The effort here is to increase the amount of available information about this player system. If you have any additional pictures or information, please send them to John A Tuttle.
How it works.

Tim Geinert
Registered Piano Technician
Wapin Company, LLP

Unlike any system I have ever seen, the Kranich-Bach employs a (what I call) "through the valve" method of delivery vacuum to the striker pneumatic (note bellow). Initially, when I learned that the valve gap was a very shallow 0.020", I thought, 'How can this thing work efficiently?'. Then it dawned on me that the vacuum doesn't pass around a valve facing and through the gap to reach the bellow. It passes right through the opening. So, that started me to thinking about the square area of the air gap in a 'common' system verses the square area of the 'through the valve' system. Using some fairly common figures, I started doing the math. Let's say the size of the intake valve port is 1/2" and the gap is 0.035". The total square area through which air can pass is the circumference of the 1/2" hole (C = 2 ⋅ π ⋅ r), or 1.571", times the gap (0.035"), or 0.055 sq. in. Now, looking at the Kranich-Bach valve facing, you have an I.D. of 0.425" with a crossbar that's 0.135" wide. (see Fig 3.1) So, doing some simple math, we have the square area of a circle (A = π ⋅ r²), or 3.1417 x (0.2125" x 0.215") = 0.1418 sq. in. minus the area of (basically) a rectangle measuring 0.135" x 0.425", or 0.0574 sq. in. That leaves us with a total square area through which the vacuum can pass of 0.0844 sq. in. As you can see, even if the hole in the Kranich-Bach valve was smaller, the area through which the air can pass is still 50+% greater than with a common-type valve.

Now, concerning the narrow 0.020" valve gap, the question arises, 'Doesn't it impede performance?' Well, let's examine that. Since we have already eliminated the aspect of 'sucking' the air out of the bellows, the only thing that remains is letting the atmosphere back into the bellow. So, let's take a look at the I.D. of the (what is essentially the) exhaust valve port (which is part of the bellow). (see Fig 7) It has an I.D. of 0.485". With a gap of 0.020", the square area through which atmosphere can enter into the bellows is basically a long slit that's the circumference of the hole (C = 2 ⋅ π ⋅ r) times the gap (0.020"), or 1.52" times 0.020", which is 0.030 sq. in. Comparing that to the common valve, we see that it is 0.055 sq. in. So, based on those figures, one would have to assume that the narrow valve gap is problematic. What happens if we increase the gap to a more normal 0.035"? Then the square area is 0.053 sq. in., which is almost identical to the common valve. However, maybe we're missing one important part of the equation, and that is the size of the striker pneumatic. While there are no pictures that actually show the exact measurement of the bellows, in Fig 7 we can see that it is almost exactly 5" long and about 3/4" wide. If it's like most striker pneumatics, it has a span of 1-1/4". That equates to a working area (internally) of 1.406 cubic in. of air space. Comparing that to the size of a common striker, which measures 4" x 1-1/4" x 1-1/4", we find that the internal square area is approximately 2.125 cubic in., or just over 50% bigger. The point I'm trying to make is that it seems that the small gap is more than adequate to allow air to 'fill up' the bellows just as fast as the larger gap and a larger bellow. I admit that I don't have the math skills to figure these things out precisely. However, in terms of performance, the ability to suck the air out of a bellows at a very fast rate seems to me to be very important because the faster you can close the bellows, the more time you have you have for it to open back up.

Disclaimer: The opinions expressed above as simply that; opinions. No scientific tests were run. However, just based on the above numbers, it seems to me that the Kranich-Back system is more than capable of performing at least as well as most other systems, if not better. Signed: John A Tuttle

John
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