900X emergency shut-off valve, is a parallel for the fire water and living water supply system for the deployment of the water supply valve direction. When a fire occurs, the fire needed a lot of water, 900X emergency shut-off valve immediately cut domestic water to ensure adequate fire water, fire fighting stopped when the water pressure decreases, the valve automatically opens, showing a normally open state, restore domestic water supply. The valve allows the system without a separate dedicated fire alone water supply network, greatly saving construction costs and water consumption. A valve to control high sensitivity, safe, reliable, easy to debug, long lifetime.