<Li> Pressure vacuum release valve (PVRV): A combination of a vacuum pressure and a relief valve in one housing . Used on storage tanks for liquids to prevent implosion or over pressure . </Li> <Li> Snap acting: The opposite of modulating, refers to a valve that "pops" open . It snaps into full lift in milliseconds . Usually accomplished with a skirt on the disc so that the fluid passing the seat suddenly affects a larger area and creates more lifting force . </Li> <Li> Modulating: Opens in proportion to the overpressure . </Li> <P> In most countries, industries are legally required to protect pressure vessels and other equipment by using relief valves . Also in most countries, equipment design codes such as those provided by the American Society of Mechanical Engineers (ASME), American Petroleum Institute (API) and other organizations like ISO (ISO 4126) must be complied with and those codes include design standards for relief valves . </P>

How does a water pressure relief valve work