Inner leakage when pressing some keys

[Vitto77]

Hi all

I'm restoring an old Lachenal. I've made new pads and new valves, and after some experiments and changes it seems to going better. 
I've noticed two problems:

1) on the bass side, closing without playing, I hear a perceivable air whiff, and I can feel it on face closing near the cheek. I thought it might be up to not well centered pads, and corrected it; up to the not sealing valves, and I changed the whole set wit more suitable leather. With new valves, bass side has improved a lot in responsiveness and volume, but air flow is still there (the area is around the right side of the hexagon (mostly, it seems, from the T5 and C5 keys); I've add a very soft chamois gasket on the old one, but whiff has not stopped yet;

2) on the treble side: when I press C#, C or G on the push (so, on the left side of the hexagon), bellows' resistance seems to fall, the feeling is quite like I would press a bit the air button at a time whit these keys. If I play some other higher notes, this seems not to happen, and notes play loud without that slight collapsing of the bellows.

What may all this depend on?

Thanks, have a good day.

Edited October 15, 2019 by Vitto77

[Rod Pearce]

Have you checked the bellows for leaks?

[Vitto77]

Hi Mr. Pearce, thanks.

I regret I forgot to mention: yes, it was all in good conditions, no light was seen from the exterior, but a micro-hole on a corner I've already patched. Anyway I think I've just spotted the problem with bass side, some minutes ago (question number 1): it seems that three of four reed slots are chipped at the end, the reeds fit pretty snugly but at the end the missing of portion of reedpan's wood leaves a small gap, leading on the interior of the bellows and letting air coming out, stealing air necessary for the full power of reeds itselves (and subtracting air from the whole system).  Sorry for having asked before understanding it, but it's the first concertina restoring for me (I'm actually a restorer, but I work on other items).  Any corrections are welcome anyway 

Second question stays open ? 
 

[charleschar]

For question no. 2, the problem may reside with the reeds themselves or the leathers rather than the valves. If much of the bellows' air is used when playing those three notes, the reed may be set too high above the brass plate. This may be the case if the reeds are especially quiet as well. Secondly, the leathers that cover the holes used by the opposite direction reeds may be missing or bent. This could result in quiet reeds and more air used than necessary.

[d.elliott]

I might suspect home made pads, and the grade of leather on the pad facing. but do check the spring condition, and the action set up. One potential cause on the pads with short levers is the state of the cross bushing through key's transverse hole. If it is too tightly packed so the arm cannot rock in the cross hole then it may be that the pad is not being held closed by the full force of the spring.  The other point to consider is the key's travel. When fully pressed into the concertina action box the key head should be around 2 mm above the action box end cover. when the key is released it should lift by a consistent 3.2mm on all keys, if the overall set is too high and the travel exceeds say 4mm then you can get the key binding and the same effect of air passing the pads will become  a problem.

 

You should also check the pad board for cracks or screw holes etc. and also around the padboard for shrinkage from the frame 

 

Dave

[Rod Pearce]

Back to question 1 - Are you saying that the instrument is airtight (no leaks) if you do not press any keys but try to operate the bellows?

[Vitto77]

@Rod Pearce

No, air flows locally from the reed plate and action plate in the area of upper right of the hexagon (looking it with handle below). I added a thin layer of leather between the head's chamois gasket and head's wood, but it still flows from there. I checked the inner valves, they seems to be right. Perhaps it's something about the pads, (by the way, pivots too are firm in the plate). 

 

[Vitto77]

@d.elliott

 

Thanks Mr. Elliott

I made a first set of pads with 2mm felt, card and leather (it's a thin, cloth like leather) with the smooth face down to the hole. They resulted too rigid (up to the kind of felt) and I tried making another set, using a 1.5mm black dense foam sheets (it was that stuff used for no-slipping purposes, from a diy shop). I know it's not traditional way, but I can't find the right kind of felt, so I tried this way for the moment. Generally these pads seem to work (altough I saw circle of reddish light around, watching it in the dark with a led torch inside. I don't know if this means risk of airflow, anyway I'm working at this beautiful old Lachenal to learn something, hoping to restore it the best i'll can do). I had to re-glue some of them, to have them well centered on the circular sign around the holes.  It may actually happened that these pads came out not so well, and other fits better.

I checked the padboard in a dark room, with led torch inside the bellows, and I spotted three points where gasket  was letting the light pass; I passed all with a knife back to make it more fluffy as suggested, and put some thin leather patch between chamois and head's wall, it seemed to work well. Neither cracks nor holes. 

I made valves from kid's leather. They seems to work quite well, I cut smaller ones from thinner areas, and bigger from thicker. They seems to be well laying on the pad, and acting rather quickly. I'm sure there is something much better, but they seems to  work in an acceptable way for now. It will be for personal use, so I can make some mistakes to be corrected in the future. I will check about the key's travel and the bushing, naturally I had not idea about it, so thanks again. 

(I was forgetting about, I integrated reed's slots in that area with wood, 'cause there was much space from the reed frame (from the half to the point) and chamber's wall, I thought that air might pass by someway. That didn't solve the problem, but reeds now fit more snugly.)

 

 

Edited October 16, 2019 by Vitto77

[Vitto77]

@charleschar

Thanks, I will check!

 

[Theo]

I agree with what Dave Elliott says about possible leakage through pads.  

 

A pad tester is a very simple and very useful device.  I made a very simple one from a piece of plastic rod about 18mm in diameter and about 75mm in length, you could also use wood or metal.  One end should be flat and smooth with a piece of soft leather glued on the end, and the whole thing has a 5mm hold down the centre.  To use it press the padded end over the pad hole from the opposite side.  Place you mouth over the free end and blow gently.  You should not be able to hear air passing through the pad.  Check all pads and adjust them until there is no air leakage.

[Vitto77]

@Theo

Thanks so much, it sounds interesting!
(a little off-topic: since I see you're from Gateshead, that remembers me when I stood three weeks in Whitley Bay for an English summer course, and we sometimes went to Gateshead. Is Metro Centre still there? Since we were about 15 y.o. we enjoyed it so much! This apart, Tyne and Wear is a so beautiful land sometimes I still miss!)
 

[Theo]

You are welcome here any time.  The Metro Centre is still here!  

And I wish to visit Italy again before too long, Castelfidardo of course.