Used on the pump outlet of a water supply system to prevent medium’s back-flow, water hammer and water shock. It has three functions as an electric valve, check valve and water hammer remover. It is capable of improving the safety and reliability of the water supply system effectively through integrating the technical principle of slow-open, speed valve, slow-close, and removing water hammer and preventing of both pump-starting and pump-stopping water hammer. The gate can carry out open-close automatically upon the operation rules of the water pump just by operating the pump to open or close electrically. 300X Slow-Closing Check Valves features by the big flow and small pressure loss, reliable sealing performance, easy installation, debugging and maintenance and long duration.