Posted by Chuck(G) on May 14, 2002 at 13:19:05:
In Reply to: Question: piston or rotary valves? posted by Michelangelo on May 13, 2002 at 17:13:46:
Even though this one keeps coming up regularly, I'll toss something in that I haven't seen mentioned heretofore.
When it comes to tubing layout, rotary valves are essentially 2-dimensional; that is, the entry and exit ports on a rotary valve must line in the same plane. This leads to the almost-identical layout for the shorter tuning slides seen on most rotary tubas--there just aren't a lot of alternative places for the tubing to go. And the flow is either straight-through or diverted through two right angles.
On the other hand, piston valves are more three-dimensional. The designer has a considerable amount of freedom when it comes to placement of ports. Witness the bewildering variety of layouts on piston-valved instruments. Of course, this same freedom can result in a truly execrable instrument, also.
As an example of this design freedom, on my B&H 983 Eb instrument, the tuning slide closest to the bell is NOT for the first valve, but rather the fourth! Boy howdy, that had me going for awhile...
I conjecture that this aspect of piston valves can result in a more free-blowing aspect than rotaries when valves are brought into play.
Rebuttals, of course, are welcome.