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What is the blowdown of a Section VIII or non-code safety valve?

April 26, 2017blowdown non-code safety section valve VIII

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What is the blowdown of a Section VIII or non-code safety valve?

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The ASME Boiler and Pressure Vessel Code does not have blowdown requirements for Section VIII (or non-code) valves. Blowdown may vary from less than 2% to more than 50%, depending on many factors including: valve design, dimensional tolerance variation, where the set pressure falls in the set pressure range of a spring, spring rate/force ratio, warn ring/guide settings, etc. Typical blowdown for most valves is 15% to 30%, but cannot be guaranteed.