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That remark

If I leave the tuba for a while to cool down, they’re fine again.

is very suggestive, and one might think that your problem may be related to the expansion of a material at rising temperatures. However, the corresponding coefficient is REAL small, and so is the rise in temperature of your horn´s valves.

The tiny amount of expansion (and deformation) just may be enough to change the valve´s exact position in the casing.
The best I can come up with is to get it to a repairshop and have them look over the valves.

I once fell on my tuba, and in addition to a dent there was a stuck valve (that is, it worked unreliably, wasn´t permanently stuck). Melton just lapped it in and gave it a thorough clean job.

PÃ¥l Magne Austnes wrote:Seems like some kind of plastic material in the rotors, but enclosed by metal.. I've sent an e-mail to Hirsbrunner with questions!

Thanks for the tip!

BTW: the instrument is probably at least 20-25 years old, probably more..

This is the source of your problem. Hirsbrunner used metal encased nylon rotors on their tubas for a time. It allowed for light and fast action, but they were notorious for seizing up when they heated up. It had to do with the difference in coefficient of expansion of plastic vs. metal. The best solution is to replace the rotors with metal ones. Hirsbrunner should be able to help you with this. I don't know if they were doing this gratis at any time, but it certainly seems like they should replace them because it was a design flaw.

"Gratis" is used in English too. It's root is Latin.

Latin: gratiis (This form of gratia is also the source of the English term.)

Deutsch: gratis

English: gratis, free

I have a similar problem with my valves as well. Hirsbrunner will NOT send replacement valves for free, I have already asked. I think its was somewhere around $300-$400 (US) when I asked last year. His solution was to just lap the valves in the casing, but I have not done this yet.

I'm a little hesitant about doing this as it will take away some of the metal to make room for the expansion. Well, what happens when the valves are cool? Does it leak? I dunno. The only "good" solution is to replace the valves, which will cost some $$$. First you have to buy the valves. Then you must find someone very skilled to actually "fit" them into the tuba, as the valves are just a "rough" size, and needed to be trimmed up a bit to fit nicely in the valve casing. Each valve case is slightly different, owing to how it has aged over the years.

Hope this helps. There are a few of us on the board that have discussed this before with each other. Let me know how it turns out.

Pal, do you do any orchestral playing and if so, how often do you use your yamaha f versus the BBb? What do your fellow brass players think of your yamaha versus traditional rotary valve f's?

Interesting. So you lap them in at their highest rate of expansion. What then? Do you install a heater on the valve cluster? If you lap them in when they're hot, won't that reduce the amount of friction when they're cold, thus making them stay cold? I don't know-it seems to me that it would be better to try to keep them cold and unexpanded, rather than setting them so that they work best when hot. I'd also think that the hotter they get, the bigger they'll get, so that solution seems problematic. Will Hirsbrunner sell you new all-metal rotors? It seems like if you're going to go to the trouble of lapping them in, you might as well lap in something that's going to work. If you lap in the bad rotors, you'll be grinding away at the insides of the casings as well as the outer diameter of the rotors, and you might not be able to get it to work if you decide to use all-metal rotors in the future.

If you do follow the factory recommended "fix," while you're ordering the lapping compound from Hetmans, order some of their thicker rotor oil to go with it, as you will need it with having increased the rotor/casing gap.

It makes sense to lap the rotors at playing temperature or slightly above, since that's where the horn will be used. Of course, you must be sure to do a longer, literal "warm-up" of the instrument before playing it in concert from now on so your intonation and tuning don't change half-way into the first piece.

And, of course, GO SLOWLY! It is always better to lap a little, reassemble, find a little stickiness is still there, and repeat the entire process, even though it may take a few extra hours, than to lap too much and ruin the rotor or the casing.

Then, start saving your money for a new set of rotors and the shipping to get it done at the factory, as you WILL need it eventually. This is as true of the rotors as any machine part that moves against another, whether tubas, automobiles or factory machinery, especially when you have dissimilar alloys or other materials with variant rates of thermal expansion coefficients. That's why I'm having problems, from a philosophical point of view, of accepting stainless steel as a valve material instead of traditional monel for pistons and the various brass or bronze alloys, depending on the instrument, for rotaries.

