Pressure reducing valves reduce the pressure of the inflowing water so that it comes out of the valve more slowly than it entered. They are used to reduce waste and to keep pipes from bursting when water enters a home under higher pressure from the municipality's water source. They are made out of sturdy material, such as brass, to withstand the force that they are constantly under.
Pressure reducing valves have several parts. The inlet and outlet ends are connected to the piping where needed. Other parts include a spring, a diaphragm, and a pintle. The spring and diaphragm are on the side of the valve, and the pintle moves in the middle to open and close the valve to relieve the pressure.
The inflowing water pushes against the diaphragm inside the valve. The spring is on the other side of the diaphragm, and when the water tries to force the diaphragm in one direction, the spring forces the diaphragm back the other way. This slows the flow of water so that it doesn't come out as quickly and, in doing so, evens out the pressure. The most common place to find pressure reducing valves is right after a water meter, which helps ensure that the flow of water into a house is even and won't damage pipes or fixtures.