Hi
Thanks Admiral, Kim, cnr6400, Kerrin and Mike
Chris, here's plan for the regulator
It relies on the disc being a perfect seal on the body, initially being held by the small spring and then by steam pressure.
When I was trying to do the hydraulic test I could not get it to seal. I tried lapping, increasing the spring pressure all to no avail.
Don't quote me on this ( I'm sure someone will let us know) but I would imagine that in full size the disc would be 9" or 10" in diameter and have plenty of surface area to seal.It could be it's one of those things that doesn't scale down very well.
The screw down type of regulator seems to be much preferred by model loco builders. To fit one these requires a large enough wet head bush on the front tube plate through which the regulator can be fitted. Unfortunately Conway has a smallish bush, not big enough to get a screw down type through.
Which brings us onto the ball valve which is now being favoured by many builders. Available in stainless steel for a £5 on ebay ready built.
So we will see if it works
Cheers
Rich