Changing mm with DN for the pipes

[popescuflavius]

How can I change the measurement unit from mm to DN for the pipes  ? 

[iainsavage]

What do you mean?

DN means nominal diameter which could be in metric or imperial.

By DN, are you meaning inch sizes?

[popescuflavius]

Like here in the Belgium we use for the drain pipes PEHD Geberit ,
size like Ø 40,50,56,63,75,90,110,125,160, and i have but in mm and it s not a corespondence between mm and Ø.
For example in place of Ø110 i have 100 mm , and this is not what i want , and I can't change the size of the pipes because it s a plug in from geberit .
And for the heating pipes i want to have in place of the mm the DN (interior of the pjpe) and i know that is possible. Because the mm and DN they are not the same , I have problems when i try to insert a water valve on a pipe with the size in mm the messages with errors appear on screen "personal connection was created".

[iainsavage · Accepted solution]

OK, I don't know the conventions in Belgium but in UK it is usual to state plastic and copper pipe sizes based on outside diameter, steel or iron sizes based on nominal sizes.

The diameters that you listed are Outside Diameters of plastic pipes.

For tagging purposes you can edit the tag to use Outside Diameter as the tag parameter rather than Size. Same for schedules:

You can also edit the pipe segment sizes to make the Nominal Size equal to the Outside Diameter:

Whereas for steel pipe the Nominal Size doesn't equal either the Inside or Outside Diameter (it historically is roughly equal to a conversion from nominal inch sizes to mm e.g 1"=>25mm, 2"=>50mm, 4"=>100mm etc)

As far as pipe accessories and fittings are concerned the issue that you face is that the type catalogue or lookup table for the family will only have certain sizes, probably matching steel nominal sizes, so Revit will insert a taper if you try to connect a 100mm valve to a 108mm copper pipe. The way around this is to duplicate the 100mm type in the family but change the connector sizes to match the pipe diameters - so you'd have a type called say 100_108mm which would physically represent a 100mm valve but would have 108mm connectors. The mating flanges would also need to be duplicated in the same way so that there is no taper inserted at the flange.

Hope this helps but if I've misunderstoof what you need please reply back.

[popescuflavius]

Thank you very much for the detailed answer. That was indeed what I was looking for.