Piping and Fittings

[triton]

I am currently making up the manifold on my loco, which calls for a 3/16" x 40 threads on the manifold ends, with a pipe size of 1/8". 

What size union nut is used? All the suppliers have 1/4" x 40 for 1/8" pipe or 3/16" x 40 for 3/32" pipe with pipe nipples to match. Do I need to make a special one or do I change the thread size on the end of the manifold??

Suggestions or recommendations would be appreciated.

[springcrocus]

The tapping drill for 3/16" x 40 is 5/32" so it doesn't leave much room to create a flange or olive for 1/8" pipe. I suspect you will have to go up to a larger size nut, either 7/32" or 1/4". I don't, however, recall seeing 7/32" x 40 nuts supplied commercially so if you want that size, you would (most likely) need to make your own.

Regards, Steve

Mods - you might wish to move this thread to "General Chat"

[mbrown]

I make my own nipples to go on a 1/8" pipe and fit inside a 3/16" x 40 union nut. The thing is to make the nipple so that it only has the coned bit and no "sleeve" so that the hole in the nut can be 1/8" clearance.

They are a wee bit fiddly to silver solder in place, but a small ring of 1 mm solder allows it to be done neatly enough.

Malcolm

[kipford]

7/32-40 nuts for 1/8 pipes are available from Macc Models, I have some at home.

Macc Models

[Gary L]

Apr 11, 2022 21:45:57 GMT mbrown said:

I make my own nipples to go on a 1/8" pipe and fit inside a 3/16" x 40 union nut. The thing is to make the nipple so that it only has the coned bit and no "sleeve" so that the hole in the nut can be 1/8" clearance.

They are a wee bit fiddly to silver solder in place, but a small ring of 1 mm solder allows it to be done neatly enough.

Malcolm

I agree with Malcolm. Where space is tight, this is the way to go, and a perfectly respectable engineering solution. Some people make all their pipe joints this way, feeling that the full cone method is wasteful of space and clumsy in appearance. I wouldn't go that far, because there is no denying that cones are fairly foolproof, whereas a nipple can be a bit of a fiddle to fit square, but they will solve your problem.

Another method is to make a flare, but that requires extra tooling.

Gary

[92220]

Another way to save space, where space is tight, is to use coned fittings with a splayed end pipe. The fittings can be made considerably smaller than with nuts and olives.

Bob.

[triton]

Many thanks for all the help and suggestions.