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Four-Hole Tracking System
Theory of Operation

Occasionally, I receive letters like the one just below:

Hi, John,

I got the piano off life support (shop vac), and also got the tempo control adjusted, and I'm really enjoying getting involved with the many adjustments needed. It's a tad harder to pump now, but that was expected. I'm having a bit of a problem with the Tracking Device. I went completely through it and inspected every part of it. It's connected to the tracker bar via lead tubes with elbows shellacked into the tracker body. I found that when it's in operation, it responds to the system by staying hard down. No amount of covering the tracker bar holes has any effect on its position.

I didn't replace any of the gaskets when I had it apart. I had to recloth the side, which I wasn't sure of because there are no instructions in A.Reblitz book on that part of the repair. I glued the entire side and placed the cloth to cover the entire side of the control. Hope that was right The old one was split at the joint. There are two drilled passages in the face of the control, but they're covered by the cloth. Don't understand that set up at all. Maybe it's supposed to be a hinge when the control is split

One of the pouches looks bad, another looks like it might have a hole, but I'm not sure. Please send me enough pouch material to do at least 4 pouches. What do you think about replacing all gaskets in the control with 1/16" cork? I found some real nice tight grained cork at a hardware store in town. Another question is, Are the primary valves and inside valves supposed to be set as close as those in the action? There's no mention in the book.

Well, sorry for the longwinded note, but at least I didn't call you with this.

Regards, Fred

Here's how I responded to the above concern:

Hi Fred,

Tracking mechanisms can be tricky...... It sounds to me like there is a leak in a signal line leading to a pouch. Or, a pouch isn't dished deep enough, which prevents the valve from seating. You might also have a leaky valve. Obviously, if there are any leaks in the pouches or valves, the mechanism cannot work correctly.... It is imperative that the valve block and bellows be 100% air-tight. The slightest leak will cause the device to malfunction.

I've repaired numerous tracking devices without replacing the gaskets. However, they are always replaced when the device gets rebuilt.

I will assume that you checked the bleeds and that they are clean. I will also assume that you checked the air-tightness of both bellows before attaching them to the valve block.

Also, you can check the operation of the valve block before you put the bellows back on. The process is a little difficult to put into words. You have to understand how the block works. Basically, you open and close the signal ports leading to the valves as would happen when the paper opens and closes the ports, and you see how the device responds. (See page 27 of the Service Manual for proper valve clearance and cleaning.)

One of the reasons I haven't attempted to create a webpage about testing, repairing, and rebuilding a tracker mechanism is that for starters there are four basic types. Those four basic types are then sub-divided into various smaller groups that have slight design differences. Explaining how each one operates and how to rebuild and test them would likely fill a small book.

If it's of any help, the four-hole tracker device is something like two and-or circuits in transistor theory. When the two inside holes are closed, the two outside holes control the bellows. When both outside holes are open, the two inside holes control the bellows. In other words, opening the two outside holes changes the state of the associated valves and turns control of the bellows over to the other two valves. You can watch this happen. When all four holes are closed, both primary (or outside) valves are closed, and vacuum is applied equally to both bellows, keeping them centered. As one outside hole on the trackerbar opens (right or left), this opens (or activates) the associated valve and it changes state. This turns OFF the vacuum to one bellow, causing the other to draw further IN (or collapse), which adjusts the position of the music roll. In the condition when both outside holes are open, both primary valves are activated (or UP), and an equal amount of vacuum is applied to both bellows via the secondary valves. As one of them gets activated, by opening a hole on the trackerbar, it TURNS OFF the associated Primary Valve, which in turn shuts off the vacuum to the associated bellow and allows the other bellow to collapse, adjusting the position of the roll.

It goes without saying that the four-hole tracking device is the most complex device in any regular 88-note player piano. Getting a grasp of the theory of operation is somewhat difficult since it is kind of backwards compared to other pneumatic devices, i.e., when it's Off, it applies vacuum to the bellows.

Hope this helps.... I'll send you a piece of leather for the pouches. The cork gasket material should work well as long as it compresses slightly. If it won't compress, then it might leak a tiny amount, which will cause a problem. The gasket must compress to handle any slight irregularities in the wood. BTW, the cloth cover is basically there to create an air-tight seal over that part of the block. However, if it is glued on with hide glue, it can be relatively easily removed to access the air channels for cleaning. Occasionally, a bleed will get very clogged such that the trackerbar pump can't clear the bleed. In such cases, the cloth can be removed and the bleed cleaned manually.


John A. Tuttle

Position Indicator Transposing Trackerbar Knurl Knob

For more information about roll tracking problems and solutions, see:

Tracking Problems - Click Here
Testing the Player Piano - Click Here
Adjusting Pneumatic Finger Trackers - Click Here
How To Operate a Player Piano - Click Here

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John A Tuttle

Now Playing: See'n You Rumba written by John Tuttle. It's not a Rumba, I just love watchin' her move!....

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