There are a couple of peripherals remaining; this time I will discuss the valve boxes which contain an integrated stack “cutout” (or “cutoff”) and “Theme” activation design.

The cutouts are actually a twin set of valve boxes (at least in my piano they are)  which get mounted on the main trunk of the pump. As I mentioned in the previous post, when the music roll is over, the user switches from “play” to “reroll”. One effect of this action is that the cutout valves are activated, cutting off suction to the stack, which prevents any notes from playing during reroll.

The cutout valves are just standard inside valves, located at the inside top of the box. These valves are the gatekeepers of the suction to the stack. It’s basically a firm disc with a leather facing, on stem which is mounted on a wooden base. The base is glued over the oval pouch, which inflates when the valve is activated. In this case activated means “closed”; the valve is off (open) during play mode.

As you can see in the photo, there is some other stuff going on in the box as well. The Theme valve is packed in here too, at least on this piano (there was a certain amount of design variation, even by the same maker, from year to year). The Theme valve is an extra expression valve which is triggered by rolls which are coded a certain way, known by the name “Themodist”, or other variations.
The Theme coding in a roll corresponds to special “snakebite” holes located near each end of a tracker bar in a piano with this system.

In a Theme piano the stack and pump are divided in half (bass and treble), and when the valve is triggered on one or both sides of the pump, the corresponding side of the stack gets more suction and therefore plays louder. It does this by bypassing the “regulated” suction and connecting the stack to the full power of the pump. That’s about it!

Well, that’s the simplified explanation; HOW the valve operates is something a bit more complicated. Take a look at the following annotated image which is my interpretation (which I believe is probably correct) of how the valve works:

In evaluating the current condition of these boxes, the facings and pouches of the large valves seem* okay, probably due to the minimal exposure to atmosphere over the years. The small theme activation valve is a wildcard, I won’t really know until it’s up and running if the thing works.
The rub is that I would have to completely dismantle the valve box to rebuild that one small valve….which in addition to being rather tedious risks damaging the box itself.

So, in this case I am making a calculated decision to push forward with the box “as is”, with the understanding that the Theme valve may not work as it should. I do reserve the option to return at a later time to rebuild it, all I would lose in that case would be a couple of gaskets.

Depending on who you ask, the Theme function is either a cheap gimmick or an expressive feature to make a roll more musical. It adds a little bit but is still a far cry from the level of expressiveness in a reproducing piano, which has a much more nuanced method of expression.

*to be tested!