Tightening rotary valve springs

[anotherjtm2]

I would like to change the spring tension so that the valves spring back more quickly. I don't have the right kind of scale to measure the tension, but increasing it by maybe half again seems about right. If I take the ends of one spring that rest on the bar, and pull them around one more turn, to the other side of the bar, and hold them in place with one hand, the added tension on the key is about what I'd like.

So.... is it reasonable to do this with the springs that are there? My concerns are (1) that an extra turn on each side of each spring will be too crowded on the rod between dividers, and (2) when I try to do it, everything will just fly apart like a clock. I'll have to see on my own whether it fits on the rod, since I imagine this is pretty variable from one tuba model to the next. But for disassembly and reassembly, are there tricks for managing the springs?

If the existing springs shouldn't be treated this way, can one order replacements with different tensions, so I can get the tension I want?

Thanks!

[Matt G]

How old are these springs?

[anotherjtm2]

How old are these springs?

About 20 years, I think. B&S/VMI.

Pull on the two ends of each spring - one-at-at-time - pulling on them about an additional 1/4 inch. This tightens while subtly unraveling, rather than adding turns - which would have crowded the spring boxes.
...

This sounds like what I would try with a piston spring. But maybe I can manage to straighten one turn on each fixed end (leaving one less turn on the rod), tighten one turn, then trim the excess.

[anotherjtm2]

If it sounds like what you would do with a piston spring, I don't believe I described the procedure clearly enough.

I've done (what I apparently failed to describe) countless times, and it works perfectly...UNLESS the (rotor levers') coil springs have already been pulled/trimmed like that too many times, and the spring coils are already fitting too snugly against the levers' hinge rods.

I think maybe the "subtly unraveling" part threw me, since pulling the end does tighten the wrap around the rod, though without adding any turns. Anyway, reading again while holding the horn and a pair of pliers, it makes more sense.

...also, I'm a person who (decades ago) thought that STRONG springs were the cat's pj's...and (now) understand that they're not always the best idea.
It might be advisable to (first) have the rotors and casings acid-cleaned, and see if their speed increases enough simply from the cleaning + spinning them back in with a lot of very thin oil. ...

Fortunately, the rotors are quite free, and they're as fast as I like when pushing the lever. On the return, they're free enough that they bounce. The effect is that they feel nice and light, but also a little sloppy.

So.... I tried your tip, and it might be just the thing; slightly tighter, not noticeably harder to push (still not as tightly sprung as the old Mirafone), but it feels more precise.

Thank you!

[Matt G]

is the bumper material in good order?

[anotherjtm2]

is the bumper material in good order?

Yep. Pretty good, anyway. It would have to be almost sticky to avoid the bounce with free rotors and weak springs.

[anotherjtm2]

My physics are flawed, here, but increased spring tension has a relationship to increased speed.

When a car bumps into a stiff object at a very low speed, it bounces back a little bit, but when a car hits a stiff object at an increased speed, it bounces back farther. The purpose of “crumple zones” in newer cars is to absorb much of the shock of hitting something stiff, to protect the passengers.

The thing that I would have suggested would have been some soft silicone bumpers on the returns… Perhaps even that gushy stuff that Jinboa has used, which - a bit like crumple zones, except over and over - is also effective in absorbing more of the shock of an impact.

Guessing that your bumpers are made of hard rubber, air – over time – hardens them…more like the consistency of wood, rather than with the pliability of rubber. This increases noise, as well as increasing bounce.

I’m not very smart, but I’ve messed with this a lot.

They're soft translucent silicone bumpers. I've seen hardened rubber, and this isn't that. Something that really absorbs the shock sounds interesting, though.

Tightening the springs has helped. Yes, that gives the rotor a little more energy to be reflected by the bumper, but it also raises the constant force pushing the rotor against the bumper, so it damps the bounces more quickly.