Valve Material

[GaryKelly]

Hi all,

 

I've recently acquired a 'restored' Lachenal 48key English 'tina. The box is nice and mellow, perfect for playing in the evenings without disturbing anyone.

 

However... some of the notes are slow to speak, the box is 'breathy', quite unlike my Jackie 30-button. Further investigation revealed that the re-valving that the 'restorer' did was pretty poor. Some of the valves are too short for the slots they're meant to seal, others are squashed against the chamber wall and so aren't free to move as they should, and some had the valve pins missing and are curled away from the slots! Sigh.

 

I'm quite happy to re-valve the machine myself, all I need is suitable valve material/chamois.

 

Anyone know where I can obtain the 'proper' material, either direct in the UK or via the 'net?

[JimLucas]

I'm quite happy to re-valve the machine myself, all I need is suitable valve material/chamois.

Since you undoubtedly don't have valve-shaped leather punches, consider how much time it would take you to hand cut all those valves. If you're going to revalve it yourself, get valves, not valve material.

[Richard Morse]

You mentioned that you'd like to obtain the valves "direct in the UK", but your timezone info puts you in the eastern US? If you're on this side of the pond it would be easier to get valves from a place like The Button Box which sells concertina parts, including valves, which you may order by calling or e-mailing (they don't list their parts on-line).

 

Please beware that replacing valves means that you'll also need to have your box retuned....

[GaryKelly]

How strange, I'm definitely in the UK Can't seem to find a place where I can change my local time-zone.

 

Jim, I've found a chap in the UK who sells valves, and I've ordered some. But it would be handy to have a small sheet of the source material to be able to hand-cut where necessary.

 

I suspect that the reason some of the valves don't fit properly at the moment is because 'standard' sizes were used from a pre-fab kit of parts, and the standard sizes don't quite match the machine's requirements in all cases. This is probably why some of the valves foul against the chamber walls, and why some aren't quite long enough to cover the airway slot completely.

 

All in all, whoever did the 'restoration' did a pretty good job with the bellows and pads, but then bodged it with the valves (perhaps because they're out of sight?).

 

Gary

[Dan Stener]

Hello Richard,

 

I would like to understand dynamics and physics of the re-tuning necessitated by the re-valving process. Please explain a bit when you get a minute.

 

Thanks.

 

Be Well,

 

Dan

[Paul Read]

Valves are usually made from lambskin, I believe. Different thicknesses are used for different sizes (basically larger valve=thicker leather). You can get this at leather/leather craft shops such as Tandy here in N. America. The problem isthat you have to buy the complete hide - a lifetime supply.

 

I think Jim is right. Buy valves and spare valves for emergencies if you think you may need them.

[JimLucas]

... it would be handy to have a small sheet of the source material to be able to hand-cut where necessary.

I think you'd be much better off to take a standard valve and trim it, rather than try to cut a whole new one.

That should also help insure a close match on the appropriate thickness.

Your supplier should be able to provide individual valves, not just "standard" sets for a whole instrument.

[Richard Morse]

I would like to understand dynamics and physics of the re-tuning necessitated by the re-valving process.

While I'm far from the last word on valves and tuning - I and my shop have valved and tuned hundreds of concertinas... and we've observed that there seems to be some airflow dynamic that affects reed pitch (not to be confused with pressure dynamics which has a different and more minimal affect on the pitch).

 

Generally speaking (within certain parameters), the more restrictive the airflow path past the reed, the lower will the pitch of the reed sound. For instance if a reed in its frame is sounded to be exactly on pitch, it will sound about 4-5 cents flatter in the reedpan (the reedpan vent is smaller and deeper than the frame vent) and 2-3 cents flatter than that once you install the valve. There also seems to be a slight difference between pull and push reeds (less airflow restriction for the valves on the bellows side of the pan?).

 

Needless to say that revalving with exactly the same property valves and adhering them exactly the same amount of coverage would be nearly impossible.... You should expect a revalved (unretuned) box to be inconsistently off pitch over about 10 cents. Most likely much greater if you're using home-made valves.

