Posted by Chuck(G) on April 25, 2002 at 13:47:00:
In Reply to: Re: Piston or Rotary posted by John S. on April 25, 2002 at 09:08:53:
I'll quibble with one of your statements:
Rotary valves have less mass than piston valves.
All piston valves are hollow; most rotaries are solid. For any given tuba bore size, take a valve piston and the corresponding rotor and its connecting hardware and the rotary version will usually be considerably heavier. I one owned an 0.900" bore BBb with rotors that must've weighed somewhere around a half pound apiece, not counting the linkage. Made my fingers ache to play it.
Rotary valved tubas tend to place the valve cluster farther from the mouthpiece than their piston cousins. This usually means that a larger bore through the valves is involved. A 6/4 CC in piston usually has somewhere around a bore of 0.750"; the corresponding rotary bore is about 0.840", meaning bigger valves.
One of the problems with rotary valves is that the rotor doesn't contact the casing walls. This means that there is inevitably going to be a certain amount of leakage. A well-fitted piston tends to leak less.
Pistons seem to have a wider variety in the way they can be configured; a rotary is pretty much limited to either routing the air straight-through or turning it through two sharp right angles (not good acoustically).
FWIW, I own both piston and rotary instruments, but like the feel and response of the piston varieties better.