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MMD > Archives > January 2005 > 2005.01.26 > 09Prev  Next

Sealing Bellows Leaks with Pliobond
By Craig Smith

Conrad Bladey asked about Sealing Bellows Leaks in an organette.  This
is always a compromise.  Done properly, it is always best to replace
the bellows cloth with like material.  Everything is now new and it
gives you the chance to replace the valves at the same time.

On the other hand, if the valves are okay (or you can access them
otherwise), it is tempting to just refurbish the pneumatic cloth
without the bother and expense of replacing it.  Small tears can be
repaired with thin cloth or leather.

If the cloth is otherwise sound (doesn't tear easily), this is probably
a good approach.  But if the cloth has lost its rubber coating so that
you can see the threads in the bare spots, you might be able to rescue
it with a new coating.  Player Piano Company (PPCo) used to sell a
liquid Neoprene that you could paint onto the cloth to restore it.
I think that product is no longer available.  I used it years ago with
some success but, if I recall correctly, it didn't last.

When I find myself in this position, I try using Pliobond.  It is a
'liquid rubber' in a bottle or can.  You can use it like contact cement
or as a glue.  But if you thin it out with acetone it makes a great
sealer.  Just paint on a thin coat with a soft brush and let it dry.

Do not move the cloth while it dries.  Let it dry with the cloth as
flat as possible.  If you move it too soon, the cloth will stick
together, so wait a day or two.  You can also dust it with talcum
powder for extra protection.

I restored a Wurlitzer harp a few years ago.  It had 60+ bellows and
they were all crispy and leaking.  The 1" by 3" bellows were leaking
up to 100+ cubic inches per minute.  In many places you could see right
through the cloth.

After some experimentation, I applied Pliobond to the cloth and reduced
the leaks to less than 5 cubic inches per minute.  The surprising
benefit was that the cloth felt almost like new -- not crispy at all.

I had a devil of a time sealing the pump.  I measured the leaks and it
was near the top of the range, which is 12000 cipm.  In the end, I got
it down to less than 500 cipm leakage.  But the leaks were not in the
cloth.  It leaked that much through the wood and the edges of the screw

Pliobond is much better than rubber cement, which peals off easily and
deteriorates with age -- I did some objective testing to verify that.
Pliobond contains ultra-violet light inhibitors and other chemicals to
address these problems.

By the way, Pliobond is flammable and contains rather strong solvents.
Use it with adequate ventilation.

Craig Smith, Upstate New York - Geez, it's snowing again, Ron!

(Message sent Wed 26 Jan 2005, 14:40:15 GMT, from time zone GMT-0500.)

Key Words in Subject:  Bellows, Leaks, Pliobond, Sealing

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