HOLLOW rotary valves

[Rick Denney]

...
- Leaving material on the circumference of the rotor bodies (in order to leave only two round holes exposed per side) is going to add weight (as - again - there's more material left in place than with typical rotors...and - not only more material, but - material at the circumference, which is going to require more energy to get the rotor body rotating).

Without the shell, though, even the slightest partial engagement of the valve will port air to whatever the casing is open to--vents, loose bearings--whatever. The solid outer shell provides a seal against the casing, and so a partial engagement only leaks sound between the bugle and that valve branch. I think it will change the way the valve carves the sound in a legato passage, but that's just a theory.

But the shell can be pretty thin. To be non-structural, however, something fancy has to be done to firmly support the bottom bearing pin. I can think of a couple of ways of doing it, but which may add nearly as much weight as a thin shell (though perhaps not as much inertia). But they'll have to avoid the two ports touching, or nearly touching, where they meet in the middle of the valve, where I suspect tube-constructed ports are soldered or brazed together. That means some kind of a donut that goes around that contact point to provide a mounting point for the bottom bearing pin. But with a shell, the bottom bearing pin can be mounted on a plate on the bottom of the valve. I am sure that's how Cerveny made their hollow rotors.

Rick "noting that the rotors in his Hirsbrunner are heavy, but still pretty fast" Denney

[timothy42b]

a couple of things:

- The ports (openings) on a rotor body may be full bore size, but - if the diameter of the rotor body is less than 2X (actually 2X+) the bore diameter, it's pretty much impossible for the bore - through the entire porting - to be full...unless - somehow - the cutouts are wildly ovaled (as with short-action pistons).

Makes sense, but I'm not sure it matters. It might restrict air flow, but as I understand it to the sound wave a bend looks like an enlargement of the bore rather than a restriction. So a properly designed valve might have to have a reduced cross section that exactly matched the sharpness of the bend. If you did one of those goofy double piston valves the bend might not be very sharp, but a rotor must be.

Do we feel stuffiness due to air flow or sound wave flow? I don't know the answer, it may be a combination, but I lean towards sound wave.

[bort]

One maker's rotors - used on their rotary instruments (and only a small percentage of their instruments that reach the USA are their rotary models) are quite heavy. Extra material is added (or left in place) in the circumferential area, which makes it appear as though those rotors feature round, full-bore porting. In fact, that circumferential added (or left-in-place) material actually constricts the bore of the porting more than with a regular rotary valve. Strong springs are required to drive those rotors at acceptable velocity. fwiw, that manufacturer - at least, in the past, has made a big deal about those rotors.

I had Martin Wilk cut down my rotors from said manufacturer, to remove that extra material. Result was quicker action, more open blowing, and all around "better".

Between the original valves and the stock linkages... That manufacturer does a pretty "meh" job of rotary instruments. If the ergonomics of that tuba had been good enough for me to keep it (otherwise a very nice tuba), maybe it would have been cheaper to just replace the whole valve set with a new Meinlschmidt or Voigt section and linkages.

[anotherjtm2]

...
Further, people seem to think of (in particular) brass instruments as "air flow" instruments. Even with a trumpet, they ain't crap worth of air coming out of the bell. These are SOUND COLUMNS much more than "air-moving columns". There's air THERE, because - without air being there - there would be nothing to vibrate, and there would be no sound.
...

I just started playing trumped (one of my quarantine projects), and noticed right away that I have to exhale before taking a breath because so little air goes through the horn.

Another thing relates to the thread about 6/4 tubas and effort and and how many overtones are in resonance: after a practice session with the trumpet, with its bright focused sound, it takes a minute to get used to the tuba sound again. Even my smallish tuba feels muddy by comparison, for a minute.

[Art Hovey]

The interesting question not yet answered in this thread is this:
How does Miraphone make its rotors seem so light? Surely someone here has examined them?
I imagine titanium would be an ideal rotor material if it weren't so expensive and if its thermal expansion coefficient is not too much different from brass.

[peterbas]

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[Rick Denney]

The interesting question not yet answered in this thread is this:
How does Miraphone make its rotors seem so light? Surely someone here has examined them?
I imagine titanium would be an ideal rotor material if it weren't so expensive and if its thermal expansion coefficient is not too much different from brass.

Any clues to be gleaned from this brief footage?
https://www.youtube.com/watch?v=t4mSNSd014g&t=5m05s

No, these are standard solid machined rotors. The shell he is fitting the rotors into will become the casing.

To the question of why Miraphone valves seem better, I don't think that's necessarily true. I've wiggled a lot of rotary valves over the years, and some have felt heavier than others, perhaps without exact correlation to the quickness of the valves. But the differences have been as much about leverage as weight--how far is the pivot (or ball) on the stop arm from the center of valve rotation, how far the pivot (or ball) is from the center of paddle rotation, and how long the paddles are. Long lever arms will make the touch lighter, but will increase the paddle travel. Weak springs will make the touch lighter, but at the expense of reduced reliability in the absence of perfect cleanliness and lubrication.

My Hirsbrunner valves feel heavy and seemingly stiffly sprung, but they don't slow me down at all within the context of what my fingers can do (or not do) anyway. My B&S valves feel much lighter (and they are indeed smaller, though I don't think that's the main reason they feel lighter). I'll have to measure up the leverage and paddle travel.

A light valve will be more apt to bounce farther (on rebound, of course, when not driven by finger force), by the way--it takes less energy to change direction. But it also compresses the stop material less, but the mass should be the bigger effect.

Rick "or so it appears to me" Denney

[windshieldbug]

Every one I've talked to who had played through this kind of valve (Allen valve) said,
"It plays just like a regular rotor."

They do.
The advantages are two-fold; the "short action" also means smaller radius so that the valve mass is considerately less.
Less mass = lighter action, less distance = shorter action.

None of this is new; I have a 1915 York Althorn with built-up rotary valves; hollow like a piston valve but turn axially instead of vertically.

[iiipopes]

...and (having worked on quite a few) those rotor assemblies are VERY VERY well-made, but (seriously) not "that" well-made...and certainly don't REMAIN "that" well-made after a decade or two.

I thought you were going to say you saw the wear patterns in the rotors and casings when disassembled for cleaning and adjustment.

[peterbas]

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[Rick Denney]

I also Always found that hard to believe that the rotors didn't touch the casing since putting oil on the side seemed to make the rotors turn smoother.
Rotors can be well maid but the bearing system is still rather poor. A normal bicycle wheel with a simple ballbearing last a long time when you give it a spin, a rotor not so much.
And yes there are small ball bearings, I've just looked it up. They would probably work a lifetime whithout maintenance on a tuba.
https://www.minebeamitsumi.com/english/ ... _6218.html

The question is whether we really want a system with so little damping. With rotors that could spin for a long time, nothing would keep them from bouncing off the bumpers except the gooey fingers on the paddles, and those aren't always actually on the paddle when the bouncing occurs.

I think I want a little damping that a bit of bearing friction (and oil) provides. What I don't want, however, is for that friction to change in any way during actuation, even if just a bit of gritty feel or a hump that is not to the point of arresting the movement unintentionally.

But I also want field serviceability, and premade ball bearings have to be mounted somehow, either friction fit, requiring them to be driven out when removing the valve, or using fasteners that provide their own problems and costs. Rotors already require friction-fit parts that have to be driven out, and that's one of the main reasons they rarely get cleaned and serviced properly.

Rick "not arguing for the current system, but cautioning against overdesign not driven by actual requirements" Denney

[peterbas]

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[peterbas]

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