Theory behind switching rotary linkage to same direction

[Dean E]

I do not understand the theory or advantage to switching rotary linkages so that they all operate in the same direction.

Perhaps it has something to do with taking advantage of the supposed velocity of airflow.

How big a job is it to accomplish? Does it require fabricating new linkages or rotor stops?

I look forward to your comments.

Thanks.

[Chuck(G)]

The way I've seen it done is simply to drill a new set of stop plate holes on the other side of the casing and plug the old ones. I suppose one could also use the same set of holes by fabricating a new stop arm (with the pin on the other side of the linkage).

[windshieldbug]

Actually, I could see a point (not saying that I agree, however) if the rotors are smaller than a certain diameter compaired to the bore... if turning one way opens up both air passages at the same time, while the other way only opens to the valve tubing in question.

[Chuck(G)]

What's the point?

But that wasn't the question, which was "Howzit Dun?"

People do all sorts of strange things to otherwise fine instruments.

[Alex C]

The rotation of a rotary valve results in one of two situations. Either the airflow in the portion of the rotor entering the side is reversed when the valve is pressed or, when the rotation is reversed, the same thing occurs in the outgoing tube of rotor back into the tuba when the valve is pressed. In neither case is a reverse of airflow avoided in one of those inches of tubing internal to the rotor avoided. If you think it's an issue of great magnitude- sort of like lacquer vice plating- switch to pistons where the flow isn't reversed and just has to be started from a static state for that inch of tubing in the piston. Of course the several inches of static air in the slide itself is identical in either case. In no case is the propagation of the sound particularly connected with the direction of airflow at the velocities involved. I suppose those super sensitive embouchures of the tubenet cogniscenti as opposed to us mere hoi paloi can feel a severe impact on their lips from the flow pressure backing up down the leadpipe. Feel free in any case. Henry

Well done. You have a good explanation, well thought through, a valid conclusion and a good suggestion. Rare.

I even had to look up "hoi paloi."

Charley Krause had an interesting experience where someone was demonstrating rotaries; clear tubing was attached to a rotary valve section and the tubing was filled with smoke. When blowing air through the tubing the smoke momentarily backed up every time a valve was depressed. Charley can correct whatever small mistake I might have made here.

The only place I would differ in this thread is that the real issue is not the air flow but what is happening to the vibrating air colum when a rotary is depressed.

I did notice that, however, that Roger Bobo was able to overcome the problems associated with rotaries.

Conversely, Harvey Phillips was able to overcome piston valves. hmmmmm

[tubamirum]

The fallacy of comparing blowing smoke through a horn to sound waves is that they don't act the same and don't move at the same speed.