通徑在各國(guó)、各行業(yè)標(biāo)準(zhǔn)中都各有解讀。公稱通徑是一個(gè)圓整數(shù)它和實(shí)際通徑不*相同,它以不同形式的閥門和不同公稱壓力、不同規(guī)格尺寸來劃分為縮徑、不縮徑及全通徑、流通直徑。我國(guó)按GB/T12237、GB/T12238、GB/T7746來執(zhí)行。 
         美國(guó)的通徑劃分。按美國(guó)國(guó)家標(biāo)準(zhǔn)ANSI.B16.1；美國(guó)工程師協(xié)會(huì)ASME.B16.34；美國(guó)石油協(xié)會(huì)AP16D；標(biāo)準(zhǔn)以不同的壓力規(guī)定不縮徑的zui小流通直徑。 
         英國(guó)的通徑體系劃分以BS5351規(guī)定了球閥、通孔閥和不同的壓力等級(jí)劃分zui小流通直徑。
         日本的通徑體系劃分以JIS.2001規(guī)定了通用閥門、船用、室外下水道通用，以不同的壓力等級(jí)劃分流通直徑，以我國(guó)標(biāo)準(zhǔn)為例。 
  
There are different understandings for DN in different countries. It is an integer which is a little different from practical diameter.It is divided into reduced bore, non-reduced bore,full bore and flow diameter by different valve, nominal Preassure, spec sizes. It is carried out by GB/T12238、GB/T7746 in China.
American standard.ANSI.B16.1;ASME.B16.34;AP16D.
Inch system is applied to BS5351.
Japanese diameter system conform to JIS.2001.