A pressure relief valve is a safety device designed to protect a pressure vessel (or system) under conditions that increase pressure in that vessel (or system), beyond the stated design pressure or maximum permissible working pressure (MAWP). A relief valve's primary function is to preserve life and property by venting fluid from an over-pressurised pipe.
A pressure relief valve usually comprises three functional components:
A Valve
A sensing element (like a diaphragm or a piston).
And, an associate force element (like a spring).
In ordinary designs, the poppet on the valve contains an elastomeric seal; while, in high-pressure systems, a thermoplastic seal, whose function is to create a seal on a valve seat.
For Sensing Element, the piston-like design is useful for higher relief pressures are needed, or if there is a rugged medium. The diaphragm is a preferable choice for a low-pressure system (but that requires high precision).
Under the normal operational condition, the relief valve remains usually closed; until pressures upstream reach the desired set pressure. Then, the valve will crack open when at the threshold pressure, and then continue to open as pressure increases. When upstream pressure falls a few psi units below the threshold pressure, the valve will close again.
The pressure relief valve needs to be opened at a predetermined fixed pressure and shall flow at a specified overpressure with rated power. It must be closed when the system pressure has returned to a safe level. It must also get equipped to work on various fluids and fluid phases in a consistently smooth and steady manner.
Comments