Christine Robinson's nice upright Gruenert Solophonola sounds exactly
like the Hupfeld mentioned by Roger Waring in 050923 MMDigest.  I'll
try to examine it and confirm details.  Making a tubing diagram will
take a while -- Hupfelds are never simple!  Meanwhile I offer the
following comments.

The aluminium unit valves are easy to service and very efficient
providing all the little leather valve washers and the mounting gasket
are in good condition.  The pouch envelopes are a kind of zephyr skin,
and can be rejuvenated and made airtight again if necessary with
Hydrophane.  This is important, or the bleeds effectively become much
too large and repetition suffers.

There is usually a spoolbox lever with four positions, three of which
control the Solodant and the sustaining pedal by mechanically suppressing
or releasing the primary valves, as Roger describes.

The fourth position is marked Expression, and enables a curious mode of
playing which purist pianolists don't like.  This allows the soft pedal
to be on (raises the half-blow rail) until you pedal just harder than
pianissimo, when the little pneumatic Roger mentions closes against its
adjustable spring, and turns the soft pedal off.

I have never been aware before of this pneumatic being connected with
the wind motor governor.  On Hupfelds, Silent, Forward and Reroll are
successively obtained by moving the tempo lever to the right beyond
maximum speed, and on earlier Solophonolas no accelerating valve was
fitted.  I think this valve on Roger's piano is a normal fast-bypass
valve which should be connected to the under-keybed pallet, but it may
be that it is intended to modify also the tempo expressively during
soft pedalling.  Some investigation is needed...

Patrick Handscombe
Wivenhoe, Essex, UK