1.7.16

2" shaft mounting Pt11: When is a DN50 flange not a DN50 flange?

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The very pretty DN40-48.3 flanges turned up today but the bores were far too small at 42.4mm despite the flanges being marked 48.3mm. The 48.3 dimension refers to the exterior of the neck. Which I did not know when I placed my order.

Half the tapered flange neck would have vanished by the time I had bored the flanges out to 50mm. The next common size up is the DN50 which has a nominal dimension of 60.3mm. However, the bore is a couple of millimeters over 50mm at about 52.5.  I have emailed the supplier for further advice.

I have now discovered another flange which is much closer to a 50mm bore. Neck flange DN50-56.8 is sometimes listed as DN50-57. Sadly the supplier has been very slow to respond to my request to order new flanges and the return of the originals. It is just possible that this is due to the [unofficial] Danish national holidays so I shall just have to be patient. The problem is that I cannot make any real progress without them.

Many of the Danish suppliers seem to act as online agents for the main supplier, Indura. Unfortunately Indura will not deal with private customers via email. Presumably to avoid excessive need for technical support. The strange thing is that the main supplier has dimensioned drawings of their flanges on their website but never seem to quote the bore size. The precise bore size probably has little or no relevance to their usual customer. The standard sized connected pipe is welded over the extended neck and matches the bore size of the pipe itself.

But surely, denying the bore size to public view only increases demand for that information to be published? The mere fact that there are two different DN50 flanges suggests that there must be some demand for them both. Even if the DN50-60.3 is the "standard" variety the DN50-56.8 must have some purpose in order for it to be listed. A mismatch is obviously undesirable to avoid turbulence at a stepped bore.

Even if the final bore size proves to be 50.2mm then Loctite 638 may still not be stiff enough according to my responder on the CN ATM thread. It seems I must have the flanges welded on anyway. Albeit in reverse orientation to normal and with a solid shaft passing through the flange bore.

Click on any image for an enlargement.

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