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MMD > Archives > February 2006 > 2006.02.20 > 05Prev  Next

Testing Air Motor Leakage
By John A. Tuttle

Hi All,  Obviously, there is some confusion with regards to my previous
posting.  The subject of the posting was "Testing an Air Motor".
However, it was changed to "Satisfy the Customer with Minimal Repairs".
And, while I admit that the posting did go into some detail about
satisfying the customer as opposed to satisfying my own personal
desires, a point I was also trying to make about air motors seems to
have been missed.  So, I'll try again...

I hope we can all agree that sealing the vacuum port and turning the
crankshaft backwards is probably one of, if not, the best tests to find
out if the motor is in good shape.  And, I will go a step further in
that direction and say that the test will also reveal particular
weaknesses in the motor, such as a bad valve, a leaking bellow, etc.
However, and I cannot over-emphasize this fact, beyond a certain point,
the above test is worthless.  In cases of severe leakage, you simply
cannot turn the crankshaft fast enough to get a good sense of how badly
the motor is leaking.

Naturally, you could, as I often do, simply put your mouth on the
vacuum supply flange, hold the crankshaft tightly and suck hard (or
fast). But, that too can still be a little misleading because your
lungs only hold about a quart or so of air. The exhauster bellows
exhaust about twice that amount with each pump.

Mind you, my initial posting on this topic was about the effect that
severely leaking air motors have on the overall performance of a player
system, and the fact that even though the motor may appear to be in
relatively good condition and 'functioning', it could indeed be the
exact cause of the problem the customer is complaining about, i.e.,
having to pump too hard or fast to enjoy the music.

John A Tuttle
Brick, New Jersey, USA

 [ The "Subject" of MMD articles is chosen by me to be consistent
 [ with the discussion thread; it generally reflects what the majority
 [ of the article is about and so it may be a bit a different from
 [ the author's suggested Subject line.  Sometimes I split rambling
 [ messages into separate MMD articles.  (John's articles are always
 [ well-focused, however.  ;-)  -- Robbie

(Message sent Mon 20 Feb 2006, 15:00:31 GMT, from time zone GMT-0500.)

Key Words in Subject:  Air, Leakage, Motor, Testing

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