Regulating vacuum without electronic overkill
 [ Ref.: Vacuum Transducer for Motor Speed Control

Greetings,  There is no reason to introduce electronics in order to
regulate vacuum.  Player pianos have been doing just fine for many
years without electronics.

Just put in a pneumatic regulator with a spring and adjustment lever,
or make what I think is the best regulator ever applied to players,
the diaphragm regulator.  I have one on my E-Roll player test setup
and it is small efficient reliable and was easy to build.  It is just
a diaphragm that closes off a perforated grate through which the vacuum
flows.  The pressure level is set by a fixed reference on the other
side of the diaphragm.

Mine is made of Delrin and machined on the mill.  It is about 5 inches
square by 2 inches, only because I designed it on the mill.  A careful
design would have made it smaller.  It could have been made out of
wood, just as easily.

I have the reference vacuum set by the relative leakage between a
supply and a bleed needle adjuster.  The good quality aquarium valves
will work but so will a carefully drilled bleed, once you get the
leakage right.

My tester has four switches that operate solenoid valves to open
each reference leak.  I can therefor get something like seven or eight
different levels from 4 to 100 inches, quickly and repeatedly.  A fine
thread adjustment needle of good quality would make a fine volume
control.  Don't forget to put a spring loaded spill valve on the pump
to make sure it gets some cooling air if it is an air cooled turbine.

Virtually all AC vacuum turbines are universal series wound motors and
it is very easy to control their speed with voltage control.  A Variac
or high power light dimmer (pwm triac control) or tool motor speed
control will work fine but the vacuum will vary if the demand exceeds
the supply.

If you want to control the speed of a box pump, the cheapest way is to
replace the AC motor with a DC motor and use a speed control.  I can
often find 110 volt DC motors for less than cheap AC induction motors
because there is less market for them.  I buy every one I find for less
than $20 and many for a lot more.

I can extend the life of a leaky pump for years by creeping the speed
up a little each year.  I kept an original Ampico pump running for five
years of heavy service on my Duo-Art which I play daily and for many
hours on occasion.  The pump is under the house so it was no big deal
that it got louder.  Not loud enough to keep the mice from moving in
unfortunately.

Best regards,
Spencer Chase
Laytonville, Calif.
http://www.spencerserolls.com/