Tubing + Testing (Round 5)

It’s time for tubing — yes!
This is a sure sign that we are approaching the end of the project.
On a double valve stack, the tubing (or retubing) is effected at the end of rebuilding, when we know the valves and pneumatics all work.

This is another task which is pretty straightforward, but still needs a degree of care and planning.
It’s a question of both cosmetics and functionality.
If the tubing is stretched too tight, it may kink near the nipples or come off prematurely.
If it is too loose, it may kink on itself, or get caught in the piano action backchecks.
So, get it in the Goldilocks zone, and make it “just right” in terms of function and appearance.

The smaller size from the tracker bar to the nipple board (piano notes) and to the shifter valve box are usually size 9/64″ inner diameter. The expression and supply lines may be a larger diameter size like 3/16″, 7/32″ and so on. Measure the tubing based on the nipple fitting on which it will need to live. And note that while tracker bar tubing is generally sold in 100′ lengths, you actually need at least 140′ to complete a whole stack – ask me how I know this!

Tubing the stack nipples to the tracker bar. A note that the top row of tracker bar nipples corresponds to the even numbered notes of the stack, helps keep me on track (to avoid mistakenly skipping a nipple)
Stack tubing done!

The tube or hose should be barely snug on its fitting; enough so that it will not fall off accidentally, but not tight to the extent that you have to use a lot of force to push it on. For smaller diameter tubing (e.g. tracker bar), what helps is a bit of lubricant when trying to get it in place. A liquid polymer used for piano work, will serve well for this application, or failing that, good old human spit also does the job! This makes the job easier, and also safer for the piano, as it is not so difficult to inadvertently bend or break the long and delicate nipples on the back of the tracker bar. This preventable scenario is to be avoided!

In the event that your stack still has the original lead tubing, and said tubing is still in good condition (not deteriorated or crumbling), it can continue to serve if you feel it is safe to do so. If there are problems or damage that are evident, it’s really best to replace wholesale with neoprene tubing (again, working safely with the lead), instead of trying to do extensive and uncertain repairs to the old lead tubing.

Once everything is back together, it’s time for the final bench test of the stack. Hook up your suction supply to the stack and shifter device, with a vacuum gauge for calibration. Put a music roll in the spool box and wind it down onto the takeup spool. If you have a diagnostic test roll, this is an ideal choice. Testing the notes sequentially will help identify problems quickly and accurately. Fire up the suction and manually advance the transmission gear so that the roll plays through its notes. Make sure to check which note is the first on the roll — not all test rolls play 88 notes!

As before, if all notes work well, with good actuation and repeating, at various “tempi” (feed rate of the music roll), and if the shifter device keeps the paper tracking as it is supposed to, and you can do all this at 7″ of IWC suction, you are in good shape!

Here once again is Bruce Newman demonstrating what a properly restored stack looks like on the bench.

If you haven’t done so, finish assembling the spool box and any other components, to get the stack ready for its new home in the piano.

Before putting stack back in, this is the time to address any outstanding issues with the piano. Give the piano a good tuning, and voicing, if necessary. Double check the regulation and performance of the piano action. You can also check the functionality and regulation of the pedal pneumatic at this time, since it is easier to make those adjustments now.

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