The main valve is composed of valve body, valve plate, valve cover, valve seat, piston and piston cylinder. The external control component is composed of filter, regulating valve and control valve. When the downstream flow is lower than the set flow, the control valve connected to the outlet of the main valve opens, and the pressure water in the control room of the main valve flows into the outlet of the main valve through the filter, the regulating valve and the control valve, and the main valve plate rises to increase the flow. When the main valve outlet flow is higher than the set value, the control valve is closed. A part of the pressure warm water at the inlet end of the main valve enters the control room of the main valve through the regulating valve and the filter, causing the pressure in the control room to increase and the main valve plate to drop, thus reducing the downstream flow of the main valve. The control valve can adjust the flow downstream of the main valve.

1. Valve body 2, large valve plate 3, needle type regulating valve 4, ball valve 5, pressure gauge 6, sealing ring 7, adjusting screw rod 8, cylinder head
9. Piston 10, valve stem 11, valve seat 12, pressure gauge 13, ball valve 14, regulating ball valve

The pilot valve above the valve can be set at a fixed flow rate in advance when it is installed in the water transmission and distribution pipeline, so that the pressure in the upstream of the main valve will change without affecting the downstream water volume.