3.3.3.1.3 In a conventional pressure relief valve application,
built-up back pressure should not exceed 10% of the set
pressure at 10% allowable overpressure. A higher maximum
allowable built-up back pressure may be used for allowable
overpressures greater than 10% provided the built-up back
pressure does not exceed the allowable overpressure. When
the superimposed back pressure is constant, the spring load
may be reduced to compensate for the superimposed back
pressure. In this case, it is recommended that the built-up
back pressure should not exceed the allowable overpressure.
When the downstream piping is designed within the above
back pressure criteria, no back pressure capacity correction
(Kb = 1.0) is required in the valve sizing equations, for gases
at critical flow or for liquids. When the back pressure is
expected to exceed these specified limits, a balanced or pilotoperated
pressure relief valve should be specified.
업무/Flare & PSV