How to improve airtightness?

[Johanna]

My otherwise lovely aeola is acting up, and it's so frustrating.

 

I had Bob Snope work on it earlier this year, and he sent it back in excellent shape.  But since then, I've had three pads come off, so I've had to open it up quite a bit, and now the airtightness just isn't there.  I didn't time the "bellows hang test" before, but now the bellows open almost fully in 15-20 seconds, which seems quite fast.  And the notes don't feel like they have quite the same "bite" as they used to on rhythmic fast tunes, and I'd very much like to get that back..

 

How do I troubleshoot this?  I assume that the bellows would not have sprung a leak in the past six months, so the air must be getting in either around the gasket or around the pads.  (I just glued the old pads back in place, but maybe they're not seating as tightly as before?)  I don't feel any particular leaks when allowing the bellows to close under the instrument's weight (doing the trick of holding it up to sensitive parts of my face to better feel any air flow).  I've tried fluffing up the gasket with a thumbnail/screwdriver, but it doesn't seem to have much effect.

 

There was what looked like a thin layer of residue on the gasket and on the action board where it contacts the gasket.  I don't know whether that's accumulated grime or some kind of sealant that a previous owner applied.  I used my fingernail to scrape most of it off, but maybe I should not have done that?

 

What would you do if you were me?

[David Barnert]

Squeeze it under water and see where the bubbles come out (only kidding ).

[David Barnert]

32 minutes ago, David Barnert said:

Squeeze it under water and see where the bubbles come out (only kidding ).

 

It occurs to me that I have used that line before in response to a similar question, so I did a search on the word “bubbles” and found that, in fact, I had (three times!).

 

Here are the threads, some reasonable suggestions to be found therein:

 

 

 

 

Edited October 11 by David Barnert
typo

[Tiposx]

It sounds like the gasket has given up and needs replacing.

Edited October 11 by Tiposx

[alex_holden]

If you have reglued pads it's possible one or more isn't aligned well. One thing to try is to take off the action box, remove the lid, then go into a darkened room and look closely at each pad from below while shining a bright light on it from above. Sometimes you can see a crack of light that indicates the pad isn't sealing correctly.

[RAc]

Another possibility is that one or more of the triangular wooden blocks that hold the reed plate in place has come loose.

[Greg Jowaisas]

4 hours ago, RAc said:

Another possibility is that one or more of the triangular wooden blocks that hold the reed plate in place has come loose.

A good point.  In which case often notes in a certain area of the reed pan can sound weaker than the rest.  Support blocks need to be secure and the proper height.  Do not overlook a potentially weak one, loose, but hanging on to the chamois seal.

[Johanna]

7 hours ago, David Barnert said:

Squeeze it under water and see where the bubbles come out (only kidding ).

 

I know you're kidding, but it occurs to me that hardware stores sell foaming leak-detector compounds for finding leaks in tires, gas lines, etc.  Would these be safe to use on the seam between the action box and the bellows frame, or is that a terrible ideal?

 

6 hours ago, Tiposx said:

It sounds like the gasket has given up and needs replacing.

 

That's what my instincts tell me too - the gasket has clearly been through a lot, although I feel I've seen gaskets in worse shape doing a better job of sealing (and this one was doing a much better job until a few months ago).  I recall being told, once upon a time, that replacing a gasket is not really a DIY job (and the Concertina Maintenance Manual doesn't even mention it).  Is that still the prevailing wisdom?

 

6 hours ago, alex_holden said:

If you have reglued pads it's possible one or more isn't aligned well. One thing to try is to take off the action box, remove the lid, then go into a darkened room and look closely at each pad from below while shining a bright light on it from above. Sometimes you can see a crack of light that indicates the pad isn't sealing correctly.

 

I did try this.  I'd say the results were inconclusive.  All the pads let through a reddish glow of light, and maybe the light was a tiny bit whiter/brighter around one of the ones I replaced, but it's hard to say for sure.  For now, I don't think it's worth the effort and risk of undoing and redoing my glue job, but I may return to this later.

 

6 hours ago, RAc said:

Another possibility is that one or more of the triangular wooden blocks that hold the reed plate in place has come loose.

 

I don't want to dismiss this possibility, but I'm not sure I see how it could affect the overall airtightness, as those parts are all internal?  I do see how it could affect the responsiveness of the instrument, though.

[David Barnert]

7 hours ago, RAc said:

Another possibility is that one or more of the triangular wooden blocks that hold the reed plate in place has come loose.

1 hour ago, Johanna said:

I don't want to dismiss this possibility, but I'm not sure I see how it could affect the overall airtightness, as those parts are all internal?  I do see how it could affect the responsiveness of the instrument, though.

 

I was thinking the same thing. When one of those blocks on my concertina came loose it caused notes in that corner of the reed pan to play simultaneously when any one of their buttons was pushed (ie., the chamois seal between the chambers failed because that corner of the reed pan was not firmly pressed against the underside of the action box). But it had no effect on the general air-tightness of the instrument.

