As you say, it's only one of the factors in contributing to "piston speed." I think there are at least the following as well:
- Piston diameter (more area, more drag, Other Things Being Equal)
- Piston length (more length, more drag -- OTBE)
- Bore diameter (larger bore, less drag? -- OTBE)
- Overall weight of the piston+stem+pads/shims+??? assembly
- Spring strength (OTBE)
- Guide size/weight/material (OTBE)
- Lubrication (OTBE)
- ???? other things I may not have thought of
And EACH of these is "other things being equal" -- which they certainly aren't. So this is at least a 7x7 matrix of things that affect piston speed. Yikes. I'd be reluctant to focus on any one of them as an optimization target since the aggregate of the others might overwhelm it.
Gary Merrill
Wessex EEb Bass tuba (DW 3XL or 2XL)
Mack Brass Compensating Euph (DE N106, Euph J, J9 euph)
Amati Oval Euph (DE 104, Euph J, J6 euph)
1924 Buescher 3-valve Eb tuba (with std US receiver), Kelly 25
Schiller American Heritage 7B clone bass trombone (DE LB K/K10/112/14 Lexan, Brass Ark MV50R)
1947 Olds "Standard" trombone (Olds #3)