 

There is so much work that goes into a good tuning (and much destruction done by a mediocre tuning/tuner!) that it makes sense (IMHO) to use "proper" concertina valves. They may be a bit pricey, but will perform and last far longer than any other kind, and keeping in mind that the valve (item/material) cost is only a fraction of the cost to retune a box.

 

So what are concertina valves? Traditionally (and still made and used for the best) concertina valves are made of hair sheep leather, specially tanned, skived, and punched out of certain parts of the hide along the grain for excellent flexibility, memory and seal.

 

How so? Note that they're not rectangular but trapezoidal with radius ends. This lets the valve bend more easily from the tip to the butt which means that there's incrementally increasing memory capacity toward the butt, right were you need that return "strength" the most (as it has to deal with all the valve "weight" from there back to the tip). Such uneven strength allows it to open with little pressure and close quietly. Also keeps it from developing a hinge-area weakness near the butt.

 

Hair sheep has a fairly spongy structure (much less dense than cow) which allows valves to be skived thicker which increases memory and longevity. Hair sheep "tooth" is also fine soft which makes for a very good and quiet seal.

 

I hope this info is of help!

[Richard Morse]

How strange, I'm definitely in the UK Can't seem to find a place where I can change my local time-zone.

If you click on your name in which appears to the left of your post, the link will take you to your profile page where you can fill out a lot of information about yourself - you can even add a photo of you (and your favorite box!).

 

When I first checked your page out earlier you hadn't filled out any of it though the "user's local time" said the same time my time is which is why I assumed you were here in the eastern part of the US (or Canada). Now I see that you updated your "location" to be Swindon, UK.

 

Looks like a glitch. Hello Administrators! Can you figure out what's up with this time anomaly?

[JimLucas]

Looks like a glitch. Hello Administrators! Can you figure out what's up with this time anomaly?

Not an error. You just have to know where to go to change the setting.

 

First, read all the steps in the following series (because once you perform the next step, you won't be looking at this page ). Then do them.

 

.. 1) Click on "My Controls" above (toward the upper right).

.. 2) On the page that shows next, click on "Board Settings", in the "Options" section at the lower left.

.. 3) And on this next page (upper region to the right) you should find a drop-down list where you can select your time zone.

.. 4) Once you've made the selection, you can go use the "Back" button (or menu) to retrace your path to this page.

 

You have to do this yourself, because (1) there's no way the Forum could include a database that listed the timezone for every location in the world, even if one existed, and (2) you might want to reveal your local time setting but keep your actual location hidden (my time zone could be Sweden, Poland, France, etc.). And I assume that the reason the time zone defaults to North American Eastern Time is that that's where Paul S. and his computer are, and the Forum software won't allow the time to be blank.

[Daniel Bradbury]

Hello Rich,

 

So, if you are tuning using a reed tuning aparatus whereby you slide the reedpan into a slot and tune, then when you return it to the instrument it will be a little off. I guess that the "Art" of tuning includes the ability to compensate between the tuning bellows and the actual instrument. That is fascinating! I really admire you all for not only the skill, but the art involved!

[Dan Stener]

Hello Richard,

 

Thank you for replying to my request for information. The explanation is fascinating. Never really thought of aerodynamics being applied in this way. Pretty complex little boxes!

 

With appreciation,

 

Dan

[GaryKelly]

Thanks all... and thanks Jim, I've updated my timezone.

[OLDNICKILBY]

Why make life so difficult just talk to Dave Leese, hes a lovely bloke and always ready to help and advise

Old Nic

[GaryKelly]

Tis from Dave I have ordered my valves.

 

Dave's website for anyone else who might be wondering.

[ttonon]

...and we've observed that there seems to be some airflow dynamic that affects reed pitch (not to be confused with pressure dynamics which has a different and more minimal affect on the pitch).

 

Generally speaking (within certain parameters), the more restrictive the airflow path past the reed, the lower will the pitch of the reed sound. For instance if a reed in its frame is sounded to be exactly on pitch, it will sound about 4-5 cents flatter in the reedpan (the reedpan vent is smaller and deeper than the frame vent) and 2-3 cents flatter than that once you install the valve. There also seems to be a slight difference between pull and push reeds (less airflow restriction for the valves on the bellows side of the pan?).

