I made a few typos in that last attempt that I want to correct just
for the record.
First of all, it is not possible for a valve with a fixed, normal-sized
bleed to reliably actuate from a trackerbar at 3.5", much less 2.5".
And were a Duo-Art valve (of all possible selections) to operate
reliably at 2.5", then it would have to be tested reliably first at
2". No original valve with a fixed bleed, even a #70 bleed, will even
budge. So we can totally discount these figures, and from now on
address the real world.
Duo-Art zero intensities vary of course, but 5" is a mean average
around the room. At 5" of pressure -- on which, by the way, many very
good Duo-Arts will still not quite play all of their notes reliably --
each pneumatic is able to provide .465 theoretical pounds force on the
striker. That's 211 grams. Not a lot, but will overcome probably 80%
of the jack letoffs in the real grand world.
You see, Julian and Paddy, it is possible to calculate these things.
However, there again, this figure is ideal and doesn't take into
consideration some very honest deviations, losses, and point of contact
errors that cannot all be factored in, but which exist in wood, cloth,
and leather contraptions.