I not only examine bellows cloth before use, I have been noting several
already rebuilt pianos that are no longer airtight.  Usually after only
10-15 years.  These, of course have PPC bellows cloth and motor cloth.

There is a test that I perform on some bellows to demonstrate the
problem to the customer.  If there are no visible holes in the cloth,
I take out a large pneumatic like a sustaining pedal pneumatic and make
some soapy water and with a rag, wipe a large area of the cloth with
the water.  I then blow into the pneumatic and the foam exuding from
the cloth is a very effective demonstration of why the piano will not
play.  I and the client then surmise that the whole piano has this
cloth throughout it and indeed it does.

D.L. Bullock    St. Louis
www.thepianoworld.com