True, I'm sure there will be some sort of sealent we can use, it just doesn't seem the best design,
Another point is that when using it, there is a bit of flex in the rod that connects from regulator handle to the valve so it doesn't feel very positive when closed if you know what I mean, there's a bit of spring in it, suppose could get around this by having some sort of quadrant at the handle / lever end with a positive stop on it.
I prefer the sweet pea design and the one on another 5" gauge engine I had which has the valve situated external to the boiler where the handle is with a poppet type valve. Sweet pea doesn't have a steam dome but the other did, it collected steam from a pipe in the dome, transferred it back to the back plate and back to the front plate again. I am sure Curley has his reasons for putting the valve in the dome though, probably to give the steam a shorter route and less chance of condensation or something.
anyway, good work on that. I think I might have to lap the faces on mine and make sure the spring is strong enough too.
Nick