API-RP-576

4.8.2 Applications
Pilot-operated safety-relief valves are generally used:
a) where a large relief area and/or high set pressures are required, since pilotoperated
valves can usually be set to the full rating of the inlet flange;
b) where a low differential exists between the normal vessel operating pressure and
the set pressure of the valves;
c) on large low-pressure storage tanks (see API 620);
d) where very short blowdown is required;
e) where backpressure is very high and balanced design is required, since pilotoperated
valves with the pilots either vented to the atmosphere or internally
balanced are inherently balanced by design;
f) where process conditions require sensing of pressure at one location and relief of
fluid at another location;
g) where inlet or outlet piping frictional pressure losses are high;
h) where in-situ, in service, set pressure verification is desired.
Fion Zhnag/ Charlie Chong