PRV stability, inlet pressure drop and built-up backpressure, should be evaluated at the rated capacity of the PRV. The rated capacity of the PRV corresponds to a specific overpressure, which is 10% of the set pressure or 3 psi, whichever is greater, for ASME VIII certified relief devices. Evaluating PRV stability at overpressure other than that for which the PRV is certified may lead to missed opportunities for improvement. Whether designing new or evaluating existing pressure relief systems it is important to use the correct basis for PRV stability (inlet and outlet pressure loss) calculations. Using the incorrect basis can raise concerns where there are none and, conversely, overlook potential concerns. A common miscue is using the allowable accumulation as a basis for PRV capacity calculations and subsequent stability analyses.
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