The reverse flow Unitype unit valve accordion pneumatic is a
three-eighths-inch wide pneumatic-valve single-row player piano action
brilliant double whammy in my opinion. That is a mouthful, if you now
can catch your breath, that is!
If you refer to patent number 1,783,319 by W.B. Tunstall, filed July
11, 1927, and read carefully lines 40 through 85, you will realise that
atmospheric pressure is what keeps the pouch pushing the valve into its
quiescent state, in reverse of what we are accustomed to. The single-row
three-eighths-inch wide accordion pneumatic is a stroke of genius in
The valves need not necessarily be a unit with the pneumatic, in my
view, as the rivet pull-type valve guide stem is a fine "miniature"
trick in a three-eighths of an inch "long" confine and would be maybe
easier to make slightly "longer". The circular sawed air channels are
very clever but not necessarily necessary, if valve and pneumatic are
separated a little.
There is an AMICA article possibly by Nelson Barden, according to Dana
Johnson, which is where I first found out about this last of the player
piano innovations, as radios and the great depression slowed player
piano manufacturing to nil. Myself, I am fascinated by the mechanisms
of all automatic musical instruments and this is one of the most
landmark but also obscure of all of them, and it worked very well.