Hi There , The valve in my pipes has started making a loud croaking noise . not the bellows valve , the blow pipe valve . just wondered if anybody new how to fix it . it croakes when my arm is going out, not in . I think it must be something to do with the bellows because the noise stops 
when I use my other spare set of bellows . Please help .
Sometimes when the âhingeâ on the valve flap isnât in the correct position, the flap doesnât properly close over the hole. The correct position is with the hinge on top (i.e. at 12 oâclock).
Maybe the leather flap hinge is a little stiff and acts as a spring and the valve works as a reed creating a sound (croak), so press down the leather hinge to weaken it or put some blutac on the lower part of the leather flap.
If your original bellows works, apart from the croaking noise, and doesnât leak appreciably, then compare the size of the blowpipe ID to your non-croaking bellows. I have found that differences in the ID of the connecting tube can alter the way the valve responds.
Yes, itâs a resonance phenomenon. Making the valve flap either stiffer or looser may solve the problem for a particular bellows. Thereâs no âcorrectâ or âincorrectâ here, just an inherent compatibility issue between particular valve/blowpipe/bellows combinations. Even changing to a shorter or longer blowpipe when fitting to a smaller or larger girth can affect this.
It seems not to have been such an issue for the old style (19th c.) leather bellows outlet tube - it seems that design was less prone to resonances being set up.