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The inlet pressure is divided into two opposite directions, one up above the piston, and the other down to the disk, piston and spindle. This means that the pressure for closing the valve and the pressure for opening the valve become nearly equal. Therefore a large float buoyancy is not needed to close the valve tightly.

There are two types of water pressure reducing valves, direct acting and pilot operated. Valves used on smaller piping diameter units tend to be direct acting valves. These are the more popular type of water pressure reducing valves. They have spring-loaded, heat-resistant diaphragm connected to the outlet of the valve. This spring holds a pre-set tension on the valve seat.

Water entering the valve from the inlet side is constricted within the valve body and directed through the inner chamber controlled by the adjustable spring-loaded diaphragm and disc. When downstream pressure equals the pre-set tension, the valve closes, and water cannot flow to the outlet side. When water is used downstream of the pressure reducing valve, the outlet pressure is reduced. When this pressure gets lower than the pre-set tension of the spring the valve opens allowing water to flow to the outlet side.

Pilot Operated Pressure Reducing Valves are used when greater flow is needed. A pilot valve equipped with a spring-loaded diaphragm, similar to that of the direct actuated pressure reducing valve, is connected to the inlet and outlet side of the main valve. It is also connected to the chamber above the diaphragm of the main valve. The pilot acts in a similar way to the direct actuated pressure reducing valve. The pilot senses minute changes in downstream pressure. When downstream pressure exceeds the preset tension of the spring in the pilot, the pilot closes. This causes the pressure above the main valve's diaphragm to increase causing the main valve to close.

When water is used downstream of the pressure reducing valve, outlet-side pressure decreases. When this pressure gets lower than the pre-set tension of the spring in the pilot, the pilot opens allowing water to flow from the diaphragm chamber of the main valve to the outlet side. This will cause the main valve to open, allowing water to flow to the outlet side of the main valve.