Sticky Piston Valves

[tuba_hacker]

And remember that new piston casings must have time to build up a uniform layer of oxide. Frequent use is the best procedure, plus keeping it clean and oiled. DON'T, however, polish the insides of the casings to bright brass, or you'll have to start the process over again.

Rick "13" Denney

Perhaps this is why the first valve on my Weril became worse after a chem clean?

Personally, I'm with Neptune. In all my years of playing trombones with an F-attachments, I've never had a problem with a rotary valve sticking or working slowly.

[Donn]

In all my years of playing trombones with an F-attachments, I've never had a problem with a rotary valve sticking or working slowly.

I have played a tuba with clock spring rotors that had a sticky valve. It would lock down, in a mechanical sort of way. I felt that it had something to do with the rotor linkage pivot, but couldn't prove anything.

[Dan Schultz]

1) Worn piston valves have INCREASED clearance.
2) Worn rotor bearings have DECREASED clearance.

Pistons will continue to operate but will be sloppy. Rotors will bind.

It seems to me that they'll rattle around in the bearings first, before they wear to the point where the rotor contacts the casing enough to cause damaging friction.

Rick "who has rattled lots of loose rotors that still worked, but noisily" Denney

You're missing my point, Rick. It takes very little wear on the bearings before the rotors will drag inside the casing.

[Dan Schultz]

I suspect Rick "gets it".

The topic, though, is "sticking".

I, like Rick, haven't encountered very many worn/noisy rotary valves that actually "stick".

You mean that a rotor binding because it's rubbing the inside of the casing isn't called 'sticking'?

Even though the original post aluded to sticking PISTONS, the 5th post spoke of a Mirafone 186... which of course, has rotors.

The point I'm trying to make here is that the elements involved in pistons and rotors are two TOTALLY different sets of dynamics.

[Rick Denney]

The point I'm trying to make here is that the elements involved in pistons and rotors are two TOTALLY different sets of dynamics.

I'm gonna get picky with you, in full knowledge that you know what you are talking about.

The dynamics of lubrication are the same. The bearing surfaces float on a film of oil. If the oil is wiped or washed off, the valve will stick because of metal-to-metal friction.

It's easier for the small surfaces of a rotor bearing to lose the film, because the force is higher. We counteract that by using heavier oil that builds a stronger film. But they'll wear faster if you run them dry. The heavier oil, even though it requires more force to overcome viscosity, still works because the bearing diameter is small and the linkage has considerable mechanical advantage on it. Pistons, on the other hand, have no mechanical advantage and large bearing surfaces and the oil must therefore be very light. And that means it has to be replaced frequently.

Your original statement (was it yours? I've lost track) suggested to me that you (or whoever) were arguing that rotary valves had less wear potential because the bearing surface was smaller. It's just the opposite.

Rick "whose Miraphone valves and worn and need heavyish oil to run quietly (no, it's not the linkages), but they do not stick" Denney

[Wyvern]

If well maintain, rotors, do not have to wear. My old Haag (Swiss made) Eb dates from the first half of 20th century and there is no discernable slackness in its rotors which still run smoothly and quietly (never sticking!) using old clockwork springs.

Having only three valves, its use is limited, but it comes out each Christmas carol playing.

[Dan Schultz]

The point I'm trying to make here is that the elements involved in pistons and rotors are two TOTALLY different sets of dynamics.

.... The dynamics of lubrication are the same. The bearing surfaces float on a film of oil. If the oil is wiped or washed off, the valve will stick because of metal-to-metal friction..... It's easier for the small surfaces of a rotor bearing to lose the film, because the force is higher. We counteract that by using heavier oil that builds a stronger film. But they'll wear faster if you run them dry.

That's very true, Rick.... and I'm not looking for an argument here. However... the can hear the wheels of some of the poster/readers turning. I suspect that folks are trying to apply the same theory to the outside of a rotor and to the outside of a piston. The outside of the piston needs a film of oil to isolate it from the casing and allow it to move freely. The rotor only requires a film of oil on the bearing surfaces. Even if the rotor bearings run dry, the rotor will never actually contact the inside of the casing..... for a while, anyway.

Now... there IS a matter that applies to BOTH pistons and rotors... a film of something (oil, moisture, etc) IS necessary to maintain a air seal between the rotors/pistons and the casings.