Re: Re: Re: Re: Re: Re: Re: Vienna Valves on the Tuba


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Posted by Wade on August 27, 2003 at 17:11:12:

In Reply to: Re: Re: Re: Re: Re: Re: Vienna Valves on the Tuba posted by 10:30 afterthought on August 26, 2003 at 14:17:25:

Rotary valves, large, small, traditional, or non-squished (Rotax) all make a 90º bend in the tube routing, whether or not the valve has been activated.

Observe that the rotor casing is essentially a very short tube with four holes in it's side. The holes are at the NE, SE, SW, and NW corners of the side of this tube. These four holes are each 90º of angle away from one another.

The tubes connecting valves to one another are called "knuckles".

On piston valves, these are "permanently" joined to the casings by silver solder, making the piston set, in effect, one single piece.

On a rotary instrument, each valve has four knuckles that can be pointed wherever (within reason) the manufacturer chooses to send the air. Generally, this is either directly from or to an adjoining rotor, or to a slide loop. By stacking rotors one on top of the other, this requires that the knuckles bend at 45º angles to either point straight up or down. Also, the remaining two ports need the knuckles (usually) to point parallel to one another, requiring them to have 45º bends as well. This gives the viewer the impression that air enters the open rotor and goes straight through to the exit port.

What actually happens is that the air enters an open rotor (usually) via a 45º turn, goes through a 90º turn in the other direction, and exits via another 45º turn. If it is going on to another rotor, then the routing is actually in via 45º, through at 90º, out and into the next via a 90º turn, through via a 90º turn, et cetera.

To go through a slide loop, let us imagine a two rotor instrument with 1st pressed and 2nd up. Air goes into the 1st valve and continues through it via a 135º turn and exits via a 45º knuckle into the slide tube. When it returns to the rotor, it enters at a 45º angle, and proceeds through, out, and into the next rotor via a 180º turn, where it is then shunted either into the next slide or on to the next rotor.

In my experience, there is only one commonly used valve that has a totally straight airway when not activated. And that is the Thayer Valve so common on modern trombones. (Note that I said "commonly" as I am aware of a few other valve designs that have this characteristic, but are not in use in enough numbers to refer to them as being common.)

Wade "clear as mud" Rackley


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