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[ASME CODE REQUIREMENT]
2

[ASME CODE REQUIREMENT]

[ASME CODE REQUIREMENT]

(OP)
Dear All,
Is there any reason to continue with open bonnet pressure relief valve for air service? Do we have such a requirement in ASME?
regards,

RE: [ASME CODE REQUIREMENT]

Hi. ASME has no issue using open bonnet for air service, although the usual/expected observations should be noted (back pressure, spring protection etc).

Per ISO, only the term Safety Valve is used regardless of application or design.

RE: [ASME CODE REQUIREMENT]

There is NO ASME Requirement for an Open Bonnet PRV on Air, just a lifting Lever. The Bonnet (open or enclosed) houses the spring.

Per ASME Section VIII, Division 1, Paragraph UG-136(a)(3), "Each pressure relief valve on air, water at the valve inlet that exceeds 140°F (60°C), excluding overpressure or relief events, or steam service shall have a substantial lifting device which when activated will release the seating force on the disk when the pressure relief valve is subjected to a pressure of at least 75% of the
set pressure of the valve."

Notice ASME uses the generic term Pressure Relief Valve. In ASME, a Safety Valve is used for compressible fluid, typically steam or air. Typically the Safety Valve has an Open Bonnet with a visible spring. Conversely, a Safety-Relief Valve has a Closed Bonnet so that can be used for compressible or incompressible fluids. Typically, incompressible fluids do NOT have a Lift Lever, unless it is hot water as defined by UG-136(a)(3) as mentioned above. The Relief Valve is primarily for Liquid (incompressible) fluid. I hope this is helpful.

JAC

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