Peter Coggins mentions his converted "half" Duo-Art.  I don't understand
the improvement.  If the rolls are to be properly interpreted, as
opposed to merely pedaling up enough vacuum to cover any coding that
might occur, then attention needs to be paid to the demand of the roll.
In the modified system, without a spill valve, the feet need to serve
the function of a spill valve or the regulators will not provide the
correct vacuum level called for by the coding.  This doesn't seem to
be any less demanding of a job than just doing it the intended way.

If you want a full Duo-Art, I'm sorry but, you have to have a spill
valve.  It is part of the regulator system.  If you want to have a
combination machine, with both pedal and electric options, you will
have to add a spill valve.  The easiest way would be to make one, as
used on  the late model (fan regulator) Duo-Arts.  This is basically
an Ampico amplifier valve whose control line is connected to the suction
of both regulators through a couple of flap valves.  The higher suction
loads the amplifier valve.

At the risk of being shunned for non-original modifications I will
mention that my Duo-Art upright has such a spill valve.  It works
very well and is almost silent.  I located the pump remotely and with
that noise gone, the spill valve noise was objectionable.  The uprights
do not have the same muffler felt that the grands have.  This piano
plays better than any Duo-Art I have heard.  The spill valve was not
easy to regulate and had to be matched carefully to the pump speed,
which can be controlled by a variable speed motor.  The piano can play
evenly at 4" of water and can knock you over when the "crash valve"
comes on.  The original parts are all there for anyone who cares.
The original spill valve is held closed.

Has anyone seen another upright Duo-Art, like mine, that has a "crash"
valve.  It is a pallet valve that opens both theme primaries when level
15 on the theme side is reached.  This allows a little more air flow
through the theme ports for greater power.

Spencer Chase

 [ Peter's improvement is in the musical performance, which he is
 [ creating by establishing the Theme level himself.  His system is
 [ not an improvement of the technology.  I think he has trained
 [ himself to emulate the action of the spill valve, however, and
 [ so his foot-pumped performance should match that of a "full"
 [ Duo-Art system quite well.  Perhaps he might provide a sample
 [ on cassette tape.  ;)  -- Robbie