API-RP-576

Some relief valves are manufactured with resilient O-rings or other types of soft seats to
supplement or replace the conventional metal-to-metal valve seating surfaces. Usually,
the valves are similar in most respects to the other pressure-relief valves, with the
exception that the disks are designed to accommodate some type of resilient seal ring
to promote a degree of tightness exceeding that of the usual commercial tightness of
conventional metal seats. Figure 3 illustrates one type of O-ring seat seal as installed in
a safety-relief valve.
4.4.2 Applications
Relief valves are normally used for incompressible fluids (see API 520, Part 1).
4.4.3 Limitations
Relief valves should not be used:
• in steam, air, gas, or other vapor services;
• in installations that impose any backpressure unless the effects of the backpressure
have been accounted for;
• as pressure control or bypass valves.
Fion Zhnag/ Charlie Chong