Posted by Todd on November 10, 2000 at 12:53:02:
In Reply to: Piston vs. Rotary Valves Info. Request posted by Phil A on November 10, 2000 at 12:24:20:
Hi,
Let me first start by saying both of my tubas have a 4+1 configuration...meaning 4 pistons+1 thumb rotar.
I am currently taking a class in brass repair at Ithaca College. We recently discussed the pros and cons of maintaining and working with both pistons and rotars. Pistons have a nice fluent direct valve stroke that has no "middle man" such as rotar linkage. With that said, rotars(for the most part) have a shorter "valve stroke" since the rotar has to turn very little (1/4 turn) in comparison to the length the piston needs to travel. There are SOME exceptions including the big Conn BBb relics with short valve strokes.
Pistons have far less parts than rotars which makes them prefered in the scope of self-maintance. Though, as I have learned, rotars aren't scary or a voodoo that some people make them out to be. With simple instruction, a decently handy(not all thumbs) individual should have no problem disassembling a rotary valve and the linkage to clean, lubricate, and adjust the valve.
Rotary valve tubas come in larger bore sizes than piston valve tubas. Why? I am not EXACTLY sure, but it was explained to me as such. Rotary valves can be drilled larger (the bore of the valve) and still maintain a reasonable valve stroke. With pistons, the valve stroke would increase a significant amount due to the larger hole drilled in the piston. I was also told that the structure of the piston does not promote larger bore sizes because it would sacrifice the integrity of the valve making it weak or some such. I am not sure this is true, but that was one of the tales I heard along the way.
One of the cons of rotary valves is all of the linkage. There are is a lot more external mechanisms in using (pressing) a rotary valve than there is in pressing piston valve. These external mechanisms may fail to operate at some point, break, get bent, etc. Sure things can happen to the pistons and piston stems, but being that there is physically more material exposed in the rotary valve mechanism makes it more vulnerable to damage. The up side is....you can buy hobby shop parts to fix this linkages that work as fine as a full replacement of parts thru the original manufacturer.
So...you ask yourself....why does he seem to favor rotary valves BUT own a piston valve tuba? I love my horns! Nuff said! :) I would entertain owning a 3rd horn...possibly a 4/4 5 rotary valve tuba.