Purpose Of Reed Valve Restraining Pins?

[banjojohn]

Please can anyone explain why there are pins in the chambers (presumably to stop the valve curling or opening too far), but no pins on the valves on the insides of the reed pans.... What is to prevent these inside valves from curling or opening too far?

 

I have just been replacing some valves on Lachenal 32159 and noticed that one of the chamber pins was missing, however the valve in question was showing no sign of curling, resting very flat against the wood. Should I bother to replace this pin?

Edited December 30, 2015 by banjojohn

[Greg Jowaisas]

The pins do seem to aid in keeping the chambered valves closer to the underlying vents and therefore aiding reed response. However i believe their prime function is to keep the chambered valves from opening too far and flapping and slapping up against the pad board contributing noise each time they open.

 

BTW matching valve thickness, length and stiffness to particular reeds is an often neglected aspect of getting a concertina to play to its full potential.

 

Greg

[Stephen Chambers]

The pins should (hopefully) prevent the valves from curling up so far that they get right up into the pad hole and the pad closes on top of them, trapping them there, so that not only is the valve no longer performing its allotted task, but it's also causing a pad to leak.

 

I've seen, and fixed, the results of this happening a few times...

[d.elliott]

In addition to Stephen's comment above, there other and primary function is to stop the valve from lifting o far as to catch on the underside of the chamber wall gasketing and thus stay open, remember that on bellows push the initial air flow is a higher pressure than on pull.

[banjojohn]

Thanks Greg, Stephen and David, for your informative comments above... I will follow the instructions in your manual David, and use a cut down dress makers pin to replace the one which is missing....

 

On the subject of valves: I replaced a number of these last night in Lachenal 32159, ones which were 'slapping' during play, but also notably both valves on the F note which I had been attempting to tune in a recent video (posted on C.net). I had concluded in my video, that this reed was probably fractured as it seemed to be sounding weaker and flatter when returned to the instrument. I now believe that the problem lay in the valve, as the reed is now sounding as strong as it's partner and also no longer flat! Whoopie !! Result... A big thanks for all your posts to all 'C.netters', I have learnt so much from this forum!

[Bruce McCaskey]

I recently purchased a functionally new instrument (the first owner had waited three years for delivery but only had it a few weeks before deciding to sell it) that had very poor response on several of the lowest pitched push reeds. I tried adjusting the reed set without any positive effect, even swapping same-pitched reeds between push and pull locations (A for A, G for G) with the problem remaining on the push. It seemed to be the location and not the reed that was the problem. It was suggested to me that maybe the chamber had a resonance issue and perhaps it would help if I added something to the walls to reduce the size. I called the maker and discussed the response problem but he had no suggestions.

 

I was reluctant to explore making changes to the chamber, but while considing the possibilities I noticed that the pins over the valves for those reeds with poor response were clearly set closer to the valves than the others that responded well. Lifting the valves and putting them on top of the pins temporarily eliminated the response problems with those reeds. I called the maker again and this time asked what the criteria was used for positioning the pins during construction and was told there wasn't one, "we just kind of eyeball them."

 

That didn't tell me much as no criteria for the "eyeball standard" was offered, but It seemed to me they must be placed too low. I pulled the valve limit pins for the reeds that had exhibited performance problems and reinserted them higher, and of course positioned the valves under the pins once more.

 

The reed response problem was cured.

 

I am still surprised that the maker didn't have some sort of standard established for the placement height of the pins, nor did he suggest checking that height when I initially called to discuss the response issues. It appears to me that the general idea is to place them high enough that the valve can move far enough that it doesn't interfere with air flow past the reed. I'd guess that both the pin height and the material the valve is made of (a flexibility consideration) are factors in establishing the minimum and optimal heights.

 

Edited to correct the last line, replacing "reed" with "valve."

Edited January 1, 2016 by Bruce McCaskey

[banjojohn]

Thanks Bruce, this is most interesting... It just goes to show... Always something new to learn, and it seems this one was not understood by the maker of your instrument. What a simple fix for what would have been an incurable problem without this little gem of knowledge!

[Bruce McCaskey]

I re-read my prior post and realized I'd made a mistake in the last line and so corrected it.

 

Thinking more about valve restraining pins, I imagine that the factors involved in establishing the proper heights for those limiting pins involves at least four interrelated considerations rather than just the two I mentioned above.

 

First there's the air flow requirements of the reed. As the pitch lowers and the reed gets longer, I imagine the air flow rate required for good reed response and unmuffled sound becomes becomes higher.

 

Second, there's the height of the limiting pin. If it's set too low, the valve won't open far enough to permit the necessary air flow past the reed to permit it to respond and sound properly.

