what is the working principle of the pressure relief valve of the fire-pump?

 During the operation of the fire pump, the main pipe water flow direction is from left to right, and one control water enters the pilot valve control room. When the water pressure is less than the set pressure release value, the pilot valve spring thrust is greater than the water pressure, the pilot valve The flap is closed.

The other way to control the water through the throttle needle valve into the upper chamber of the main valve produces a static pressure, the pressure of the upper chamber and the pressure in the main channel are equal. Since the upper plane of the main valve flap is larger than the lower plane, the pressure of the upper chamber against the valve flap is greater than the thrust of the water in the main passage to the valve flap, so that the main valve is closed.

If the main pipe water flow pressure rises and exceeds the set pressure release value, the water flow pressure of the control valve entering the pilot valve control room increases, and the water pressure is greater than the spring thrust. At this time, the pilot valve is opened and the main valve begins to relieve pressure. Because of the throttle control, insufficient water supply, the upper chamber pressure of the main valve is reduced, the lower chamber thrust is greater than the upper chamber pressure, the valve flap is raised, and the main valve is opened to quickly relieve pressure.

Because the above process is completed in an instant, the indoor fire water supply system will not cause harm when overpressure occurs. If the water pressure of the main pipe continues to increase, the opening amount of the pilot valve will also increase, so that the pressure difference between the upper chamber and the lower chamber of the main valve is larger, the opening amount of the main valve is larger, and the system is relieved faster. Conversely, if the main pipe water flow pressure is reduced (such as when the number of indoor fire hydrants is increased or the number of open nozzles is increased), the pilot valve control room pressure is reduced, and the pilot valve opening amount is reduced. The pressure in the upper chamber of the main valve is increased, and the valve flap of the main valve is closed, so that the water pressure of the main pipe is stabilized at the system design pressure.