What's it for? How's it work

[bill]

In putting new stops on my Miraphone 184CC-5U, I discovered little adjusting screws in the bottom valve plates. When turned counter clockwise, they made the valves quieter and, in combination with the new bumpers, made the valve action very quiet, indeed. How do they work and why, when turning them clockwise, do the valves get noisier? This effect is counter intuitive to me. Can anyone explain this feature of this horn? Thanks.

[bill]

Thank you both for the explanation. It certainly works to reduce noise; I have never had a quieter rotary valved tuba. I can play with it to discover why it quiets when turned counter clockwise. Is it a reverse thread or ? ? ? Nice to have a resource like the Tubenet to get answers and education.

[TubaRay]

Nice to have a resource like the Tubenet to get answers and education.

Despite some folks' complaints to the contrary, I agree with you wholeheartedly.

[imperialbari]

My 187 has 'em. And that's what I'd always assumed they were for, but didn't really know for sure. I figgered as long as everything's working OK right now, I'm safe.

I understand you as if they are among the things you haven't screwed yet?

K

[iiipopes]

What bloke said. On my 1971 186 I don't believe they had ever been adjusted properly, and after I got it @ a year and a half ago, upon doing what bloke posted, the old lever arm linkage just quieted right down. Also, with just the slightest adjustment as bloke said, backing off just enough to have free travel, when you fill up the little well inside the bottom cap that the little screws thread through with sewing machine oil (you can get a 4-oz bottle of real Singer brand at WallyWorld for @$2), when adjusted properly capillary action will keep oil on the bottom bearing and help keep the rotors from wearing their bearings. The tolerances are very tight so they don't leak oil.

[MaryAnn]

Thanks....this weekend I'm going to "fix" that slightly clanky first valve on my 184 CC.

MA