 

Third, there's the flexibility of the valve. I imagine that the free end of a more flexible valve will more easily bend further around/past the pin and so clear that portion of the airstream more readily. I figure that the free end of a stiffer (perhaps newer, thicker, dryer or lower grade) leather valve will bend less past the pin and so might be more likely obstruct the airflow, especially on a low set pin.

 

Fourth, there's where the pin is located along the length of the valve. If it's too close to the attached end, it won't impact air flow, but it also won't have much effect on restraining the free end to keep it out of trouble (twisting, fluttering and possibly getting caught under the pad). On the other hand, if it is placed too close to the free end, I suppose there's a risk that the middle of the valve might flex/bow out and permit the free end to slip out from under the pin. At that point, you'd have to take the end off to get access to put the valve under the pin again.

 

The above just represents my speculations on the topic, and isn't intended as anything more. Although I've owned several concertinas over the years, I don't make or repair them and my experience with valve limit pins is limited to just one instrument.

 

Although the image quality isn't great (it's a greatly enlarged small section of a phone photo), I've attached a photo that shows two reed chambers of the instrument I referred to in my prior post. Note the difference in the height of the limit pins. The chamber with the lower pin was associated with one of the poor-performing reeds. Raising this pin to the height of its neighbor cured the problem.

Edited January 1, 2016 by Bruce McCaskey

[Jody Kruskal]

Hi David,

 

Is this really true? "on bellows push the initial air flow is a higher pressure than on pull. " I've not heard that factoid before.

 

Why is that?

Can you elaborate?

How does this affect play?

I would think that "higher pressure" would result in a quicker response, or louder volume, or both. I can't say that I notice a dramatic difference in the sound between push and draw, but there certainly is a subtle one... hmmm. I always thought that the difference was because of the springiness of the bellows. Pushing moves toward the resting state of the bellows and so it's assisted. Drawing is a tad harder as it's pulling the bellows spring apart.

 

Perhaps there is an old thread about these questions?

[d.elliott]

I re-read my prior post and realized I'd made a mistake in the last line and so corrected it.

 

Thinking more about valve restraining pins, I imagine that the factors involved in establishing the proper heights for those limiting pins involves at least four interrelated considerations rather than just the two I mentioned above.

 

First there's the air flow requirements of the reed. As the pitch lowers and the reed gets longer, I imagine the air flow rate required for good reed response and unmuffled sound becomes becomes higher.

 

Second, there's the height of the limiting pin. If it's set too low, the valve won't open far enough to permit the necessary air flow past the reed to permit it to respond and sound properly.

 

Third, there's the flexibility of the valve. I imagine that the free end of a more flexible valve will more easily bend further around/past the pin and so clear that portion of the airstream more readily. I figure that the free end of a stiffer (perhaps newer, thicker, dryer or lower grade) leather valve will bend less past the pin and so might be more likely obstruct the airflow, especially on a low set pin.

 

Fourth, there's where the pin is located along the length of the valve. If it's too close to the attached end, it won't impact air flow, but it also won't have much effect on restraining the free end to keep it out of trouble (twisting, fluttering and possibly getting caught under the pad). On the other hand, if it is placed too close to the free end, I suppose there's a risk that the middle of the valve might flex/bow out and permit the free end to slip out from under the pin. At that point, you'd have to take the end off to get access to put the valve under the pin again.

 

The above just represents my speculations on the topic, and isn't intended as anything more. Although I've owned several concertinas over the years, I don't make or repair them and my experience with valve limit pins is limited to just one instrument.

 

Although the image quality isn't great (it's a greatly enlarged small section of a phone photo), I've attached a photo that shows two reed chambers of the instrument I referred to in my prior post. Note the difference in the height of the limit pins. The chamber with the lower pin was associated with one of the poor-performing reeds. Raising this pin to the height of its neighbor cured the problem.

 

 

Bruce,

 

valve pin / valve restriction and the impact on air flow is important and for experienced repairers quite well understood. Often your issue results from having the pins bent down towards the valve, bending then up or rotating them slightly so that they follow a plane parallel to the reed pan base is all that is usually is required,.

 

There are two other considerations:

 

on bigger valves there is often more than one pin, on big reed instruments, where double acting, there are often three pins, and I have seen four pins. The pins nearest the valve root are set lower than the pin nearest the valve tip to 'shape' the valve when it is blown open, This shape is a bit like part of a parabolic curve, so that the valve bends evenly along it's length.

 

The valve pins are often set at an angle relative to the chamber wall, usually pointing towards the tip of the valve. this again sort of makes the valve curve along more of it's length rather than hinge in one point. What is does do is force the valve to curl away from the chamber wall gaining clearance rather than loosing it.

 

Dave E

[d.elliott]

Hi David,

 

Is this really true? "on bellows push the initial air flow is a higher pressure than on pull. " I've not heard that factoid before.

