Pressure reducing valve

For water

Domestic water PRV's are generally found between the mains water supply and a sealed water heating system, typically a space heating system or a sealed hot water system.

For gas

Gas Pressure Reducing Valves are found in the connection to all domestic gas cylinders; this is essential as the liquified petroleum gas in the cylinder is at a very high pressure.

Safety valve

Pressure reducing valves should not be confused with safety valves; the latter are valves which usually open at a pre-set critical pressure or temperature which is higher than permitted by the system, and they allow the gas or liquid to escape, usually to the atmosphere. Some safety valves, for example on an oil boiler, will shut off the oil supply in the event of a rise above a certain temperature, for example if a fire were to occur. Most safety valves are factory pre-set and normally should not be tampered with.