Overpressure Relief Valves

Overpressure Relief Valves

Overpressure Relief Valve is a one-way valve designed to open automatically to prevent accidental overinflation of a BC’s Air Cell. Can usually be manually activated by means of a pull cord and, as such, can also function as a remote exhaust.

Separators, Storage Tanks, Heat Exchangers, columns and certain piping segments etc. are designed to handle certain operating pressure. However combination of a variety of causes may lead to over pressure in these equipment which may exceed the maximum allowable working pressure (MAWP) value. Overpressure relief valves are used to relieve the pressure in these equipment before it can cross the maximum allowable working pressure, thus protecting the equipment from damage. The overpressure relief valve set point should be such that relief valve will open before the maximum allowable accumulated pressure (MAWP) is reached in the vessel. For this purpose usually a hydraulic calculation should be done for overpressure relief valve discharge line to determine the back pressure at Relief Valves, which on addition to the pressure drop across pressure relief valve gives the pressure accumulation the equipment.

The overpressure relief valve size is based on a minimum relieving flowrate which can prevent the build up of pressure in the protected equipment from exceeding the MAWP limit. For several possible causes of over pressure in the vessel, relieving flowrates are calculated and the maximum of these flowrates is selected for overpressure relief valve sizing. The over pressure cause corresponding to this flowrate is then known to be the governing case for pressure relief valve sizing.