John A. Tuttle wrote:

> The left reservoir had pin holes in it.  What had happened was that
> the springs in the reservoir are so strong that they actually pulled
> the cloth so much that the cloth developed pin holes in it.  Have
> never seen this before."

This is not caused by the springs.  It is caused by the crap sold by
Durrell Armstrong in the late 1980's and early '90's.  We found the
problem in the brown Aeolian pump cloth when we covered a pump and
hooked it up on the table to test the Duo-Art system with.

When first cranked up it pulled 120" water lift.  After a week of
running several hours a day it was only capable of 20" and we began
examining the leather flap valves.  After replacing those a couple of
times, with no improvement and at our wits end, we took the cloth off
and found that when held up to the light it looked like a farmers
plowed field.

This was taken up with Durrell, of Player Piano Co., who had supplied
us with the cloth, and he said he knew this was a problem.  We asked
him why he had not withdrawn it and told us he said he had thousands
of feet of it.  We tested it by dissolving the cloth in chemicals and
looking at the rubber layer.  Durrell said it should have two layers
and it did not.   He said that the cloth was polyester and it stretched
too much as well. He had another run of the cloth made in about 1992
and sent us our 20 yards free.  This upset me greatly knowing that
I now had customers out there with time bombs in their bellows.
I found the same problem in the heavy and light black cloth ten years
after I put it in my piano.  I have since never trusted anything from
PPCo.

There is no amount of strapping you can do to prevent this.  It will
happen and it is the air pressure that will do it.  Just make sure your
bellows cloth is cotton canvas and natural gum rubber inside.  I am now
restoring a Duo-Art pump and its cloth is soft and flexible with no
holes in it after 70 years.  It was built in 1930.  That is what
natural gum rubber does.  The synthetic rubber Durrell used to use had
a very short life and probably most of that life was spent on the
shelves at Player Piano Co.

> I replied:  Thanks for sharing the tip.  I recall seeing a limiter
> strap on the reservoir bellows in some reproducing pianos.  Can't
> remember which ones for sure, but I remember thinking they were
> there to limit the movement of the bellows so it would work within
> a limited amount of space.  The idea that they (the straps) may have
> also served to prevent the material from stretching and thereby
> reducing its air-tightness never crossed my mind."

The limiting straps are found in reservoirs mainly to allow you to
install the springs and easily cover the bellows.  They served the dual
purpose in the PPCo polyester and synthetic rubber cloths of keeping
the opening correct and without stretching the cloth, but there were no
originals that had that problem that I have ever seen.  I had cat fits
with stretching cloth back when Durrell was supplying that bad cloth
throughout the 1970's and 80's

Originally the strong springs would have stretched the reservoir
about 1/8" or less, but that was planned for and it was not a problem
for gum rubber in the cloth.  As far as I can see the only thing that
deteriorates gum rubber is sunlight.

The answer to this problem is simply to recover every bellows system
that was covered more than about 5-7 years ago using the newer
Australian gum rubber cloths.

D. L. Bullock    Piano World    St. Louis