Tracking Device: Rebuilding and Testing

This is going to be a lot shorter than the preceding post, for a couple of reasons.

Firstly, half the battle with a component like the tracking device is simply understanding how it operates. You can’t do proper rebuilding and testing/troubleshooting without this knowledge.
It took me a few days of fairly steady thinking on this topic, for it to start to sink in.

The other thing is that there is not a lot new here, in terms of components. I’ve covered pneumatics, I’m probably not doing pouches (however this is covered extensively in the Reblitz book), and I will specifically cover gaskets (simple) and valves in future posts.

Like the other components, good sealing is a must for proper function. This means the internal channels, the recovered bellows, the mating of the primary valve facings to the box, and good gaskets.

Once all this is done, it’s a matter of reassembly and testing. Here’s what it looks like back together:

Tracking device, nearing completion

And so let’s make sure it does what it needs to do.

First get a suction supply going, to test. In a perfect world you have a test pump from an old reproducing piano, but barring that, a regular shop vac will suffice (it’s what I used). Just regulate the suction so that you are in the 5″ water range (a vacuum dial gauge is good for this, or a home made water vacuum gauge). I made a laughably cheezy regulator, with a clothes pin and some elastics, to hold a piece of tubing a little bit outside the mouth of the vacuum. MacGuyver would be proud!

The drawback to testing with a vacuum is the noise. Apart from being generally grating, it also makes it difficult to hear leaks when troubleshooting. But, we must use whatever tools at our disposal.

Hook up the suction supply to the appropriate nipple on the box (it should be the one that is not otherwise identified). Then run the following series of tests:

1) Close off all 4 inputs (you don’t need to tube to an actual tracker bar to do this). Is the system balanced? You should see the pneumatic cloth get sucked in slightly in the bellows, but other than that, they should stay pretty much where they are. More on that in a moment. Assuming all good, continue.

2) Open the outer holes. Still balanced? Good!

3) Open the inner holes too, all holes open. Still balanced? Okay!

These tests check the balance of the pneumatics, if the bellows list to one side or another, or if they are otherwise not behaving identically to each other, we have a problem! The problem is a leak somewhere, so you’ll have to track it down and fix it. Do it now, show no mercy to leaks whatsoever. It will not ever work if it leaks, so if it means taking everything apart and checking each component separately, just do what it takes!

Once we have established balance in equilibrium, let’s check it in disequilibrium.

4) Close all holes again, then open just one outer hole. The bellows should track accordingly, moving smoothly in concert to one side. When you cover the hole, they should return to default halfway position. If they move quickly but don’t return reasonably quickly, this is a troubleshooting tip, likely a blocked bleed. Try the other outside hole in the same manner.

5) Same as step 4, but concentrate this time on only opening each outer hole (not at same time) just a little – halfway or less. The bellows should still react and begin to shift as soon as the hole is opened partially.

6) Cover only the inner holes, and repeat steps 4 and 5, one inner hole at a time. The bellows should again perform the same way.

Assuming it does all these things well, you should be good. But if there is something which makes you squirrelly happening now, just check again and again, repairing if necessary, until it looks like it should.

One thing I noticed on my first attempts, was that the right pneumatic would noticeable jerk when getting suction signal. It is a quirk of the design that the pneumatic is only mounted on the shift box with a single screw. This is not ideal from a “no motion” perspective, so I had to dismount it (which ruined my gasket, it had to be cleaned off and replaced), then check for flatness, and then make sure the pneumatic sits perfectly straight on the box, supported equally on both top and bottom, when you glue (or shellac) the gasket back on.

Thankfully the pneumatic had an access port for the screw, so I was just able to open that up to pop off the pneumatic, I didn’t have to ruin the the recovery job I had done.

This does remind me however, that there are possibilities for some real bouts of tedium and frustration when troubleshooting. What’s more is that the closer you get to the end, the chances of time-wasting increase, unless you take the time to really check your work at every stage. I must repeat this mantra to myself constantly!

Here’s a video of a testing session I did:

So, that’s basically it! Just reattach whatever mounting blocks or other hardware to the unit, and set it aside until whole action reassembly.

On to the next thing!

Actually, let’s take a quick side tour to gaskets….TBC

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