 

Why is that?

Can you elaborate?

How does this affect play?

I would think that "higher pressure" would result in a quicker response, or louder volume, or both. I can't say that I notice a dramatic difference in the sound between push and draw, but there certainly is a subtle one... hmmm. I always thought that the difference was because of the springiness of the bellows. Pushing moves toward the resting state of the bellows and so it's assisted. Drawing is a tad harder as it's pulling the bellows spring apart.

 

Perhaps there is an old thread about these questions?

 

 

A new word for the new year: 'factoid'. Factoid, a fact first read on an android device? Actually I have just looked up 'factoid' : unreliable information made fact by multiple repetition.

 

This information is from initial personal observation over several early years in repair, which I then came to rationalise through my knowledge of pneumatics coupled with pressure vessel testing schemes and appropriate techniques and legislation.

 

Back to the point of the discussion. I referenced the initial energy on opening a pad on a pressurised bellow set because it may flip the valve further than one might imagine.

 

The energy released on a pressurised vessel is called the burst energy. Basically the pressure differential between compressed air in an enclosed vessel to atmosphere, and between a partial vacuum and atmosphere is far greater when measured a little away from the point of release. If you blow through a drinking straw the jet airflow projects far further than any detectable air flow at the same distance if you suck at the straw at. the same rate.

 

This really becomes important when setting up an English or Duet when notes in each direction need to excite at the same bellows pressure 'feel' in either direction. Also on big reed instruments, if the reed set is tight it is easier to stall a push reed on push than a pull reed. Anglos are less of an issue as the reeds on any button are different and usually have correspondingly different sized valves. On compression of the bellows the reeds tend to start sooner than on extension of the bellows, they have a bit more energy, burst energy, to start them.

 

 

Not a factoid, but a matter of physics.

 

 

Dave

[Bruce McCaskey]

Thanks for the insights Dave. Clearly there are several considerations related to controlling valve movement while ensuring proper air flow for the reeds.

 

The photo I provided in my prior post was the "before" view, that is, the as-made location and angle of the pins, and as you can see the pins were angled up and away from the valves. I suppose I could have tried leaving the pins mounted as they were and just increased the angle of the pins away from the valves (for the poor responding reeds) but I wasn't sure just what the maximum practical angle might be for those pins. I expect that if the angle were too steep the valve could slide off the pin and then perhaps hang up and not reseat.

 

Since the pins for those poor responding reeds were inserted noticeably lower than those on the reeds that responded well, I instead elected to pull and reinsert them at about the same height as the pins on the well responding reeds. I reinserted them at the same tilt-up angle as the others, and pointed the same direction.

 

As I said, my changes cured the problems with the poor-responding reeds and I think they are generally consistent with the considerations you mention Dave.

 

I've attached another photo (taken from a different angle) of the as-made location and angle of the pins, and as you mention, they are obviously angled in the direction of the tip of the valve.

[Dana Johnson]

 

Hi David,

 

Is this really true? "on bellows push the initial air flow is a higher pressure than on pull. " I've not heard that factoid before.

 

Why is that?

Can you elaborate?

How does this affect play?

I would think that "higher pressure" would result in a quicker response, or louder volume, or both. I can't say that I notice a dramatic difference in the sound between push and draw, but there certainly is a subtle one... hmmm. I always thought that the difference was because of the springiness of the bellows. Pushing moves toward the resting state of the bellows and so it's assisted. Drawing is a tad harder as it's pulling the bellows spring apart.

 

Perhaps there is an old thread about these questions?

 

 

A new word for the new year: 'factoid'. Factoid, a fact first read on an android device? Actually I have just looked up 'factoid' : unreliable information made fact by multiple repetition.

 

This information is from initial personal observation over several early years in repair, which I then came to rationalise through my knowledge of pneumatics coupled with pressure vessel testing schemes and appropriate techniques and legislation.

 

Back to the point of the discussion. I referenced the initial energy on opening a pad on a pressurised bellow set because it may flip the valve further than one might imagine.

 

The energy released on a pressurised vessel is called the burst energy. Basically the pressure differential between compressed air in an enclosed vessel to atmosphere, and between a partial vacuum and atmosphere is far greater when measured a little away from the point of release. If you blow through a drinking straw the jet airflow projects far further than any detectable air flow at the same distance if you suck at the straw at. the same rate.

 

This really becomes important when setting up an English or Duet when notes in each direction need to excite at the same bellows pressure 'feel' in either direction. Also on big reed instruments, if the reed set is tight it is easier to stall a push reed on push than a pull reed. Anglos are less of an issue as the reeds on any button are different and usually have correspondingly different sized valves. On compression of the bellows the reeds tend to start sooner than on extension of the bellows, they have a bit more energy, burst energy, to start them.

