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MMD > Archives > December 2001 > 2001.12.17 > 12Prev  Next


Low Suction Air Motor & Other Possible Problems
By Craig Brougher

I'm curious, Tim.  Don't take this wrong, as I am not challenging
you as to the type of air motor you need, of course.  You say it's
a "small-tubed" air motor.

There's one thing I do not intend to imply, and that is, "I've seen
them all.  I know it all, and I'm goin' tell you whut."

Every time I think I've seen every Pratt Reed (or anything else) that's
ever been born, then I see another.  So maybe you could give us a
dimension or something.  Now let me tell you what I have seen.

The "ultimate" smallest regular-design air motor I have personally seen
is in the Art Echo Reproducer drawer.  The block measures 5-1/4" wide
and 4" high.  There are 4 tiny bellows attached, and 2 sliders.  The
tempo throttle is attached to its bottom and that adds about 1-1/4" to
the height.

Now you'd think that a tiny air motor like that would require higher
pressure to do the same amount of work, and you'd be correct.  Except,
they do it differently.  They run it at twice the speed and gear it
down.

My point is this:  It uses the same pressure (vacuum) that any motor
uses.  So does the Gulbransen cylinder motor and the Gully 3-point
motor.  The reason is because all early pneumatic player pianos use the
same pump pressure range.  Their regulators may be vastly different
(the Art-Echo motor regulator is very small, too), but the pressure to
the motor is the same and overall, the volume of air they all require
to do the same amount of work is still the same.  Just because an air
motor is tiny and has small tubes doesn't mean it runs on a higher
pressure.  It cannot run on a higher order of pressure than the piano
unless some very fancy steps are taken to do that.

The Pratt Reed, Standard, Aeolian, and Simplex air motors were all
designed to play in the same pressure range as the Art-Echo.  So that
now brings me to the next point: If the replacement air motor you now
have is running the roll just fine, and the regulator and air motor
isn't leaking or losing power somehow, then the problem with hard
pumping isn't the fault of the air motor.  You will not gain anything
by substituting air motors.  You have another problem.

I would suggest that you first isolate the trouble by having someone
wind the take-up spool by hand as you pump the notes to play.  The air
motor will take up to 25% of the air in a player, so factor that in
first.  Play through at least two rolls, manually propelling them and
treadle them through by foot, and you will get a feel as to whether it
is the air motor circuit or not (which can still be leaking through the
governor).  If so, then I suggest that you have a leak in the air motor
circuit, or a sticky transmission that requires too much power to turn.

The original old Pratt Reed air motor was integral with its governor.
It was a tough unit to get regulated sometimes.  If someone has replaced
both the original governor and motor with something else, then if they
have taken care of the control rod linkage at the same time, believe
me, you don't need to return it back to original.  It will work that
way.  All you have to do is take care of your leaks, which may not be
the air motor at all, but (my suspicion is) the stack valves.

Craig Brougher


(Message sent Tue 18 Dec 2001, 01:34:10 GMT, from time zone GMT-0800.)

Key Words in Subject:  Air, Low, Motor, Other, Possible, Problems, Suction

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