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Set Pressure Tolerance for Pressure Relief Valves

Set Pressure Tolerance for Pressure Relief Valves

Set Pressure Tolerance for Pressure Relief Valves


The set pressure tolerance for pressure relief valves shall not exceed ±2 psi (15 kPa) for pressures up to and including 70 psi (500 kPa) and ±3% for pressures above 70 psi (500 kPa), Ref. ASME Sec. VIII, Div. 1-2019, Para. UG-134(d)(1).
My question is: Should this tolerance be understood to apply to the valve assembled and in operation? or applicable to bench testing? or both?


RE: Set Pressure Tolerance for Pressure Relief Valves

The tolerances stated apply to the installed valve, why should they be any different? You may well find that many manufacturers have their own tolerance levels that meet and are better than those stated by ASME.

Note that bench testing can only provide a set pressure test at ambient temperature, hence CDTP - Cold Differential Test Pressure is used, based on the manufacturers allowance for elevated in service/operating temperature, plus adjustment for conventional type valves with back pressure

*** Per ISO-4126, the generic term
'Safety Valve' is used regardless of application or design ***

*** 'Pressure-relief Valve' is the equivalent ASME/API term ***

RE: Set Pressure Tolerance for Pressure Relief Valves

Thanks for your answer. This is also my understanding.

Best regards.

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