Re: rotary valves


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Posted by dave on August 25, 2003 at 23:18:48:

In Reply to: rotary valves posted by david on August 25, 2003 at 22:12:47:

The problem with slow rotary valves is seldom the linkage. Much more likely it is either lack of the right kind of oil on the bearings, or if the horn has not been cleaned, or has been sitting a while, it might be due to a buildup of crud and oxidation just enough to cause the valves to drag.

My suggestion is to first try applying some oil to the spindles. A light oil is desirable, Singer sewing machine oil is about right, or you can buy something designed for rotary spindle bearings if you want to pay more for essentially the same thing (Yamaha and Hetman make oils for this purpose). To do the job right, remove the rotors, clean everything with soap and water, oil the spindles then reassemble. Try not to get the oil on the rotor, keep it localized on the spindle. Add an extra drop to the bottom of the valve (inside the cap) and a drop or two to the top of the valve at the spindle every now and then, and it will stay in good shape for quite a while; there is no need to disassemble the valve every time it needs oiling.

Don't confuse "rotor oil" with "rotor spindle oil". Rotor oil is pretty much unnecessary, it is designed to be dumped down the leadpipe or a valve slide and its purpose is to lubricate the rotor itself, but no extra lubrication is needed for the rotor. If the clearances are right, just the moisture in the horn will keep it sealed, and there is no contact between rotor and rotor housing anyway. Besides, there is a good chance that the rotor spindle oil will wash some grease down from the tuning slides, and make the problem worse. Also rotor oil is *much* too light to work as a good spindle bearing oil, and it will evaporate away. Don't use valve oil either, it is also too light and too volatile.

If you have an older tuba that hasn't been played a lot recently, and oxidation has built up on the surface of the rotors, oiling the spindles is not going to do the job by itself. Either take it to a repair shop, or do the cleaning yourself. Remove the rotors and use a pinch of rottenstone spread on the rotor(easily available at your local woodworking supply) or a very fine lapping compound, and lightly hand lap the valve in place, using water to keep the lapping compound liquid, then flush the horn and clean it with a good brush and soap, then oil the spindles as described above. You may have to repeat this a couple of times; test the clearance by hand spinning the rotor with the bottom bearing in place and seeing if it drags. If you can feel *any* high spots while hand spinning the rotor you have more work to do. To hand lap the rotor, I use a 1/4" collet in a small holder attached to the bottom spindle, you may have to look around and make something suitable (e.g. drill a 1/4" hole in a dowel, saw a thin kerf down from the end to split the hole, then put a hose clamp on it to tighten on the bearing...)

When you reassemble the valves make sure to put the parts back where they came (each valve, bottom bearing, and valve cap is identified as to the valve with punch marks), and make sure to align the witness marks on each bottom bearing. Also, tap the bottom bearing in place using a small brass hammer until the clearance (end play) of the rotor is just a few thousandths of an inch. If it gets too tight, tap the spindle the other direction. Tighten the bottom cap in place first, then back it off a fraction of a turn before you tap the rotor, makes it easier to set the end play.

Oh, one more thing. Ignore the instructions that are on the web in various places about how to remove the valve. i.e. *do not* try and drive the spindle out of the swivel (the part that the linkage attaches to) by tapping the screw. This will invariably cause damage to the threads, which are small and fine. Instead, use a pair of flat-bladed screwdrivers to lever off the swivel, using the casting that holds the rotor stops as a fulcrum. Works quite well and as long as you are careful and use a large, wide screwdriver, will leave no marks.

-Dave


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