The bench set pressure (CDTP) has been appropriately compensated for superimposed backpressure, and.However, if the amount of variable superimposed backpressure is small, a conventional valve could be used provided: It further goes on to say in Sections 5.3.2.2 & 5.3.2.3, "Balanced spring-loaded or pilot-operated PRVs should be considered if the superimposed backpressure is variable. The actual spring setting can be reduced by an amount equal to the superimposed backpressure to compensate for this." API 520 Part I, Ninth Edition, Section 5.3.2.1 says, "Superimposed backpressure at the outlet of a conventional spring-loaded PRV acts to hold the valve disc closed with a force additive to the spring force.
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