The Duo-Art crash valve, I believe, is necessary for achieving a
'ffff' quad-forte power level.  It has been hypothesized by some that
they were gimmicks.  I think all techs by now find that half of them
have been adjusted out of the air circuit all-together.  But that's
a different story.

The crash valve on the grand isn't a "gimmick."  It works, and very
well -- for awhile, that is.  Then, it gets out of adjustment and has
to be re-adjusted.  I suspect that this was one of the devices in the
expression system that all resident techs and tuners were to adjust on
a regular basis.  I find, however, that they can be made to work
reliably for much longer, if one small change and an adjustment is
made.  Otherwise, the felt bumper on the pallet wears off rapidly from
the sharp edges of the machine bolt bumping it, so it's long-term
effect on the music is measured in weeks of heavy playing.

The change I suggest is to substitute a rubber-headed (or nowadays
plastic-head) nail for the felt that disintegrates until it can no
longer be touched.  The second thing I do to them takes a "feel" or you
will ruin it.  I emphasize caution here.  The pallet spring is just too
strong to actuate reliably each time it is bumped.  So I stretch the
springs purposely to weaken them quite a bit.  They still have plenty
of tension to stay closed, but are easily opened with a precise nudge
from the accordions.

The rounded rubber-headed nail is ideal to allow the arcing of the
machine screw adjuster to touch only the center of the dome, so it
touches it in the same place each time, as long as the body of the
pallet cannot budge on the bracket it is screwed to.  When everything
is down snug and the pallet actuation pressure eased, the crash valve
works to perfection, every time, and for years and years without any
more diddling.

As an aside to the musicality of the crash valve, some power 15s don't
require it, and some power 15s do.  So my suggestion when resetting
your crash valve is this: No "instantaneous" 15th step needs it.  Only
the ones that remain on, anticipating a full crash.  So although you
may see quite often a full 15th step, even in popular music, the crash
is set too closely if it operates here (not always, but generally
speaking).  You can tell when the arrangers intended it to work.

Since the roll arrangers were quite aware of the accordion's time
requirements to get fully into position, this happens to be one of
their most important criteria.  They often applied expression
combinations that they knew would not have full time to seat, and by
so doing, they were able to make compensations on the rolls without
sacrificing any accordion steps to do it.

You will, for instance, watch the accordions in heavy classical stuff
and particularly #4 will never quite bottom out all the way before
they have put in a different combination or added to it for a solid
accordion set, and yet the effect is the same overall.  It is so
common, when you watch the accordions work, that I'm a bit surprised
that this hasn't been mentioned yet by anyone else.  Clever, those
Yanks!

Craig Brougher