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MMD > Archives > July 2001 > 2001.07.07 > 18Prev  Next

Adjusting the Pneumatic Bellows Correctly
By John A. Tuttle

Hi All,  I can tell by Larry Mayo's posting yesterday that he doesn't
really understand what I said in my posting about the Baldwin 'Manualo'
action.  And while I believe that Bernt Damm and I said basically the
same exact thing with regards to adjusting the "lugs", I would like to
repeat some information that has been well-known by rebuilders for over
80 years.

There are a couple of basic premises that should always be observed
when dealing with a bellows that is used to activate any device.
They are like 'unwritten rules', but I'll write them out.

Rule One:

A bellows should never be adjusted such that it fully closes.
Why?  Because collapsing a bellows 100% will put a tight permanent
crease in the cloth.  This causes the bellows cloth to wear out much
faster.  (If you need an explanation, write to me; I'll be happy to
explain it in detail.)

Preventing the bellows from closing 100% can be accomplished in many
ways, but the easiest way is to put a piece of felt, 1/8" to 1/4"
thick, inside of the bellows at a point that is just behind the space
taken up by the inward folding cloth.

Rule Two:

When at rest, the bellows cloth should never be stretched open in
any way, shape or form.  Why?  Because stretching the cloth
deteriorates the layer of material that makes the cloth air-tight.
And just like anything that is constantly stressed, it won't last as
long.  To prevent a bellows from opening 100% (thus eliminating any
stretching), something must be put in place that is stronger than the
forces working to open the bellows.

In the case of regular pneumatics, there is normally a wooden surface
under the movable board to which a piece of bumper felt can be affixed.
(In some cases, the mechanism is designed such that it is impossible
for the bellows to open 100%.  Here I'm primarily referring to air
motors and tracking devices.)  The thickness of the felt used should
be such that the bellows never opens 100%.  Anything under 100% is

In the case of spring-loaded bellows, a 'limiter strap' can be installed
either internally or externally.  (Don't understand?  Write to me.)

Naturally, you shouldn't restrict the bellows (when at rest) so far that
it no longer has enough travel to do its intended job.

Summing everything up, a correctly adjusted bellows is one that is never
opened or closed 100%.  The "working region" between the two limits
(Rule One and Two) must be great enough that the bellows can do its
intended job with ease.  What describes that limit, or the working
area, is the overall span of the bellows, minus the upper and lower
restrictions combined.


John A. Tuttle

(Message sent Sat 7 Jul 2001, 16:24:18 GMT, from time zone GMT-0400.)

Key Words in Subject:  Adjusting, Bellows, Correctly, Pneumatic

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