Safety relief valves are automatic valves used on system lines and equipment to prevent over pressurization. Most relief valves simply lift (open) at a preset pressure and reset (shut) when the pressure drops only slightly below the lifting pressure.
Above image shows a relief valve of this type. System pressure simply acts under the valve disk at the inlet of the valve. When system pressure exceeds the force exerted by the valve spring, the valve disk lifts off its seat, allowing some of the system fluid to escape through the valve outlet until system pressure is reduced to just below the relief set point of the valve. The spring then resets the valve. An operating lever is provided to allow manual cycling of the relief valve or to gag it open for certain tests. Virtually all relief valves are provided with some type of device to allow manual cycling.
How Safety relief valves Works?
Safety relief devices remain closed during normal service operation & have been designed to automatically release a certain gas flow out of the pressurized line through the safety relief valve, as soon as the pressure within the section to be protected will have risen to the preset pressure, safety relief valve gets opened.
Safety relief valve closes automatically as soon as the pressure decreases below the set limit.
Other types of relief valves are the high-pressure air safety relief valve and the bleed air surge relief valve. Both of these types of valves are designed to open completely at a specified lift pressure and to remain open until a specific reset pressure is reached-at which time they shut. Many different designs of these valves are used, but the same result is achieved.
Spring Loaded Pressure Relief Valve
Balanced Bellows Valves and Balanced Piston Valves
Safety Valve.
A safety Valve is a pressure Relief Valve actuated by inlet static pressure and characterized by rapid opening or pop action. (It is normally used for steam and air services.)
- Low-Lift Safety Valve
A low-lift safety Valve is a safety Valve in which the disc lifts automatically such that the actual discharge area is determined by the position of the disc. - Full-Lift Safety Valve
A full-lift safety Valve is a safety Valve in which the disc lifts automatically such that the actual discharge area is not determined by the position of the disc.
Relief Valve
A Relief Valve is a pressure relief device actuated by inlet static pressure having a gradual lift generally proportional to the increase in pressure over opening pressure. It may be provided with an enclosed spring housing suitable for closed discharge system application and is primarily used for liquid service.
Safety Relief Valve
A safety Relief Valve is a pressure Relief Valve characterized by rapid opening or pop action, or by opening in proportion to the increase in pressure over the opening pressure, depending on the application and may be used either for liquid or compressible fluid.
- Conventional Safety Relief Valve
A conventional safety Relief Valve is a pressure Relief Valve which has its spring housing vented to the discharge side of the Valve. The operational characteristics (opening pressure, closing pressure, and relieving capacity) are directly affected by changes of the back pressure on the Valve. - Balanced Safety Relief Valve
A balanced safety Relief Valve is a pressure Relief Valve which incorporates means of minimizing the effect of back pressure on the operational characteristics (opening pressure, closing pressure, and relieving capacity).
Pilot-Operated Pressure Relief Valve
A pilotoperated pressure Relief Valve is a pressure Relief Valve in which the major relieving device is combined with and is controlled by a self-actuated auxiliary pressure Relief Valve.
Power-Actuated Pressure Relief Valve
A poweractuated pressure Relief Valve is a pressure Relief Valve in which the major relieving device is combined with and controlled by a device requiring an external source of energy.
Temperature-Actuated Pressure Relief Valve
A temperature-actuated pressure Relief Valve is a pressure Relief Valve which may be actuated by external or internal temperature or by pressure on the inlet side.
Vacuum Relief Valve
A vacuum Relief Valve is a pressure relief device designed to admit fluid to prevent an excessive internal vacuum; it is designed to reclose and prevent further flow of fluid after normal conditions have been restored.