Equations for piston valves

[Tubaing]

Can someone tell me the equations for measuring the correct thickness for valve bumpers?

[Dan Schultz]

Can someone tell me the equations for measuring the correct thickness for valve bumpers?

Since you said you are speaking of piston valves... there really isn't any formula except you have to have enough spacers under the cap to align the ports when the piston is up and though spacers under the finger button to align the ports when the piston is down. There's really no 'magic equation'.

The first thing you should do is determine that the stems are all the same length... the fingerbuttons are the same... and the top caps are matched.

I use a fiber-optic scope to 'look' at the port alignment. Sometimes you can get a direct line through the leadpipe or by pulling a slide. But, often I have to use a 45 degree mirror and pull a piston to look through the ports of the piston on either side.

I rarely rely on 'what's supposed to be in there' because quite often things have been changed through repairs. By using optic alignment gadgets you can see EXACTLY what's going on inside the valves.

[Tuba Guy]

I am working on this for my Martin (I need to align my York's valves, but I figured it was better to do it on a horn that I know isn't my #1...and is also the biggest, so I can see most easily).
I have put enough felt under the valve cap so that when the valve is up, it is alligned. However, when I push down the valve, there isn't enough space for the valve to go down. If I unscrew the fingerbutton most of the way it falls into place, but obviously, that isn't a very logical way to play (I'm not much for having parts fall off the instrument while performing...it gets annoying). Is there something completely obvious that I am missing, or if not, how would the people who actually know what they're doing go about fixing this problem?

[Dan Schultz]

I am working on this for my Martin (I need to align my York's valves, but I figured it was better to do it on a horn that I know isn't my #1...and is also the biggest, so I can see most easily).
I have put enough felt under the valve cap so that when the valve is up, it is alligned. However, when I push down the valve, there isn't enough space for the valve to go down. If I unscrew the fingerbutton most of the way it falls into place, but obviously, that isn't a very logical way to play (I'm not much for having parts fall off the instrument while performing...it gets annoying). Is there something completely obvious that I am missing, or if not, how would the people who actually know what they're doing go about fixing this problem?

This is a common problem when working on older horns. Someone has changed the fingerbuttons, valve caps, or the stems at some point. That's why I rely only on optical alignment instead of "what's supposed to be in there".