a pressure relief valve with adjustable blowdown construction

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What is the meaning of blowdown?

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blowdown: the difference between actual popping pressure of a pressure relief valve and actual reseating pressure expressed as a percentage of set pressure or in pressure units.
好吧，没人给解释，那么就自己来解释吧。在ASME PTC25 Section2的2-7中有如上之英文解释。找了好久才找到的。那么VIII-1之UG125到UG140里面的关于这个BLOWDOWN是怎么翻译的呢？adjustable blowdown construction在2010中文版的规范里翻译为可调排污结构是否值得商榷呢？希望高手释疑。