TubeNet

I own a bunch of brass instruments. On some instruments the valve pistons do not rotate as easily as they travel up and down. I never gave it much thought.

However, I have one instrument that has valves that are very difficult to twist in their cylinders. One of these valves is so resistant that I cannot turn it using finger strength alone. All of these valves operate just fine; they are fast and seal well.

So I don't have a problem, but I am curious why this condition exists, and also what causes it in the manufacturing process?

(In my experience this condition is more likely to be present on tubas than trumpets)

Hup

Because the "problem" on my tuba did not affect its playability, I was not in a rush to correct it.

However, yesterday I finally pulled the valves and let them dry out. The pistons looked fine. I couldn't see into the cylinders well enough to see if there was a coating.

I cleaned the pistons and cylinders with Lime-Away and reinstalled them. The difference was striking. Whereas previously the pistons would not rotate easily (and one would not rotate at all), they now turn with minimal effort.

I did not notice a difference in the playability of the horn or the speed of the valves.

I think it's pretty clear that Bloke's diagnosis was correct.

Hup