Baer PVAK - part 1

[cambrook]

There has been a lot of discussion here about Alan Baer's Piston Valve Alignment Kit, and I don't intend to revisit all of that. I bought the kit and fitted it to my new tuba with the sole intention of getting excellent valve alignment, and I couldn't be happier with the result. The tuba uses the MW "big valve" set and the pictures are all of the 4th valve, but the alignment issues were identical for all of the valves.

Through family contacts I got a colonoscope that was surplus to hospital requirements when they changed from Pentax to Canon. It lets me take both video and stills inside the tuba. I was surprised to discover how out of alignment the valves were on a brand-new instrument - particularly given the tuba plays excellently.

Here is the factory set-up, with synthetic cork and felt on the top of the valve and very thick soft felt under the cap; with the PVAK ready to install.

PVAK.jpg

This shows the valve in the resting position is too low because the synthetic cork under the lower felt is too thick. If you look carefully you can see a large drop of water that is pooled against the side of the casing at the bottom.

UP at rest.JPG

This is taken with me lifting the valve in it's UP position, compressing the synthetic cork to get the correct alignment. You can see how the water at the bottom is equally across the valve/casing join.
Traditional materials may "settle in" and compress to give good alignment after some time, but with synthetic cork I don't think this will happen. I'm surprised that MW didn't use a thinner synthetic cork under the felt at the top of the valve, the return pressure exerted by the spring is constant (not user-dependent) and the valves should be in alignment at the resting position. I think they should have used a similar combination under the valve cap (instead of the thick, soft felt) to give more consistency (shown later).

UP lifted.JPG

Due to the limit of 3 photos per post I have to split this into a series.