Pump (part I): Trunk, Reservoirs, etc

The trunk is the main body of the pump system, in a pedal-operated player piano.

It is basically a long box of wood with holes (ports) cut in it, over which various pneumatics and bellows are placed. The trunk will contain:

  •  Exhausters: The exhaust bellows are the lungs of the player system; they are what constantly evacuate the atmosphere air from the system, to create the suction which in turn powers the system. Despite the fact that one pushes the treadles with one’s feet, the air is not pushed in to the system (a misconception), it is in fact pushed “out”. This is done by two sets of large flap valves. On the push motion of the pedal, the atmosphere from the system is drawn into the bellows, through the first one-way flap valve. The second step is that the bellows (which is under constant spring tension) closes, forcing the air which just entered to now evacuate via the second flap valve. More here.
  •  Reservoirs: as the name suggests these large pneumatics hold a reserve of suction to help regulate the airflow in the system. Otherwise the direct action of the exhausters would be too jarring and irregular. Unlike the exhausters (which are spring loaded to close), the reservoirs are spring loaded to constantly try to open. This makes them want to tend to constantly draw in suction, which is after all their job! They only have one duty, but it is an important one.
  •  Expression boxes and other peripherals: these have already been discussed in previous posts. On my pump unit, the soft and theme expression boxes are mounted directly on the pump, while the governor/accelerator is mounted separately on the underside of the keybed, connected by hosing.
  •  Treadle linkage: I will discuss this separately in an upcoming post.

Restoring: the first and most important task before reassembling everything is to clean and seal the trunk body. If the trunk envelope is not airtight, the piano will not play as it should. A leaky pump will be noisy and ineffective. Using your sealant of choice (traditional is shellac but I chose to use Phenoseal), go around the entire trunk box and check every nook and cranny where a joint is discernable. The surface of the wood itself is likely already sealed with black lacquer or shellac, but over time the joints may open up just enough to leak, so those have to be sealed up. If there are any splits or holes in the trunk they should be repaired (wood glue is suitable here).

Then it’s time to recover the exhausters and reservoirs (which you will have previously removed). If the boards were not damaged during removal from trunk or removal of old cloth, then they can be reused.

Let’s start with the reservoirs. You have removed the old cloth with heat, or water, or a power sander (let’s take it easy with that last method!). In the process of removing the cloth it’s best to leave the open end until last and take out the powerful V-shaped springs once the sides are first cut open. Do this carefully! Once cloth is gone clean off the old glue, which hopefully was hide glue. If it was a modern synthetic glue, you have my sincere condolences. There is probably leather gasket material left on the stationary board which needs to be cleaned off. Scrape off what you can, mechanically, without damaging the wood.
If there is residue left it could either be hide glue or thick shellac; glue comes off easily with water, but shellac will need denatured alcohol or methanol.

Check the condition of the hinge; replace as necessary.
Verify the condition of the springs, they are probably fine but if not replace them as well.
Before recovery I chose to apply a bolstering strap (about 2″ wide) across the open end, to help resist the strong tension from the springs, using the same ticking material as the hinge.
Reinstall the springs.
Prepare the pneumatic cloth, cut to rough shape then glue it back on.
Because of the large amount of surface area to cover with hot hide glue it is handy to have an iron to help set the glue, and smooth out any inconsistencies in the glue seam.  Trim the excess cloth with a new razor blade, after the glue sets up but before it hardens completely.

Copy and make a new mounting gasket for the stationary board, and if the reservoir has a panel cover (to allow access to mounting screws), make a new edge gasket for it, and set all aside for now.

Here are a few photos from the process:

pump mechanism (unrestored) removed from the piano
pump mechanism with the various valve boxes and reservoirs removed.
This process was made much easier because they had been attached using blotter paper gaskets.
Removing old dried shellac from the joining surface with methanol. The cling wrap helps to keep the methanol from evaporating too quickly.
Removing pneumatic cloth from the reservoir. Once the sides are open, remove the springs at this point — carefully!
All cloth removed from the reservoir pneumatic.
Repair or replace the hinge, and the spring felt.
Recovering the reservoir pneumatic. The last steps are to add reinforcing tacks, then a final overlapping strip of cloth on the closed end. This is done with the pneumatic closed to keep the pneumatic cloth from binding.
panel covers for exhauster pneumatics. Removing and replacing the edge gaskets.

Peripherals IV: Soft box

Like the Theme valve (discussed last time), the soft peripheral is a medium valve box with pneumatics which adds dynamic expression capabilities to the piano.

And like other expression devices on the piano, it is divided into a bass and treble side. Since it is a single box this means it sits smack in the middle of the pump. The soft expression feature is controlled by two separate buttons, which can be depressed at will by the operator.

soft control buttons on a player piano, located in front of keys

When a button is pressed, it opens a small pallet valve under the button, sending a “signal” of atmosphere to the designated side of the unit. This small signal activates a pouch of an inside valve, closing it and choking the amount of air flow to the stack, to a moderate degree. In other words, the soft feature is literally a “choke”. There is a pneumatic on the side of the box, which is in the path of the diverted airflow, linked through two ports. Unlike the valve it closes with a slight delay (it is spring loaded to resist); this is to make the decrescendo less sudden and jarring.

soft expression box for player piano with annotations

That’s basically it…the idea is that as soon as the button is released the airflow of suction to the stack (and hence the volume level of the piano) returns to normal immediately.

Here’s what the valve box (now with new gaskets and pneumatic cloth) looks like with the panel cover on it.

soft expression box with panel cover

And finally here it is mounted on the trunk, still open while I do some set up for testing with the pump…

soft expression box on pump unit, for testing

Peripherals III: Cutout + Theme expression valves

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.

Valve box featuring cutout valve (top chamber) and theme expression valves

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.

tracker bar detail with specific holes for tracking (red), pedal (green) and theme expression (blue)

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:

Theme expression box with captions to explain functionality

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!