How a pressure reducing valve works

The pressure reducing valve maintains a constant water pressure at the outlet. That is, it stabilizes the water pressure downstream in the direction of flow.

The water pressure before the valve may vary, but the pressure after the valve remains stable. If there is no water pressure in the pipeline or it is lower than the set pressure of the pressure reducing valve, the valve will remain fully open.

When the pressure in the pipeline rises above the set value, the shutter of the pressure reducing valve will close as much as necessary to keep the downstream pressure constant.

On one side of the valve stem, there is a shutter that blocks the flow passage, while on the other side, there is a piston.

The piston is pushed on one side by a spring that tries to open the valve. On the other side, the piston is pressed by water from the outlet of the pressure reducing valve. The water pressure force attempts to close the valve.

As long as the spring force is higher than the water pressure, the valve remains open. That is why these valves are also called 'normally open'. As soon as the water pressure on the piston exceeds the spring force, the piston moves and blocks the flow passage.

The pressure reducing valve can operate in fully open, fully closed, or partially open modes. The position of the valve shutter is determined by the balance of forces on the piston between the water pressure and the spring force.

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