What is the nominal size (DN) of a valve?

DN:

A combination of letters and numbers used to identify the size of piping system components. It consists of the letter DN followed by an integer number without a factor. This number is directly related to the characteristic dimensions of the end connection, such as the bore diameter or the outside diameter (expressed in mm).

Note:

1. Unless otherwise specified in the relevant standards, the numbers following the letters DN do not represent measured values and cannot be used for calculation purposes.
2. Those standards that utilize a DN marking system should give the DN in relation to the size of the pipe element, e.g. DN/OD or DN/ID.