That's why I'm having problems, from a philosophical point of view, of accepting stainless steel as a valve material instead of traditional monel for pistons and the various brass or bronze alloys, depending on the instrument, for rotaries.[/quote]
iiipopes, could you elaborate a bit?

do brass and stainless really expand that much in conditions that are comfortable for humans?and at noticeably different rates?

TheEngineer wrote: Brass tends to be more malleable, softer, and less inclined to gain/shed heat. Stainless Steel tends to be a harder metal that gladly gains/loses heat.

I'm a little confused over the "gains/loses heat" terminology. What physical characteristic are you referring to? Thermal conductivity? Specific heat?

I'm having trouble understanding.

FWIW, titanium rotors in platinum casings should make a good combination, if expense is no object.

TheEngineer wrote:I think what he's getting at is that because the material properties of the two metals are so dissimilar. Brass tends to be more malleable, softer, and less inclined to gain/shed heat. Stainless Steel tends to be a harder metal that gladly gains/loses heat. Because of these differences the two would, in theory, not be good materials to have next to each other in a system where there is heat and friction (like, I don't know, valves). If the brass expands more than the stainless then you don't have a good seal once you warm up, if the stainless expands more you get binding.

You are suggesting that because stainless steel gains heat faster than brass, it might expand quicker, even though both have similar coefficients of thermal expansion. The coefficient of thermal expansion for brass is between 10 and 11 micro-inches/inch-degree-F. Stainless steel varies, but typical values range from 6-10. So, under steady-state thermal conditions, a stainless valve might be a hair loose in a brass casing, though I doubt the difference would be easy to measure.

But (and there's always a but) brass conducts heat faster than stainless, by a factor of about 5 to 1. So, the casing will expand a bit faster than the piston.

Malleability and other working characteristics don't enter into it. We hope that thermal effects are not sufficient to cause the material to yield mechanically, which those other characteristics describe.

I surveyed a couple of plastics just to get a feel for the numbers, and given that I don't know what polymer Hirsbrunner used in those old valves. The nylon and polycarbonate that I looked at had coefficients of thermal expansion varying widely in the range of 20-70 micro-inches/inch-degree-F. That's 2 to 7 times that of brass and stainless steel. Thus, the diameter of the rotor might change by as much as .010" over the 80-degree range that a tuba player might face (from freezing to outdoors in Las Vegas during August). That's enough to cause a problem, it seems to me.

The coefficient of thermal conductivity of plastics seem to be perhaps 1% of stainless steel and 0.2% of brass. Thus, the Hirsbrunner valves probably take a while to start causing problems in a high-heat situation because they insulate themselves effectively. It also tells me that if you heat them up in a pan of warmish water (like what comes out of the hot tap) for 15 or 20 minutes, they'll probably stay hot enough during lapping to have the desired effect.

Rick "thinking there's a reason those fancy stainless pots and pans have copper on the bottoms" Denney

So it's thermal conductivity that's worrisome? I had no idea that extreme temperature differentials (on the order of more than a few degrees) existed inside of most tubas. Is this really true? I'dve thought that temperature differentials between parts that are in contact (or nearly so) wouldn't be more than a few degrees, tops.

Chuck(G) wrote:So it's thermal conductivity that's worrisome? I had no idea that extreme temperature differentials (on the order of more than a few degrees) existed inside of most tubas. Is this really true? I'dve thought that temperature differentials between parts that are in contact (or nearly so) wouldn't be more than a few degrees, tops.

The thermal differential is not between the valve and the casing, but between the temperature of the parts when they were constructed, finished and assembled and when they are used as you play the instrument. The tolerances between the two surfaces were set at say "room temperature" of 72 degrees, but the performance temperature sitting in the sun in Las Vegas is 105 degrees. While both the valve and the casing are now at 105 degrees, the casing expanded at one rate while the valve expanded at another changing the gap (tolerance) between the surfaces. The same would apply if the performace temperature were 40 degrees except we would be referring to the contraction of the parts instead of the expansion. I hope this explanation helps...

