Emptying valve of piston type air compressor

An emptying valve of a piston type air compressor relates to a piston type air compressor and comprises a casing, a valve plug, a spring ring, a sealing ring, an exhaust elbow, a nut, a radiating sheet and an exhaust copper tube. The emptying valve is characterized in that a thread is arranged at the lower end of the casing made of pure copper materials, a big end up through hole is arranged in the casing, the valve plug is arranged in the through hole and in a reversed-T shape, the sealing ring is arranged at the lower end of the valve plug, and the spring ring is arranged at the upper end of the valve plug. The thread arranged at the lower end of the casing is connected with the exhaust elbow of the air compressor, the exhaust elbow is arranged on the front portion of the air compressor provided with the nut and the radiating sheet, and the lower end of the exhaust elbow is connected with a cylinder cover of a main machine of the air compressor. The emptying valve is installed on a main machine port of the