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Valve material- Natural material vs. sythentic


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Greetings--From talking with a friend today who has a concertina on order, this question popped to mind: The concertina he has on order has a myler (plastic-type material). valve. My concertinas ( Wheatstone English and Dipper Anglo) use leather material for the valves. Are there differences/advantages to the use of either material? -- Steven

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Typical rectangular Mylar has uniform thickness which is not ideal for reed valves as for to operate under low pressure they need to be very pliable, and under high pressure they need to be less pliable. Leather valves (we're talking hair sheep, the best kind) are selectively cut (usually punched) with a decreasing width from butt to tip which makes them less pliable as the air force increases.

 

In order to get a good range of variable stiffness from Mylar (and similar synthetics), most of those valves are layered with two or three pieces of material, with each successive one being shorter than the one under it. If it needs more stiffness than 3 layers they usually resort to a thin metal spine down the middle with a curled-up end.

 

beltrami224.jpg

 

Note the differences in the types of plastic and number of - and arrangement of - layers for the 1 1/2 octaves of reeds in that photo. A lot of effort goes into making plastic valves work well! Also note that each color of plastic has a different stiffness so that depending on how long and at what layer you arrange them in will give you a lot of control over how it operates.

 

One of the problems with plastic valves is that they tend to seat home with a very distinct "snap" or "tack" noise. Not really too noticable unless you're playing softly, but a lot of people don't like that. Leather valvles are quiet when they close (unless they're dried out and curled back in which case they'll make a light "popping" noise as they seat).

 

Another problem with plastic valves is that they tend to attract dust (static electricity?), and when they do, that fine coating of dust will absorb moisture with the resultant "slurry" making like glue to adhere the valve to the reedplate. I know this sounds extreme - like, how can that much moisture ever accumulate in my box? I have repaired (many) accordions that had notes that would not sound - to find that the plastic valves "glued" to the plates. And only the ones with significant grunge accumulation (smoky bars?).

 

Of course with traditional concertinas this may not be a problem as the valves seat against wood, not metal.

 

About the only good thing about plastic valves is that they are less expensive than leather ones (IMHO).

 

Note that cheap accordions have single thickness Mylar (and ilk) valves. Better ones have multiple thickness ones; really good ones have synthetic leather valves with several layers; the best have leather.

 

-- Rich --

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Rich really knows what he is talking about here, but I do have to say that leather is a pain in the rear end. It is far from an ideal valve material. Mylar ( polyester) valve materials have a lot of good characteristics. It tends to stay flat, and respond the same way over it's long life. The biggest problem I have with Mylar and that sort of valve is that it it too darn stiff. While a leather valve may vary from .040" to .010", a .002" Mylar valve is too limp and a .005" valve is too stiff. There are ways to adjust the valves by clever shaping of the valve to adjust it's bending characteristics, but that is a big pain and difficult to do well. While it is easy to find a piece of leather the right thickness / stiffness for a given note on a skin. the thickness jumps for Mylar are all to large. Going from .005" to .002" is more than a 100% change where going from .040 to .030" while much more of a difference in thickness is much less of a percentage difference in leather.

 

I have for a long time accepted that plastic valves had more "slap" than leather valves. After all, they are harder right? but after trying out well made valves of both materials ( that just happened to be in the practical range for .003" Mylar ) I actually found the Mylar valves to be a good bit quieter. ( these were highly customized valves, not the kind you find in your typical accordion.) They had a tendency to roll up and down rather than lift and flop back down as a unit. Good leather valves also roll to some extent, but as they operate, they tend to get more flexible at the root and bend more there and less at the tip, causing more slap as the valve comes down all at once. Tapering the valve helps, but has less useful effect as the valve softens from bending at the root, or hardens as the leather dries out.

 

I still use leather for my valves, but forever wish there were something better, more uniform, more stable, and more reliably available. So many problems are related to valves. Leather may still be the best material available, but it is far from good.

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I wonder if I could tack on a valve question to Steve's.Seems an appropriate thread.

I'd often wondered why valves were shaped as they are, as the slot is parallel

Rich answers it here.

a decreasing width from butt to tip which makes them less pliable as the air force increases.

I have noticed though that all Jeffries I've seen with original or very old valves,they are rectangular ( and probably hand cut not stamped)

Was this then an economy on Jeffries part or is it just less important on an anglo with concertina reads ?

Wheatstone english and duets from the same period have tapered valves.

Thanks Robin

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I wonder if I could tack on a valve question to Steve's.Seems an appropriate thread.

I'd often wondered why valves were shaped as they are, as the slot is parallel

Rich answers it here.

a decreasing width from butt to tip which makes them less pliable as the air force increases.

I have noticed though that all Jeffries I've seen with original or very old valves,they are rectangular ( and probably hand cut not stamped)

Was this then an economy on Jeffries part or is it just less important on an anglo with concertina reads ?

Wheatstone english and duets from the same period have tapered valves.

Thanks Robin

 

Straight for parrallel chambers. Tapered for tapered chambers. (less room at tip)

 

Plain and simple.

 

Geoff

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