Hi All, This following letter came in today and it got me thinking.
"John: Experienced something I have never seen before. On the Bush
and Lane, I started to run out of foot pressure. I thought my valves
were screwing up.
"Not so! 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.
"What I intend to do is put a limiter on the bottom of the reservoir
so that is not stretched all the time in the non-playing (relaxed) mode.
Thought I might save you the same trouble down the road. Those springs
are hell bent for strong."
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 bellow 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 more I think about it, the more I wonder if failing to limit the
opening of a spring-loaded bellow doesn't significantly reduce the life
expectancy of the cloth? I think it's fairly well established that
stretching flexible, air-tight substances causes them to, how shall I
say it, 'get hard' faster than if it isn't stretched. The one example
in my mind that illustrates my point is tubing. When it doesn't get
overly stretched around a flange or nipple, it seems to stay flexible
for more years.
I'll write a 'Fact or Fiction' type article to the MMD and query the
group. If it's true that limiting a spring-loaded bellow does prolong
the life span and help prevent 'stress-pores' from developing, I think
it would be an important piece of information to all rebuilders.
Comments? Experiences? I'd like to know!
John A. Tuttle