Hi Everybody,  This is a question for those folk who are familiar with
the late Duo-Art "Butterfly" expression box.  A couple of years ago I
managed to obtain a "new" one to replace the rather poor example
currently in my piano.

I was not at all happy with the performance of the "old" box, which
used leaf springs instead of coil expression springs, and tapes instead
of chains, to connect the butterfly intensity pneumatics to the curtain
valves.  In addition, it had suffered more than a little in a previous
restoration.

When I took the bottom off the "new" expression box, exposing the
various vacuum channels and the theme secondary valves, I discovered an
internal valve between the theme secondaries that is not in the "old"
expression box.  Everything else is virtually identical.

This "extra" valve appears to open a channel between unregulated suc-
tion and the regulated theme compartment, and my guess is that it is
a crash valve.

So far, so good.  It would seem that my original example didn't have
a crash valve.  Not unusual.

What is a mystery to me is that the pillow pouch of this valve doesn't
seem to have a connection to anything, nor is there any structure on
the butterflies that would appear to be a trigger for a crash valve.
In other words, how is the pouch inflated since there is no apparent
connection ?  Is something hiding under it that I should know about ?

I'm interested in your thoughts on this since enabling the crash valve
(if that's indeed what it is) would, I think, make a significant
improvement to the piano.

The other side of the coin is, if I am strictly out to lunch on this
one, what is this device and how does it work ?

Comments, please.

Jim Heyworth,
Sechelt, B.C., Canada
james_heyworth@sunshine.net