pipe sizes!!!

[spamcanman]

I am new to model engineering and recently purchased a lovely 5" loco it had a home made injector which has been a problem so I am replacing it with a Chivers 16oz injector.
A simple job like this is proving a problem for me I am having to change the pipe from the clack to the new injector as the old pipe diameter is smaller than the new injector nipple. I have purchased a new length of pipe and now found the wall thickness of my new pipe is a lot thicker than the old, have I bought an odd size? Can somebody tell me what sizes copper pipe is sold please I am a metric guy and all these 1/8,3/32/5/16 is driving me crazy is nothing sold in millimeters.

[AndrewP]

Hi spamcanman and welcome to a fascinating and frustrating obsession pastime.
You can get metric copper pipes but they probably won't exactly fit your other bits which are likely imperial.
There is a list of sizes of copper pipe here and a useful conversion table here , in fact the whole of the second link is well worth reading.

Most of the tube sold for ME use seems to be thick wall but looking at the bursting pressures in the above link I don't know why - in the thousands of psi all of them!

Cheers, Andy

[baggo]

Most of the copper tube available from ME suppliers does seem to be imperial (ok for us old f*rts still living in the past ) but if you shop around you can get much thinner wall than the 'standard' 22swg (0.028"). EKP Supplies for one go down to 26swg (0.018") wall which, when dealing with smaller diameter pipes, makes a big difference in the actual bore. I see that Steamfittings also now stock lengths of the thin wall tubing.

As Andy says, most of the pipe fittings such as nipples etc. are made to suit imperial sized pipe.

John

[Boadicea]

Just one thing to add - with the thicker walled stuff it is much easier to get a good looking bend without it collapsing.

[cotswold]

If you have to make compromises on pipe sizes then, in the case of injectors, it is always better to err on the side of larger bore and have as smooth a pipe run as possible.

In view of the difficulty that I find in getting satisfactory smooth and non-collapsing bends in thin-wall tubing my personal preference is to go for a larger size of thick wall and anneal it to 'butter soft' (bright red hot and air cooled). After you have bent it you will find that it has work hardened.