to discharge the condensed water in the compressed air tank; Can be opened before the air compressor boot, drainage; If the air compressor runs continuously, it can also be opened under the boot condition, but when it is opened, it should be opened slowly, not all at once, as long as it is opened to the exclusion of water until all the water is drained, and then it can be closed. In the maintenance of air compressor, it also serves as a pressure relief valve to relieve the pressure in the gas tank. Quick blowdown valve not only has simple structure, good sealing, but also small volume, light weight, less material consumption, small installation size, especially small driving torque, simple operation, easy to achieve rapid opening and closing. The fast blowdown valve is directly dependent on the force produced by the medium pressure to help the mechanical load seal on the disc, the mechanical load on the disc is mainly from the compression spring, which is almost a fixed mechanical load. Although for compression springs, the loaded blowdown valve can be well sealed by adjusting the spring force, the differential sealing pressure must be strong enough to ensure sufficient sealing force to achieve a seal when the valve is in normal operation. The sealing pressure difference should also be less than the opening and closing pressure difference to ensure flexible opening.