 

 

Not a factoid, but a matter of physics.

 

 

Dave

I don't dispute your observations. I have had similar ones. Not sure about your physics. The bellows certainly is a pressure vessel, but it doesn't matter if the pressure is negative or positive to get that effect. Positive pressure is limited by the spring pressure on the largest pad which becomes a relief valve above a certain psi. Negative pressure is limited by the ambient air pressure vs a complete vacuum. In actual playing, the positive maximum may be realized from time to time with either lightly sprung pads or vigorous playing, but few concertinas would withstand the 400+ pounds of tension ( for a 6"bellows, more for larger ) required to max out in the negative direction. I would suggest that our musculature is simply much better designed to press rather than draw in concertina playing positions, meaning it is easier to generate a rapid pressure gradient on the press in normal playing posture. Players who like to accent on the draw often develop a style where they either open the bellows by rotating their wrist as if using a screwdriver , or shift the free end of the bellows into the vertical where they can literally push down to open the bellows. Both techniques can generate similar pressure spikes to a normal press, though they limit the full use of the bellows. Given the proximity of chamber parts to the draw reed, it would not be surprising if they had some effect, but I would heasitate to predict what it would be.

Dana

[ttonon]

 

 

The energy released on a pressurised vessel is called the burst energy. Basically the pressure differential between compressed air in an enclosed vessel to atmosphere, and between a partial vacuum and atmosphere is far greater when measured a little away from the point of release. If you blow through a drinking straw the jet airflow projects far further than any detectable air flow at the same distance if you suck at the straw at. the same rate.

 

Not a factoid, but a matter of physics.

 

 

Dave

 

Hi Dave,

 

I'd like to comment on the physics of the issue you raised, and not on the differences in musical response that you experience with push and pull of the bellows.

 

I find the above paragraph you wrote confusing. Let me explain the physics the way I see it, in the hope we can arrive at a common picture. Let's first simplify by eliminating the reed and replacing it with a round hole, and let's consider only steady flow (no changes in time). With positive pressure in the (push) bellows, air flows from inside the bellows through the hole to the outside. Just downstream of the hole entrance plane, a jet forms, extending many jet diameters downward. The static pressure inside the jet is equal to the static pressure outside the jet - the atmospheric pressure outside the bellows. (This is not the dynamic pressure of the jet, which is equal to the static pressure plus an additional term proportional to the jet velocity squared.) There's an entrance region upstream of the hole, where the air velocity increases in moving toward and through the hole, reaching a maximum at the point where the jet forms (where the sides of the jet become straight and parallel). That is the point where the static pressure in the jet equals the static pressure outside the jet. At the entrance, air velocities are very small a short distance upstream from the hole, at roughly at a distance equal to a couple hole diameters.

 

With negative pressure in the (pull) bellows, the picture is a mirror image of the positive pressure case. When we replace the hole with a reed, the flow field is much more complicated, because of the modulation in air flow caused by the vibrating reed tongue and superimposed on the steady airflow. Notice also that the reed is in the wall of the vessel, not at a distance downstream from the wall, but in the location where any momentary jet may attempt to form.

 

If you agree with the above description, can you explain the physical point you'd like to make by relating it to this steady flow picture? If so, I think I can better understand what you mean.

 

Regards,

Tom

www.bluesbox.biz

[Discord]

On the subject of pins, I was recently told, only use brass pins.

Apparently steel pins can become magnetic and affect the tuning of steel reeds close by.

The pins already in my instrument are rough cut steel pins that are probably the original item. About a hundred years old.

I needed to replace a few missing pins and decided to use some nickel plated brass dress pins with the heads cut off.

Out of curiosity I tried them with a magnet and that was when I discovered that nickel is magnetic.

I have since bought a box of 100% brass pins and used these for the replacements.

 

I am a bit reluctant to replace all of the existing steel pins for brass at the moment.

 

Has anyone else heard of the need for brass rather than steel pins?

 

Cheers.

Edited May 12, 2016 by Discord

[Chris Ghent]

Next time I have an instrument apart I will magnetise a pin as heavily as I can and report on this. I don't expect to see much of an effect given the small bulk of the pins, the weakness of incidental magnetism and the distance from the pins to the reeds. I suppose the reed could become magnetic too. There is a harmonica which creates bent notes when you operate a slider which inserts a magnet into the chamber but I suspect it is a serious magnet.

[David Hornett]

I use accordion valves, leather with plastic backs, without pins right across the instrument. They seem to do a lovely job, providing the plastic does not get caught up on the leather chamber seal and produce its very own tremolo.

 

David

[Chris Ghent]

Preventing that from happening is one reason we use pins; the other is so long valves will not get sucked back through the par hole.