[ David Dewey wrote in 191220 MMDigest:

>  I can't seem to get it to put out more than 18" water gauge vacuum. 

For many years this volume control system on these plastic valve block
pianolas was a mystery for me.  However, I figured it out years back.

The four valves do not function as valves to operate anything -- they
serve only as a bypass.  It is important that the hole in the top of
the 4 valves be sealed closed.  Originally they had a sticky-back gold
piece of self adhesive paper.  These have usually fallen off so they
stay wide open, leaking lots of air into the system.  Make sure you
tape them closed or glue motor cloth over the holes.

The long forked piece that attaches to the reservoir is designed to
move a rod in and out of the pot metal box.  This spring loaded rod
moves a slide valve to regulate suction going to the suction motor
from the bellows system.

Two of the valve blocks are tee'd together and the other two are also
tee'd together.  Each pair attaches to a separate, long hose (tracker
bar size) that both go up to the "Soft", "Medium" and "Loud" knob in
the spoolbox.

With the knob on the low pressure "Soft" setting all 4 valve blocks
are in the off position.  With the knob moved to the center "Medium"
position two tee'd valves activate to on.  This opens a direct channel
through the valve blocks from the suction motor bypassing the slider
valve and giving more suction to the bellows.  Moving the knob to high
or "Loud" setting opens the other pair of valve blocks so that the
slider valve is totally bypassed and you get full suction to the
bellows system.

Once you have closed the top holes in the valve blocks (the knob is
on "Soft" and the unit is operating on lowest pressure softest volume),
you may need to loosen the screw on the set screw collar at the push
rod at the forked piece to the reservoir.  Moving that set screw collar
will regulate the "zero level" or the lowest level that the piano will
use. Set this so that all the notes play softly and the player is not
dropping out any notes.

This may be a problem since the original sponge neoprene valves
started leaking a few years into original use and the system takes
more pressure to operate.  Also, the valve travel is way wider than
the .035" travel needed for normal operation.  I have seen from .080"
to .150" valve travel which allows lots more air into the system and
requires higher pressures to operate.  Rebuilding the plastic valve
blocks with leather and setting them to .035" will make for a very fine,
soft playing pianola which few people have ever seen or heard.

Doug L. Bullock
Alton, Illinois
http://www.thepianoworld.com/