Q: Relief Valve Blowdown I want to know about blowdown percentage we should consider for pressure relief valves in liquid, gas, vapor services. Is there any reference which gives the percentage of blowdown for different services? Medhi Poormehdipoor.email@example.com A: Blowdown (blowback) is the difference between the set pressure and the reseating (reclosing) pressure of a relief valve (Figure 1). It is expressed in percentage of the set pressure. Values of blowdown pressures are set by codes (ASME, API, NFPA) and their typical values range from 7% to 10%, while their lower and upper limits are typically adjustable from 2% to 20%. For a detailed discussion see Volume 1…Full Story
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