Does anyone own, or has seen, a Hupfeld with individually mounted
aluminium valves mounted on two decks of laminated wood and leather?
A tubing diagram would be extremely useful.

The valves are held in place by coil springs and sprung tongues,
and are great for servicing.  They seem pretty airtight too.  They
contain the little paper envelopes and lifter cards.  I do not have
any problems with these.

My real problem is understanding the function of the expression box
mounted to the left of the upper action.  Although the three main
inlets and valves are obviously associated with the Solodant
expression settings, I am confused by a small pneumatic that closes to
cut off air from a valve in the wind motor governor, which is mounted
on the right of the upper action.  If it does not close fully then air
is allowed in to the connecting tube and the wind motor runs fast, as
if in reroll mode.  I should stress here that the normal control for
reroll mode is fine.

When the expression settings are in the off position, the control lever
shuts off air supply to all three valves and forces down the small
pneumatic via a small spring.  When in the on position, the small
pneumatic is only partially closed, and becomes fully closed only as
a result of energetic pedalling at the start of a roll.

Now I could, of course, put a thicker leather cover on the shutoff
plate so that less pressure is needed, but why should it be necessary
to control the wind motor in such a manner?  Or have I got the tubing
totally wrong?

All help appreciated.
Roger Waring - The Pianola Workshop
Solihull, West Midlands, UK
http://www.pianola.co.uk/