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While doing some research on the Dynamics Cut-Off valve blocks in Duo-Art reproducing pianos, I made a few interesting discoveries that I'd like to pass along. In the reference which is commonly referred to as the Duo-Art Collection, which was Extended and Revised in 1983 by AMR Publishing Co., there's an Editor's Note on Pg. 9 of the section that was written by Wilberton Gould which reads, "Continuous changes were made to the Duo-Art system. For Duo-Art mechanisms produced prior to 1926 and for additional information on all Duo-Art systems, refer to......", and then they list three other references, which are contained in the collection. With this in mind, I am going to attempt to clarify what I believe are some misunderstandings as it relates to the Dynamics Cut-Off valve blocks.
These devices are, in my opinion, very simple in design and function.
However, Duo-Art made three different versions of the component and nowhere in any of the references are those differences thoroughly explained. Making matters more complicated, all three versions are called by the same name. So, before I go any further, I'm going to give them names. First, there's the "Single Type". It has eight signal ports (or connections) and one vacuum supply port. Second, there's the "Double Type". It has sixteen signal ports and one vacuum supply port. Third, there's the "Double Duty Type". It has sixteen signal ports and two vacuum supply ports. I'll explain how they're connected and what purposes they serve later in this treatise.
All three of these devices utilize a simple principle and they behave like an inline air switches, which allow air to flow or not to flow. In a very real way, they can be compared to electrical switches that either open or close a circuit. Also, each individual pouch in the blocks can be compared to a trackerbar and a perforation in a music roll. At the trackerbar, there are numerous ports and each is supplied with a small amount of vacuum from the bleed in a valve. As long as the paper roll covers the bar, no air will flow into the port. When the perforation comes along, air starts flowing into the port and down to the valve, and when the perforation passed, the air stops flowing. As it relates to the Dynamic Cut-Off valve, instead of a piece of paper being used to cover a port, a piece of thin tan pneumatic leather is used to create a 'seal'. Using the same comparison again, the 'trackerbar' portion of the switch is a slice of a spherically-shaped piece of sealed hardwood and at the apex of the curve there is a 1/8" hole. (see: pouch-valve.jpg) The 'form' is embedded in a circular well such that the uppermost edge of the well wall is the same height as the hole at the apex. At the edge of the bottom of the well there is another hole, which is the same diameter as the hole at the apex. Covering the well is a piece of loosely fitting tan pneumatic leather such that if you were to blow into the hole from the bottom, the leather would puff up, sort of like a balloon. Another way to look at it is like the reverse of a normal pouch with very little dishing. (see: double-long.jpg) In each 'section' of all three devices, there are four valve 'chambers'