Help Finding A Leak/leaks...

[John Sylte]

Hi everyone. I have been working on a 20 button Lachenal lately and have run into a problem I am having difficulty troubleshooting. The left side leaks. When I press rather lightly on the bellows without pushing a button, I can hear air escaping the left hand side (from inside the concertina ends). In the past, if air is escaping from a leaky pad (or a button that is too tall) I can barely touch the offending button and the note will continue to sound as I release the button and continue pressing the bellows... That is not the case this time. My pads are all airtight. I replaced the reed pan chamois leather (on the inside of the frames) and thought this would fix it, but I still am having trouble. What I hear is multiple high-pitched harmonics, so somehow air must be passing through multiple reeds, right? I think I did a pretty good chamois job, but maybe not? How do I pinpoint the leak? Certainly someone here has run into this before... HELP!?

 

Thanks-

[Shay Fogarty]

Hi everyone. I have been working on a 20 button Lachenal lately and have run into a problem I am having difficulty troubleshooting. The left side leaks. When I press rather lightly on the bellows without pushing a button, I can hear air escaping the left hand side (from inside the concertina ends). In the past, if air is escaping from a leaky pad (or a button that is too tall) I can barely touch the offending button and the note will continue to sound as I release the button and continue pressing the bellows... That is not the case this time. My pads are all airtight. I replaced the reed pan chamois leather (on the inside of the frames) and thought this would fix it, but I still am having trouble. What I hear is multiple high-pitched harmonics, so somehow air must be passing through multiple reeds, right? I think I did a pretty good chamois job, but maybe not? How do I pinpoint the leak? Certainly someone here has run into this before... HELP!?

 

Thanks-

Is the reed pan properly in place? Did you replace thescrew that holds the action board to the underside of the strap rail. there may be something between the bellows frame and the ends. Its a case of eliminatiting all possibilities. Hope this helps.

[Greg Jowaisas]

John,

Is there anything on the inside of the end pressing upon a lever? I was working on a metal end Lachenal that nearly drove me crazy until I realized a bushing board screw was protruding and pressing just enough on the lever beneath to cause a leak under bellows pressure.

 

You might check the corner blocks and make sure the reed pan seats tightly against the sound board.

 

It appears you are familiar with the perennial Lachenal problem of levers that are too high being depressed by the ends. Sometimes the same symptoms appear when a pivot post is loose.

 

Greg

[Wally Carroll]

If this only happens on the push, my first inclination would be to suspect a leaky pad. Before getting into potential fixes, the first thing to do would be to identify which (if any) pad is leaking. Here are two ways to find a leaky pad:

 

1) Put the instrument in your lap with the right side down and the left side facing towards the ceiling with the bellows open. Simultaneously close the instrument while pulling on each of the buttons one at a time (thereby pulling a tighter seal on the pads). If the sound goes away, you have found the offending pad.

 

2) If you still can't find the problem, you can try opening the instrument and putting a piece of masking tape over several of the pad holes from the bottom side of the actionboard to completely cut off air flow through these particular holes. Reassemble the instrument and see if the harmonic goes away. Move the tape around until you narrow down which hole is causing the problem. In fact, if you really don't think it is a leaky pad, you might want to tape over all of the holes initially just to check.

 

Wally

Edited October 10, 2008 by Wally Carroll

[John Sylte]

Great advice everyone, especially Wally, thank you. I taped all of the holes up expecting to find my leak but instead found that, thanks to freshly rebound bellows, it was very airtight. I untaped a couple holes and they both shreiked at me a little under higher pressure. So I was wrong in assuming the pads weren't the problem. Then I isolated a couple other holes, and a couple others, and it turns out most of the pads are allowing air to pass under higher pressure... It makes sense that if you push hard enough, air will have to escape through the pads at some point, but I am not convinced I am simply pressing too hard. My other Lachenals have not allowed air to pass so easily. The springs are the stock lachenal jobbers and seem to be doing a fine job. I just replaced the pads with materials from david leese. It all looks sharp and ready to go but for this leakiness. I'm stumped? Bigger springs?

[Anglo-Irishman]

The springs are the stock lachenal jobbers and seem to be doing a fine job. I just replaced the pads with materials from david leese. It all looks sharp and ready to go but for this leakiness. I'm stumped? Bigger springs?

 

John,

I've been having a similar problem with my "new" lachenal duet. "Ghost" notes, but only on 2 individual buttons. In my case, it is the springs. On the first culprit, I fitted a new spring. Problem solved. On the second one, I just disengaged the spring from the lever, opened it a bit, and re-engaged it. Worked too!

 

I noticed while doing this that the duet has levers of very widely varying lengths, but the springs are all much the same distance from the pivot. So by the laws of mechanics, the same weight of spring is going to exert more force on some pads than on others. The pads I had the problems with were on the longest levers. Probably all the springs are a bit fatigued with decades of playing, but it only shows on the long levers.

 

Hope this helps!

 

Cheers,

John

[Michael Marino]

taping the holes does work though I have used waxed paper in sections between the reed pan and the action to test for leaks that way. Though I would suggest a good bit of care be done with any of the very fine suggestions that have been given. My reasoning to that is it is possible to prsuurize the bellows or the right hand side and create a problem you did not have before hand. i have also built a dark box (hexagon in shape for the 'tina's that i use with a darkened room and a flex neck LED lamp. It shows even minor miss alignments of pads or a crack that you can't easily see with the naked eye and no contrast.

 

There are other options that will work as well and a few I use that explaining them is difficult for me to get the right words for what I am doing (nothing arcane just trying to put the words together properly so that a person reading it could properly understand what I am doing).

 

Hope all the help you have gotten from the fine folks here helps.

[Theo]

This device described by Bob Tedrow doers a fine job of testing pads for air leaks.

[Marien]

Apart from Bob Tedrow's tool mentioned by Theo,

taking up a bad habit can also help to find a leak.

The bad habit is smoking.

If you blow a smog of smoke on the suspected area and

push the bellows, you will see where the leaked air comes from.

[Leonard]

This device described by Bob Tedrow doers a fine job of testing pads for air leaks.

Looks good, but I'm a bit worried about all the blood stains on Bob's table...

[Pete Dunk]

I'm a bit worried about all the blood stains on Bob's table...

Perhaps Bob put a PA out of its misery.