As far as I have been able to determine, there are three types of Duo-Art "Cut-Off" Pouch Switches. I refer to them as the 'Single Type' (8-port + vacuum port), the 'Double Type' (16-port + vacuum port), and the 'Double Duty Type' (16-port + two vacuum ports). For accuracy sake, Aeolian refers to these switches as Dynamic Cut-Off Valves or simply Cut-Off valve blocks, not On/Off pouch switches. Personally, I think it's easier to refer to them as switches than valve blocks, and I created my own names for them to distinguish one from another.
As stated on the Tubing Diagram for Duo-Art Grand Reproducing Action -1925 Model -Top View -Above Key Bed, "(1) On models 1924 & earlier, a second Cut-Off valve block similar to Unit "X" is used to cut-off notes 1-2-3-4 & 85-86-87-88 when Duo-Art is in the "ON" position (Unit "W") The control line of this unit tees into Line (124). (2) On models 1925 to the end of production... the above notes are not used as show on this drawing." (Mind you, this diagram is stated as applying to the Grand Reproducing Action.) I call the switch in the grand action tubing diagram the 'Double Type'. Obviously, the rational for having two Dynamics Cut-Off Valves was because units made after 1924 had an 80-note stack. (see post-1925-switch.jpg) Prior to 1925, they had an 88-note stack. However, it's extremely important to note the operative word in the explanation of the switch. That word is "similar". In fact, as you will see shortly, the switch is quite different.
The tubing configuration of the "upright" full reproducing models can be seen in Illustration "E" of the 1927 Duo-Art Reproducing Piano Service Manual No. 3.(see upright-switches.jpg) Note that this Dynamics Cut-Off device, which I call the 'Double Duty Type' switch, is quite a bit different from the switch in the post-1925 grand piano diagram. Unlike the grand switch, which has only one vacuum supply port, the upright switch has two vacuum supply ports. So, even though the switches look 'similar' (they both have 16 signal ports), the way they work is quite different. Side Note: Referring to the Duo-Art Collection, there is a section that was written by Wilberton Gould for 'The Tuners' Journal' entitled "Player Piano Mechanisms". On Page 2 of this treatise, Mr. Gould explains the operation of the Duo-Art cut-out pouch blocks. He writes:
"Note holes 1, 2, 3, and 4 at the bass end and 85, 86, 87, and 88 at the treble end have each directly above them a perpendicular oblong port. These oblong ports are the accordion dynamic control ports and are connected by tubing to the Duo-Art cut-out pouch blocks directly behind the spool box. These blocks contain a series of four pouches on either side of the blocks, one on the bass end and the other on the treble end, and are connected to the supply from the Duo-Art cut-out block on the left-hand end of the spool box; they are marked "Duo-Art On" and "Duo-Art Off." With the Duo-Art lever at the "On" position, atmosphere is admitted to the top side of the note pouches on the blocks marked 1, 2, 3, 4 notes and 85, 86, 87, 88 notes; this inflates the pouches' and cuts off the note holes from the tracker bar. With the Duo-Art switch at the "On" position, atmosphere is admitted through any one of the accordion dynamic control ports above the note ports, passes through the pouch cut-out block, thence to the accordion primary valve box, from there to each of its respective primary valves, then to each of the accordion dynamic pneumatics on the expression box....."
In my opinion, Mr. Gould never dismantled one of these Dynamic Cut-Out valve blocks. If he had, or if he had considered the basic operating principles of a pouch valve, he would have known that only by applying vacuum to the upper side of the pouch would the pouch inflate. In turn, once the pouch was inflated, the signal from the trackerbar could pass through the pouch well and on to its associated pouch and valve. (See signal-path.jpg... Note the red coloring between the two holes in the pouch well. They show the path where the air flows from one hole to the other.) If atmosphere is applied to the top side of the pouch, it will not move, and the vacuum from the bleed in the associated valve will 'pull' the pouch over the signal hole, cutting off the path of the vacuum to the trackerbar.
When you consider what it says in the note in the grand tubing diagram about Unit 'X', you would naturally assume that one of the switches controls the expression tubing and the other controls the note tubing. However, that assumption would be incorrect because as it also says in the note, "The control line of this unit tees into Line (124)". That being the case, it means that the same vacuum source which turns the expression on or off also turns the notes on or off. If that were possible, it never would have been necessary to invent the 'Double Duty Type' switch, which uses one vacuum source that is alternated between the expression side of the switch and the note side of the switch by the the Duo-Art On-Off switch in the spoolbox.
Now, we get to the tubing configuration of the upright Half D-A model with Duo-Art On-Off switch (in the spoolbox) which utilizes yet another type of switch, which I call the 'Single Type' switch. (see half-d-a-switch.jpg) By comparison to the other two switches, this is a very simple switch. It has only one simple function, and that is to disable (or turn off) notes 1-2-3-4 & 85-86-87-88 when the user is playing a Duo-Art roll. The switch serves no other purpose. It is, in fact, like one half of the 'Double Duty Type' switch. It has only 8 signal ports (and one vacuum supply port), unlike the other two switches, which both have 16 signal ports (and one or two vacuum supply ports). Also, in all my research, I found that the Half D-A system is the only one that utilizes both a Double Duty Type switch and a Single Type switch.
In terms of their internal construction (or design) all of the switches work exactly the same way. The port leading to a valve, whether it is a note valve or an expression valve, is connected to the center area of a convex shaped area which is inside of a pouch well. The port leading to the trackerbar is positioned at the edge of the pouch well. (see on-off-1.jpg and on-off-2.jpg) Also, all four of the pouches within each section of a switch share a common vacuum channel. When there is no vacuum being applied to this common channel, the vacuum from a respective valve pulls the pouch 'down', covering the hole in the middle of the convex area, and that in turns prevents the atmosphere, which would be available if a perforation in the music roll passed over the respective hole in the trackerbar, from entering the port at the edge of the pouch. (In a sense, it's exactly the same thing that happens when a perforation passes over the trackerbar.) Now, when vacuum 'is' applied to the common channel, all of the pouches 'puff up' (or 'inflate') which allows the signal (atmosphere) from the trackerbar to 'pass' through the pouch well from the hole at the outside edge to the hole in the center.
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