900X emergency shut-off valve is a kind of valve used to allocate the direction of water supply in the water supply system where fire water and domestic water are connected in parallel. When a fire breaks out, firefighting urgently needs a lot of water, 900X emergency shut-off valve immediately cut off domestic water, to ensure enough firefighting water: when the water pressure of firefighting stop water decreases. The valve opens automatically and is normally open to restore the domestic water supply. The valve eliminates the need for a separate fire supply pipe network for the system, which greatly saves construction costs and water consumption. The valve control has high sensitivity, safety and reliability, easy commissioning and long service life.