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     ͨ���ڸ��������ИI(y��)��(bi��o)��(zh��n)�ж����н��x�����Qͨ����һ��(g��)�A����(sh��)���͌�(sh��)�Hͨ������ȫ��ͬ,���Բ�ͬ��ʽ���y�T�Ͳ�ͬ���Q��������ͬҎ(gu��)��ߴ�턝�֞�s�������s����ȫͨ������ֱͨ�����҇���GB/T12237��GB/T12238��GB/T7746���(zh��)�С�
     ������ͨ�����֡����������Ҙ�(bi��o)��(zh��n)ANSI.B16.1���������̎��f(xi��)��(hu��)ASME.B16.34������ʯ�ͅf(xi��)��(hu��)AP16D����(bi��o)��(zh��n)�Բ�ͬ�ĉ���Ҏ(gu��)�����s������С��ֱͨ����
     Ӣ����ͨ���wϵ������BS5351Ҏ(gu��)�������y��ͨ���y�Ͳ�ͬ�ĉ����ȼ�(j��)������С��ֱͨ����
     �ձ���ͨ���wϵ������JIS.2001Ҏ(gu��)����ͨ���y�T�����á�������ˮ��ͨ�ã��Բ�ͬ�ĉ����ȼ�(j��)������ֱͨ�������҇���(bi��o)��(zh��n)������
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.