The Home Machinist!

Isn’t the supply fitting on the Allen ten wheeler 1/4” not x 3/8” tube flare?

FYI,. I run 1/4 copper line after the Y pipe and i have no issues delivering more then enough steam to run like a scolded animal. if anything it helps when starting a long train with a light locomotive.
if you stop and think about it, the ID of the 1/4 copper is pretty close to the ID of the 1/8 npt pipe that feeds the cylinder castings
(Allen American and Ten wheeler)

Thanks Chris! I was considering comparing the I. D. s from throttle to cylinder to see if 1/4 copper tube would be suitable; now I will do it for certain.
Don Young did not leave very much room between the front wall of the saddle and the cylinder supply line; a commercial 5/16" Flare Nut (5/8" hex) does not fit! (To be fair, he did show, but not detail, some 1/2" Hex custom unions; I was trying to use off-the-shelf hardware instead.)
That is why I was asking if somebody had already worked out some more compact union fittings. (Thanks again Fred V.!!!) The Fred V. [Bill Van Brocklin] 1/4" fittings (7/16" or 1/2" Hex Nuts) should fit with room to spare...

Kimball

I see where you went with this, thanks. - David