[alex_holden]

1 hour ago, Johanna said:

 

I know you're kidding, but it occurs to me that hardware stores sell foaming leak-detector compounds for finding leaks in tires, gas lines, etc.  Would these be safe to use on the seam between the action box and the bellows frame, or is that a terrible ideal?

 

That's what my instincts tell me too - the gasket has clearly been through a lot, although I feel I've seen gaskets in worse shape doing a better job of sealing (and this one was doing a much better job until a few months ago).  I recall being told, once upon a time, that replacing a gasket is not really a DIY job (and the Concertina Maintenance Manual doesn't even mention it).  Is that still the prevailing wisdom?

 

I don't want to dismiss this possibility, but I'm not sure I see how it could affect the overall airtightness, as those parts are all internal?  I do see how it could affect the responsiveness of the instrument, though.

 

I don't think I'd like to risk the leak detecting fluid in case it damages the finish or leaves some residue behind. Replacing the gaskets isn't terribly difficult but it's quite a bit of work and I wouldn't do it unless I was sure it was causing a problem. Agreed that a loose corner block shouldn't cause air to leak to the outside world, only between chambers.

[Tiposx]

Replacing the gasket on the bellows frame is a fiddly job, even if it goes well. The leather bellows binding needs to be lifted up where it curls over the edge and overlaps the chamois gasket. After the gasket has been replaced then the bellows leather has to be curled back over and secured again. Another way is to completely remove the end binding, then replace the chamois, then re-bind. Not all bellows are suitable for this treatment. Another complication might be that one or more of the support blocks becomes detached when the chamois is peeled off. And so it goes on, what might be simple can become complicated.

Edited October 11 by Tiposx
Note that this was typed during Alex's post.

[Alex West]

For what it's worth, I think my fellow Alex's suggestion of one or more of the pads not seating properly is the most obvious cause of the issues.  However much you don't want to re-do it, that's to me the first place to start

 

Alex West 

[Johanna]

8 minutes ago, Alex West said:

For what it's worth, I think my fellow Alex's suggestion of one or more of the pads not seating properly is the most obvious cause of the issues.  However much you don't want to re-do it, that's to me the first place to start

 

Alex West 

 

So then, silly question, but how does one best separate a pad that's been glued with PVA glue, without breaking anything even worse?

[wunks]

As for leak testing compounds, save your money.  A little mild soapy water solution with an eye dropper can be used to detect gas leaks in piping connections.

[David Barnert]

27 minutes ago, Alex West said:

For what it's worth, I think my fellow Alex's suggestion of one or more of the pads not seating properly is the most obvious cause of the issues.  However much you don't want to re-do it, that's to me the first place to start

 

Alex West 

 

Here’s an idea: Before attempting to remove and re-glue pads, cover the holes under the suspect pads with tape (Scotch Magic Tape should be easy enough to remove without leaving residue, though there may be better choices) and see if that causes improvement in the air leak situation. If so, remove the pieces of tape one by one, perhaps occasionally re-taping one, testing in between, to narrow down which pads need attention.

[Geoff Wooff]

For  the  detection  and  pin pointing  of  leaks  I  use a Stethoscope,  bought  at  a flea market  as  part  of  a blood  pressure measuring  kit. Removing  the  'sounding'  flat   from  the  tube   end  one  can  use  the  device  to  locate  small  breezes    from  ill fitting  pads  ,   cracks in  the  wood  or  holes  in  bellows  etc.  I  fitted  a  small  diameter  nozzle  in  the  rubber  tube  to  increase  accuracy.

  

Edited October 11 by Geoff Wooff

[Johanna]

31 minutes ago, David Barnert said:

 

Here’s an idea: Before attempting to remove and re-glue pads, cover the holes under the suspect pads with tape (Scotch Magic Tape should be easy enough to remove without leaving residue, though there may be better choices) and see if that causes improvement in the air leak situation. If so, remove the pieces of tape one by one, perhaps occasionally re-taping one, testing in between, to narrow down which pads need attention.

Genius! Will definitely try that.

[RAc]

3 hours ago, alex_holden said:

Agreed that a loose corner block shouldn't cause air to leak to the outside world, only between chambers.

well yes, of course all of you are correct here, apologies.

 

However, for a reverse reasoning, I would exclude the pads because if the air would escape through leaky pads, that would be audible, right?

 

If the air loss comes without a sound and the bellows can be excluded, then there must be a leak in the space between the action and reed pans. My idea here would be to remove the action pan, dust all of the chamois and the outer rim of the case with a thin coat of colored chalk, then firmly press the action pan in place without fastening it, remove it and check to see if the chamois leaves even color traces on the underside of the action pan. Do not be too generous with the chalk and be careful when choosing the material (my first thought was baby powder) as you do not want major amounts of what can clog the reeds in your assembly.