HOLLOW rotary valves

[GC]

I've seen it in high-end trombones. Pop off the bottom rotor cap, and inside is a thin outer cylinder, a couple of bent pipes leading between valve ports, and a lightweight cap at the other end to carry turning force. It's a mostly hollow tube with some necessary inclusions. I've long wondered the same.

[Rick Denney]

I seem to recall the mention of hollow valves with respect to my early 80's Sanders (Cerveny), but I didn't sense particularly light valves on that instrument compared to, say, a Miraphone. I just don't remember their heft on the few occasions I had them out of the instrument.

Rick "not exactly exploring the limits of technique in those days" Denney

[tbonesullivan]

The Rotary Valves that Kanstul used as their 5th valves on their tubas were partially hollow. The inside of the Kanstul CR valve is definitely a bit interesting. Some other manufacturers use rotors that have "extra metal" removed, like the Meinlschmidt "open flow" valves.

[bone-a-phone]

I have the Kanstul 1662i bass bone with 2 CR valves. They aren't hogged out of a solid piece of brass, they are assembled from plate and tube. I had a little initial trouble with getting them adjusted, but since that, they have been great valves. Save a lot of weight in the overall horn.

[Wu299]

I've been thinking about this for a while as well. In my naive point of view it does not seem that difficult – to remove the large amounts of metal and leave just the tubes.

A much more complicated and precise machinery must be commonly done in other fields (where things don't even cost XX,XXX USD), right?

[timothy42b]

I've been thinking about this for a while as well. In my naive point of view it does not seem that difficult – to remove the large amounts of metal and leave just the tubes.

You just made every engineer react in horror.

Yes you CAN do that but when possible you avoid making things by throwing most of it away as waste.

[bone-a-phone]

I found an image of a Kanstul valve in rough shape over at the tbone forum. The valve was I think primarily developed for light weight, and manufacturing came second. Machine time is expensive, and to hollow this out on a machine would require fine work with small tools, which is all the more expensive. A brass shop does a lot of soldering and lathe work, so putting this together with solder then spinning it on a lathe was probably the cheapest way to go.

[iiipopes]

Did Hirsbrunner ever make hollow valves, or am I thinking of their composite valves that tended to expand and stick in the casings when warmed up?

[NCSUSousa]

According to a 1978 article reviewing the patent from Peter Hirsbrunner for the polymer valve, building a hollow valve from tube stock is more expensive than milling it from solid bar stock. https://asa.scitation.org/doi/abs/10.11 ... et="_blank See the right-hand column, first paragraph. Checking the actual patent application, his method was to build a polymer/brass combination bar and mill it using the existing machines to create a lighter weight valve.
Not sure if the cost statement is still true, but it seems most makers still use the same methods they did back in the 70s. Clearly Kanstul thought the light-weight benefit of the tube-stock method was worth showing off in their 'CR' rotor. Meinlschmidt still makes their 'carbon' rotary valve, and most others seem to still use the same machined solid brass.

Links related to building a valve from tube stock:
Piston Valve - http://www.dwerden.com/forum/entry.php/ ... rQmqGhKiHs
Rotary Valve (shop made by Dan Oberloh) - http://www.oberloh.com/gallery/rotaryva ... onpage.htm

Without the tools to mill valve from bar stock, I imagine that the built-up tube based valve is the only option. I also guess that with CNC control a milled valve can be produced from bar stock rather quickly and without much manual labor and must therefore cost less.

(Edit - Looked up the patent application referenced in my first link)

[pjv]

I have a Kanstul F with said CR valve with full bore ports. I can't really say that they feel any lighter than what Miraphone makes. How Miraphone seems to make such a quick valve and other manufacturers can't is a mystery to me.

[pjv]

So how does Miraphone produce valves which are quicker than the competition? MW is also a top notch company, but their valve are much heavier (at least that's how they feel to me)

[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]

deleted

[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.