Rich, can you please explain in more detail what you refer to as “airflow dynamic” and “pressure dynamics?”

 

When the reed is mounted over a cavity, the airstream approaching the reed (in the case of opening bellows) and the airstream leaving the reed (in the case of closing bellows) is directed roughly normal to the airstream direction through the reed slot. With the reed operating without the cavity, these airstream directions are different, being much more in the direction of airflow through the slot.

 

It’s not likely, however, that such an airflow effect is the cause for the altered pitch. A more likely explanation is that air in the cavity acoustically couples with the air being set into vibration by the reed tongue. The cavity air provides a spring-like effect (capacitance) that feeds back on the piston (inertia) effect of the air vibrating in and about the reed slot, and the system acoustically "loads" the vibration more so than when the cavity is absent. This is typically what happens with a Helmholtz resonator, and is well understood among Physicists. The leather valve significantly alters the vibration of the air in the vicinity of the slot. Thus, new leather valves, for instance, will probably not bend away from the slot in precisely the same way as the old leather valves. Since the typical result is that the pitch is lowered with new valves, my guess is that the new valves do not bend away from the slot as much as the old valves. This greater proximity to the slot acts as an airflow restrictor, causing an increase in velocity of the vibrating air, which in turn increases it’s inertial effect, consequentially causing even greater acoustic load on the vibration, thus lowering the pitch.

 

Best regards,

Tom

www.bluesbox.biz

[Richard Morse]

Rich, can you please explain in more detail what you refer to as “airflow dynamic” and “pressure dynamics?”

I think of "airflow dynamic" as being the path the air takes and the things in that path which make the airflow change (constrictions due to the smaller pan slots, valve location and properties, path surface friction, pad operation...) and "pressure dynamics" as being the amount of air in that path (caused by bellows movement/time).

When the reed is mounted over a cavity, the airstream approaching the reed (in the case of  opening bellows) and the airstream leaving the reed (in the case of closing bellows) is directed roughly normal to the airstream direction through the reed slot.  With the reed operating without the cavity, these airstream directions are different, being much more in the direction of airflow through the slot. 

I'm a bit confused with your words there.... The airstream approaching and leaving the same reed is completely different in that a valve will keep the airstream from happening in one direction. So I guess you're talking about two reeds in the same chamber (cavity)?

 

What is "normal"? The direction of the airflow when in a "normal" situation inside a concertina? If so, then yes the airflow direction between in-concertina and out of concertina....

It’s not likely, however, that such an airflow effect is the cause for the altered pitch.

I don't think that the direction of the flow by itself is cause for the altered pitch, but the reduction of the flow (caused by restrictions of/in the airflow path.

A more likely explanation is that air in the cavity acoustically couples... Helmholtz resonator....

There has been a lot of investigation and debate about this issue. Personally I think that there is no significant Helmholtzian propensities in concertina construction. The frequency, physical chamber sizes, and math just don't coincide. The discrepancy is HUGE.

The leather valve significantly alters the vibration of the air in the vicinity of the slot. Thus, new leather valves, for instance, will probably not bend away from the slot in precisely the same way as the old leather valves.  Since the typical result is that the pitch is lowered with new valves

Not necessarily. I can install new valves which will raise or lower the pitch.

my guess is that the new valves do not bend away from the slot as much as the old valves.  This greater proximity to the slot acts as an airflow restrictor, causing an increase in velocity of the vibrating air, which in turn increases its inertial effect, consequentially causing even greater acoustic load on the vibration, thus lowering the pitch. 

Following that argument would mean that any increase in air velocity would lower the pitch of the reed. And to only a VERY small degree does it. Consider the pitch difference between playing very softly and very loudly which is many times the air velocity (flow) difference yet the pitch is altered very little (which is one of the great things about free-reed instruments!). Now consider the same setup but with a more restrictive (secured in place or "tougher" new) valve. The valve's restrictions will make a much larger pitch difference than the pressure difference will.

[JimLucas]

...the airstream ... is directed roughly normal to the airstream direction through the reed slot.

What is "normal"? The direction of the airflow when in a "normal" situation inside a concertina?

One of the meanings of "normal" is "perpendicular".

I think that's what Tom means here.