Bandmaster wrote:The thermal differential is not between the valve and the casing, but between the temperature of the parts when they were constructed, finished and assembled and when they are used as you play the instrument. The tolerances between the two surfaces were set at say "room temperature" of 72 degrees, but the performance temperature sitting in the sun in Las Vegas is 105 degrees. While both the valve and the casing are now at 105 degrees, the casing expanded at one rate while the valve expanded at another changing the gap (tolerance) between the surfaces. The same would apply if the performace temperature were 40 degrees except we would be referring to the contraction of the parts instead of the expansion. I hope this explanation helps...

I understand that part--I believe it's called "differences in the coefficient of thermal expansion", but I'm still trying to understand the bit about "gains or loses heat quickly" and why that would have a substantive effect on operation.

Chuck(G) wrote:I'm still trying to understand the bit about "gains or loses heat quickly" and why that would have a substantive effect on operation

Like a cat, if your tuba is in heat it can attract many unwanted strays, all loudly bellowing and blatting, making it very difficult for you to be heard.

Chuck(G) wrote:...but I'm still trying to understand the bit about "gains or loses heat quickly" and why that would have a substantive effect on operation.

It wouldn't, which I suppose you knew already.

As my numbers showed, the plastic material is a good insulator and changes temperature slowly. So, if you heat up the instrument suddenly by taking iit out into the sun, the casing will warm up quite a bit faster than the plastic valve. It could take a few minutes for the valve to catch up.

Maybe then if you move back into the walk-in refrigerator for another performance after playing out in the sun, the casing might shrink more quickly than the valve by enough to cause a problem.

The problem is a steady-state problem of thermal expansion. When playing conditions are warmer than construction conditions, it will take a little while for the valve to catch up to the casing, delaying the effect of too much explansion. How much? I dunno, and I don't think it's relevant.

Even though I don't think it's important, I don't think I agree that both parts will be only a few degree apart if the instrument is moved to a suddenly hotter condition, particularly if bright sun is involved. They will get there eventually.

The main point of my previous response was to calm anybody's fears that stainless steel valves are dissimilar enough from brass casings to ever cause a problem solely based on thermal behavior. The problem with the plastic valves is documented, and the numbers bear it out. Whether the valves start to stick immediately or in five or ten minutes doesn't seem as relevant to me.

Rick "who suspects Chuck knows more than any of us about this stuff" Denney

Chuck(G) wrote:but I'm still trying to understand the bit about "gains or loses heat quickly" and why that would have a substantive effect on operation.:?

I think what is trying to be said:

If one of the parts has a higher thermal mass it will take more heat to raise it to be at the same temperature as the other part.

And, if one of the parts has a lower thermal conductivity it will resist absorbing the heat, thus taking it longer to be at the same temperature as the other part.

Both of these conditions could cause thermal gradients, which could cause parts of similar materials to expand differently.

I personally don't believe thermal gradients, thermal mass, or thermal conductivity has any significant effect. Its all about thermal expansion.

Bob

Bob Mosso wrote:If one of the parts has a higher thermal mass it will take more heat to raise it to be at the same temperature as the other part.

Okay I'm being argumentative.

When I take a tuba into a warmer room from a cooler one, the source/sink of heat is essentially (as regards the tuba) infiinite; e.g., taking a cold tuba into a warm room is not going to cause the room to cool off noticeably.

All of which is my way of saying that it's the coefficient of thermal expansion that's going to have the single largest (and, to my mind, the only significant) effect on the warm or cold performance of valves.

There are other factors in material choice. For a really forward-thinking approach, consider the Mark Veneklasen horn:

http://www.hornplayer.net/vhorn.asp

Aluminum alloy tubing and valves, rubber o-ring sealed joints, streamlined bends--a real marvel. that could be completely disassembled without soldering. There were some problems with the anodized aluminum valves, but some think it was because of faulty manufacturing.



So, who'd like to do a tuba along the same lines?

Chuck(G) wrote:There were some problems with the anodized aluminum valves, but some think it was because of faulty manufacturing. So, who'd like to do a tuba along the same lines?

What? Build one with faulty manufacuring?

windshieldbug wrote:

Chuck(G) wrote:There were some problems with the anodized aluminum valves, but some think it was because of faulty manufacturing. So, who'd like to do a tuba along the same lines?

What? Build one with faulty manufacuring?

Well, it turns out that the crud that was slowing the valves down was a mixture of anhydrous lanolin and saliva with some sort of wildlife inhabiting it. It seems that brass does have some other useful properties than the obvious ones.