Here are some photos of an accumulator I found in my parts bin.  
If anyone has an idea about its musical application or the musical 
instrument it came from, I'd like to hear about it.  It is decently 
constructed, mostly of wood.

Two pneumatics (which still work weakly) move the toothed disc this 
way and that.  In its full-right (counterclockwise) position (fig. 1),
the knife switch makes contact.  Its two terminals, one on the switch 
and one on the lever axle, have screw connectors (one screw is missing).

After 20 "inputs", the disc and its protruding rod have moved clockwise 
to where the rod disconnects the knife switch lever, which is now locked 
by a delicate swinging stirrup (fig. 2).

The disc can rotate 19 inputs counterclockwise but is locked from the 
20th by that stirrup.  A slight pressure on the tape-covered lever at 
the top -- perhaps a falling coin -- lets the spring-loaded brass lever 
close the circuit.  A pallet valve also operates at that time.  Due to 
the angled edge of the lever, the stirrup proves no obstacle to it 
moving in the other direction.

At the back, the disc axle (hard to see) is about one inch diameter 
diameter.  Pressing against it is a copper strip with pressure-adjusting 
screw.  I thought it may be an electrical contact, but the axle is wood.  
It looks like it provides drag on the disc's movement.

Perhaps my wife can use this mechanism to count how many piano rolls 
I buy in a month -- and have it cancel my credit card at the twentieth!

Tom Sendall
Piney River, Virginia

 [   accumulator figure 1
 [ http://www.mmdigest.com/Attachments/20/02/24/200224_191311_IMG_20200224_132440899.jpg
 
 [   accumulator figure 2
 [ http://www.mmdigest.com/Attachments/20/02/24/200224_191311_IMG_20200224_132737191.jpg
 
 [   accumulator back view
 [ http://www.mmdigest.com/Attachments/20/02/24/200224_191311_IMG_20200224_132959500.jpg