Working principle of the pressure regulator: When the pipe is fed water from the inlet end, the water flows through the needle valve into the main valve control room, and the outlet pressure acts on the pilot valve through the catheter. When the outlet pressure is higher than the set value of the pilot valve, the pilot valve is closed, and the control room stops draining. At this time, the pressure in the control room of the main valve rises and closes the main valve, and the outlet pressure no longer rises. When the outlet pressure drops to the set pressure of the pilot valve, the pilot valve opens and the control room drains downstream. Because the displacement of the pilot valve is greater than the inlet water of the needle valve, the pressure of the main valve control room drops, and the inlet pressure causes the main valve to open. In the stable state, the water inlet and drainage of the control room are the same, the opening is unchanged, and the outlet pressure is unchanged. Outlet pressure can be set by adjusting the pilot valve spring.