Valve problems

[Chuck(G)]

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.

[windshieldbug]

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.

[Rick Denney]

...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

[Bob Mosso]

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

[Chuck(G)]

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?

[windshieldbug]

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?

[Chuck(G)]

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.

[Chuck(G)]

Susceptible to corrosion or not - do the aluminium alloy horn sound differently from brass horns? Or is it within normal variance?

Check out the link above the photo--the response seemed to be very positive.

[Kevin Hendrick]

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

That's a very interesting design -- it'd be worth trying!

... years of experience with metal constructs and corrosion clearly shows that thin aluminum tubing is an appalling choice for instrument tubing- especially in a dank setting such as the interior of a french horn.

I suspect stainless steel and/or titanium would be better choices ...