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I saw on pictures that the stem of these valves isn't in the center of the valve cap (it has a offset).
What is the reason for that and how can the valve cap be dismounted ?
Do these valves work by same principle like the normal stroke bottom sprung piston valves ?

Some answers were given in the second post down this thread:

viewtopic.php?t=1050

Others can be found here:

Conn bass instruments’ catalogue from December 1934. Thanks to the generosity of Rob Perelli-Minetti the YMPP project can present scans of a December 1934 Conn bass instruments brochure. 14 pages in B/W (1590K):

http://groups.yahoo.com/group/YorkMaste ... ochure.pdf

This scan presents a document, which is a gem for everybody interested in brass instruments' history.

Aside from instrument documentation you will find photos of tubas greats of the era. Plus a photo of a one-off combination of tuba and trombone made for a Chicago theatre.

And yes, you have to join the Yahoo group in question to get access to this scan.

Klaus

The short-stroke valves "ovalize" the air passages so the valve doesn't have to travel as far (hence, "short stroke"). While this minimizes the valve stroke, it does have a few drawbacks:

1) While an ovalized tube (think about a round tube that's been squeezed down) isn't as tall as the same round tube, it's much wider. This means that the valve diameter has to be larger to accomodate the same size tubing. (think about the valve cluster being made of cookie dough and imagine how it would change when squeezed). This means that the center of the valves are now wider apart, so to get the buttons within comfortable distance, the stems must be offset.

2) While an offset stem cures the reach problem (at least for 3-valve clusters), it means that the conventional tacquet-and-groove valve guide system won't work with the valves recieving force offset from the center. So Conn had to incorporate a valve guide pin attached to the cap that the piston moves on, to keep the piston centered. Since the guide pin is fixed in relation to the casing itself, a more involved 2 piece cap is necessary.

3) Because of the larger-diameter piston, the valve is heaver (the weight increases as the square of the radius , as opposed to increasing linearly with the height)

4) The valve requires more complexity in the shape of the knuckles (oval to round) and the whole assembly process of a valve cluster is quite a bit more difficult. I understand that the short-stroke valves are the major item that keeps UMI from pumping out 20K's like cookies.

5) Valve alignment is more critical--a small offset in the piston-to-casing distance occludes more of the port than a conventional valve. So if you've got SS valves on your horn, it's important that you have them checked regularly for cork and felt wear.

Conn wasn't the first with short-stroke valves--Holton had a version with ovalized ports in the 1930's. But Holton's design was very different and caused bigger distortion in the air path and required much more involved port "plumbing".

Does anyone know of any rotary "short stroke" valves? These would have the tubing ovalized axially along the center of the rotary valve, the idea being to make the valve rotor smaller and lighter.

Chuck has provided me photos relevant to his above posting:

http://photos.groups.yahoo.com/group/yo ... oke+valves

As an aside some photos of a Holton short stroke sousaphone:

http://photos.groups.yahoo.com/group/yo ... saphone+3P

Klaus

Your avatar suggests the suspicion, that you swallowed the 20K.

"Your not so kind interpreter"

Has anyone attempted over-square[1] valves on a tuba?

I saw a trumpet with them, but given the bore of even a small bore horn, I'm not sure it's be doable. Maybe utilizing mechanical advantage in some levers?

[1] over-square = larger bore than stroke, or valve is larger in diameter than the distance it moves. Very common in car engine pistons. See http://www.deniswedgwood.com/ovoids.html for some info.

ThomasDodd wrote:Has anyone attempted over-square[1] valves on a tuba?

Not to the best of my knowledge. But then, there are different design considerations to tuba valve design.

1) The "bumps" don't matter as much because their profile takes up a lower proportion of the valve port area than they do on trumpet valves.

2) Keeping valves light and small is what it's all about on tubas, which is why the short-strokers are unpopular with many--the valves have a shorter stroke, but are haavy and large.

Actually, if you didn't care about the cross-sectional size of a valve casing, a Berliner Pumpen valve has no "bumps" in it.

Chuck,
In the late 1800's horns were made with Allen valves, which were a rotary version of ovalized valves. I have seen these on Hall & Quinby, and Allen & Hall over the shoulder tubas, as well as a Lehnert centennial model tuba.
On the tubas I have played, they were far more ovalized than on the piston ovalized valve structures. While visually this gives the impression that they would induce resistance and stuffiness to the horns, all three such horns I have played have been exceptionally nice blowing horns.
It gives a very small diameter valve, perhaps a 5/8" diameter rotor for a fairly small bore over the shoulder E-flat tuba.
I'm pretty certain these are the subject of an early U.S. patent. When I locate it, I'll post a scan.

I played a Conn 4v offset recording bell all the way through High School (64-68). It was a great horn for that use at that time. I do not think that I could stand to play on today. It had a great middle register but no real bottom and the Bb above the staff was hard to hit.

Rob W. <><

Mikelynch wrote: I'm pretty certain these are the subject of an early U.S. patent. When I locate it, I'll post a scan.

Mike, I'd love to see that. The ovalized-port rotary valve seems to make a tremendous amount of sense for tubas, yet I've never seen one with it. Perhaps our German friends are just too conservative...

Mikelynch wrote:Chuck, I'm pretty certain these are the subject of an early U.S. patent. When I locate it, I'll post a scan.

I was looking for it and found this one, which is interesting. Using a piston like actutor for the rotors. I wonder if the linkage has problems.

I am impressed by your ability to create imbedded link. The next step would be to make them work.

Klaus

Oops. Sorry Klaus.

I changed it. Tried to take a shorcut and it didn't work.

Note, most systems need a plugin to view TIFF images. QuickTime works.

I've got a few plugs: ins and outs alike. Anyway the link worked now.

Funny to see this as a US patent. I have two of these instruments, however out of the GDR tradition, myself. Their valves are very fast:

A Scherzer Bb trumpet built exclusively in thin gold brass with a nickel silver wreath and nickel silver applications.

A Hoyer straight single Bb horn with a normal thumb activated 4th valve. A such instrument would not surprise US band musicians as at least King and l have made marching French horns of this type.

But the GDR straight Bb French horn is not inscribed in a marching context. It is a dual purpose instrument: dance band and modern orchestral music.

From my gallery index:

Thumbnails of a Hoyer trumpet shaped 4 rotary right hand valves (3 with quasi-piston action) single Bb horn for orchestral purposes. The 4th (thumb) valve lowers the instrument a perfect fourth:

http://photos.groups.yahoo.com/group/yo ... +action+BF

Klaus

imperialbari wrote:Funny to see this as a US patent. I have two of these instruments, however out of the GDR tradition, myself. Their valves are very fast:

This patent dates from a time where not every country had reciprocal recognition for another's patents. If you'll notice, the inventor is from Bohemia.

It seems like this patent is for two things--the first is a rotary-valved instrument with the tuning slides oriented upwards to avoid water accumulating in the tuning slides.

The second is the actuation mechanism and the housings for the valve stop arms and bumpers.

It's funny that it's dated 1936; piston valves on trumpets in the US had long displaced rotaries by that time.

Chuck(G) wrote:It's funny that it's dated 1936; piston valves on trumpets in the US had long displaced rotaries by that time.

That may be part of the reasoning for the actuators. It looks similar, and would be held/operated like a piston valved horn.

If only searches on pre-1976 patents were easier, there are a source for wonderfull reading. Even find the ocasionaly useful invention there, like Thayer's patents.