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Understanding Vacuum and Pressure
As they relate to Player Pianos

Like compressed air, vacuum puts the atmosphere to work. But unlike compressed air, vacuum uses the surrounding atmosphere to create the work force.

Evacuating air from a closed volume develops a pressure differential between the volume and the surrounding atmosphere. If this closed volume is bound by the surface of a vacuum cup and a workpiece, atmospheric pressure will press the two objects together. The amount of holding force depends on the surface area shared by the two objects and the vacuum level.

One inch of water equals 0.036127 psi

Hi John, since we use inches of water column , 1 pound pressure will raise a column of water 27.6799048425 inches.

The table Jody suggested did not seem to answer your question. Here are the conversion factors in both directions: Pressure in psi X 27.6778 = Pressure in Inches of water Pressure in Inches of water X .03613 = Pressure in psi

Typical vacuum cleaner reduces air pressure by about 20%

In 1654, 1. Otto von Guericke invented the first vacuum pump[36] and conducted his famous Magdeburg hemispheres experiment, showing that teams of horses could not separate two hemispheres from which the air had been partially evacuated. Robert Boyle improved Guericke's design and with the help of Robert Hooke further developed vacuum pump technology. Thereafter, research into the partial vacuum lapsed until 1850 when August Toepler invented the Toepler Pump and Heinrich Geissler invented the mercury displacement pump in 1855, achieving a partial vacuum of about 10 Pa (0.1 Torr). A number of electrical properties become observable at this vacuum level, which renewed interest in further research.

How many inch mercury in 1 inches water? The answer is 0.0735559124637.
We assume you are converting between inch mercury [0 °C] and inch water [4 °C].
You can view more details on each measurement unit:
1. inch mercury or inches water
The SI derived unit for pressure is the pascal.
1 pascal is equal to 0.000295299830714 inch mercury, or 0.00401463078662 inches water.
Note that rounding errors may occur, so always check the results.
Use this page to learn how to convert between inches mercury and inches water.


Hi John, since we use inches of water column , 1 pound pressure will raise a column of water 27 inches.

From: rumpf.paul@yahoo.com.geentroep (Paul Rumpf)
To: rolls-1201@mmdigest.com
Date: Fri, 24 May 2013 04:00:29 -0700 (PDT)

Subject: Player Piano Valve Design Parameters

John Tuttle asks some questions in 130520 MMDigest for which there are
simple answers and complex answers.

Taking the questions in turn:

> > 1. Does the square area of the pouch have to be bigger than the
> > square area of the valve seat?
The simple answer is "yes".  The reason for this is that the pouch at
rest has to lift the weight of the valve stem plus the weight of the
vacuum force which forces the valve to shut tightly. Five inches of
water gauge is a pressure of 0.185 psi. Consider the pouch as a piston
and its lifting force is, for a one inch diameter pouch,

  Force = pi/4 x 1 x1 x 0.185 = 0.145 lb.f = 2.35 ounce force

The weight of a 'Standard' valve stem, etc., is about 6 grams or 0.2
ounce.  The valve disc diameter is about 0.67 inch.  The downward force
due to the valve disc is:

  = pi/4 x 0.67 x 0.67 x 0.185 = 0.065 lb.f  = 1.04 ounce force.

So the opening force is 2.35 ounce and the force plus mass of the valve
is 1.04 plus 0.2 ounce force; = 1.24 ounce force.

If the valve disc was the same diameter as the pouch, then the pouch
could not lift the valve.

> > 2. In terms of physical size, is there a finite point at which
> > a pouch and valve are so big that the pressure of the atmosphere
> > is not great enough to activate the valve?
The simple answer is the atmospheric pressure has nothing to do
with the lifting of the valve.  The valve lifts because of the pressure
difference between each side of the pouch. See below: 3 and 4 

> > 3. What is the exact ratio between the size of the bleed and the size
> > of the hole in the trackerbar at which the note will fail to activate
> > when the trackerbar hole is open to the atmosphere?
The simple answer is "there is no simple answer."  The tracker bar is
connected to the pouch through a long tube.  Outside the tracker bar is
atmospheric pressure.  When the tracker bar is open, air flows through
the port and the tube through the bleed to the vacuum supply.  There is
a pressure gradient along this tube, but ideally this pressure gradient
is small, so that under the pouch, the air pressure is close to
atmospheric pressure.

It is the flow of air through the bleed, which gives rise to an air
flow which increases the pressure gradient along the tube.  This
results in the air pressure under the pouch falling from atmospheric
pressure, to a pressure closer to the vacuum level above the pouch.
This reduction in pressure difference across the pouch reduces the
force development potential of the pouch. From this point of view a
small bleed is to be preferred.

> > 4. What is the exact ratio between the size of the bleed and the
> > size of the hole in the trackerbar at which the note will fail to
> > turn 'off' as fast as it turns 'on'?
The simple answer is "there is no simple answer."  The bleed must
remove the atmospheric air under the pouch when the tracker hole is
covered again, before the valve can shut off.  For reasons of closing
speed, the bleed should be large to extract the air more quickly,
but in question 3 we showed the bleed should be small.  So the bleed
size is a compromise.  The obvious example of bleed sizes, is the
Ampico model "B" where there is a small bleed for turning the valve
on and holding it on, and a larger bleed for exhausting the pouch when
the valve turns off.

> > 5. Are there formulas that a person without a degree in physics can
> > understand that can be used to accurately determine things like the
> > optimum size of a pouch, valve, a bleed, and striker pneumatic?  Or
> > was it all done by trial-and-error?
The simple answer is that most things can be understood through quite
simple explanations but design matters involve more rigour.  Bleed
design is a compromise and is affected particularly by pouch material
selection and its leakage stability over time.  In my paper about force
development (in the MMD Archives) I consider such matters as force
development in pneumatic motors.  Such work generally comes along after
the initial experimentation has confirmed an approach, but quantifying
an engineering systems through mathematical models is invariably
necessary for product optimisation.  See


I guess there was some guess work, but the anecdotal evidence relating
to the story of Dr. Hickman's arrival at the American Piano Company,
shows how mathematical modelling is an important part of all product
design and manufacturing.

Paul Rumpf

Although I prefer that you send E-Mail, if you have a non-order related question, you can reach me at 732-840-8787. If I'm in the Shop or at Home, I will answer the phone. Otherwise, please leave a message.

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