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Hi Kim,may be you can find an American source for this type of valve balls.https://www.bengs-modellbau.de/en/material/seals/157/grafi-sil-valve-ballsPerhaps this will solve your problem.A more complicated but sure safe way is an other design of the ball seat, not easy to machine because of a self made tool for this.See my picture below.Left side is the worst way to do it.Middle is better.Right side is the best way to do it for a stainless steel ball.
Hi Kim, not to interfere...I had the same problem with the 0-4-0 British locomotive I'd made.The valve ball in Achim's 3rd picture was what was wanted.I took a twist drill and ground the tip off to that shape.Something like this...(left is normal drill bit, right is ground down)| | | || | | || | | /| | /\ /But with the slash at a shallower (desired) angle.I'm thinking (at the size I used) the drill bit was a bit too flexible and/or wobbled.
I made some check valves at one time where the seat wad on a screwed in insert. To get the ball to seat you took it and the valve seat and rolled the ball around with the seat on top of it on a couple of sheet of newspaper. The ink and paper fibers got picked up by the ball and wore a seal on the seat. Washed everything off installed it and it worked.Gerald.