As a bit of history, the general consensus about Rotax valves is that don't really do what they say -- instead of maintaining 100% geometric volume through the valves, they actually just constrict the airflow differently than normal rotary valves (or something close to that). I'm not exactly clear about this, and frankly this was never a problem with my tuba -- it's as open and free-blowing as any tuba I've played, piston or rotary. Frankly, it's not at all like most rotary tubas, and there is NO real adjustment needed by the player to compensate for additional resistance or stuffiness in the low range.
The problem, though, is the mass of the valves. They are heavy and not nearly as fast as I would like. Because of the way the Rotax valves are designed, they have more metal (mass) and more surface area (drag) than normal rotary valves. I'll post a few photos later, but essentially the Rotax valve is like a "full circle" of metal around its circumference, instead of the "open scoop" shape of normal rotors. I'm sure there's probably a bit more to it than that, but that's the main idea.
Martin (and others) have recommended doing some surgery to my valves, to carefully cut the "extra webs" from each of the Rotax ports in the valves, thereby making it essentially like a "normal" rotary valve, with the normal "scoop" shape. End result will physically have less mass to it, and will cover less surface area. Possibly even some benefits to response...with the cumulative effects of changing all 5 valves...?
I'm very curious to see how it turns out! I don't think it will end up WORSE, but I am curious how much of an impact there will be. Anything will help, and if this is only Round 1 of modifications... then hey, I had to start somewhere!
It'll be a few weeks until I get the valves back from Martin and can pop them back in, so it'll be a little while until I post an update. In the meantime, I have a tuba with no rotors.
). But, that was a quick fix, and I was up and running very quickly afterwards.
