900X emergency shutoff valve is a kind of water supply system which is used for parallel connection of fire fighting water and domestic water. It is used to allocate the direction of water supply. When a fire occurs, the fire needs a large amount of water urgently. The 900X emergency shutoff valve immediately cuts off the domestic water to ensure adequate water for fire fighting. When the pressure of water for fire stopping decreases, the valve opens automatically and returns to the normal state of opening, thus restoring the domestic water supply. The valve makes the system need not set up a separate fire water supply network, which greatly saves the construction cost and water consumption. Valve control sensitivity is high, safe and reliable, easy to debug, long service life.