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Are you trying to see if you need to add Rislone to your valve oil? Compression numbers are nice, but they can be misleading. Assuming the valves and casings are not out of round, they can function with thick valve oil and a larger gap than most other instruments. The best way to tell is when you can't keep your tone centered with Hetman's oil for older horns, then it's time for a valve job.

Hey, bloke --

From doing compression testing on my E-type convertible after I bought it to see if I needed to to do any work on the head, valves, gasket or rings, I believe the number has to do with the proportion of how much pressure the valve actually holds compared to the pressure the valve theoretically can hold. As you and I both know, this is a spurious measurement when applied to brass instruments, because, unlike an automobile engine, the valves aren't designed necessarily to hold pressure, but simply to redirect the airflow, which, at the very low pressure the human lungs can exert, is simply an insignificant figure until the valves are so worn that nothing holds. I don't know about how you determine if an instrument needs a new valve job, but for me, so long as the valve slides "pop," even a little bit, there is still enough sealing of the bores with the proper application of valve oil that there is nothing to worry about.

Supposedly, the German WWII debate was that, as they were carrying on parallel experiments with nuclear weapons, they were overly concerned with purity of nuclear fuel, while the USA was concerned about the practicality of just getting it usable first. So it's no suprise to me that the horn on which this measurement was taken is a M-W. And as you observed in your post, since valves 1 & 2 are used so much more often than 4, it sounds to me like BostonDomer has a fine tuba that should serve him well for the rest if his life, his childrens' lives and anyone else who cares to play it some generations from now.

iiipopes wrote:Supposedly, the German WWII debate was that, as they were carrying on parallel experiments with nuclear weapons, they were overly concerned with purity of nuclear fuel, while the USA was concerned about the practicality of just getting it usable first. .

OT, but interesting...

As far as the WWII German nuclear war effort was concerned, they weren't all that serious about nuclear weapons. They essentially went through the same assessment that the US did, but came out with a different conclusion.

The US concluded that the war was likely to be long and the Manhattan project to be very costly, but would eventually produce a usable weapon. The Germans made the same assessment, but dropped serious military research because they realized to prevail, they needed a successful conclusion to a short war--they just didn't have a long enough bench for a long-haul slugout.

Recently, using Nazi records and a barrel of heavy water recovered from the sunken freighter Hydro, it's been established that the Nazis produced less than a half-ton of heavy water--far less than required to build a reactor capable of producing weapons-grade plutonium. Most of the German nuclear research was performed in secret civilian labs.

Hey Chuck(G) -- thanks for the post. I really did think the Nazis had developed their nuclear program further than that, but got hung up on purity of fuel. Bad metaphor on my part, trying to find something to illustrate the difference between the theory of numbers verses the practicality and reality of actually playing the horn.

compression tester

iiipopes wrote:...the valves aren't designed necessarily to hold pressure, but simply to redirect the airflow, which, at the very low pressure the human lungs can exert, is simply an insignificant figure until the valves are so worn that nothing holds....

The pressures held by the valve are dynamic and in the frequency domain, rather than static as is the case in a car engine. We already do leak-down tests by pulling slides and popping valves, and these tell us if the valve will hold pressure over a matter of a second or longer, which is much more than long enough to accommodate the pressure fronts in acoustic sound. But it may not model the magnitude of the pressure front adequately. Those tests are usually calibrated by experience, though. I might have experience with tubas that had debilitating valve leaks, and I might have built a little database in my mind of how those instruments fared when pulling slides and popping valves, for example. Not precise, of course, but maybe accurate enough for a quick check.

A leak-down test, on the other hand, will tell us how much air gets past the seals of a given system. The leakage is compared to the air being supplied. That is a completely static test that may fail completely on a tuba that plays just fine. It is far more precise than it is accurate, because it does not measure sealing in the frequency domain where it counts. As with cars, it does more to tell an owner to worry about something that he wasn't worried about before than to identify any real issue.

All that is just a fancy way of agreeing with both you and Bloke.

Rick "not even all that impressed with leak-down tests on car engines" Denney

Thanks.

bloke wrote: My understanding is that the goal of piston-casing or rotor-casing tolerances on top-grade brand-new instruments is .001" difference...

...My Buescher C helicon pistons-to-casings fit is somewhere in this neighborhood, and (by gawd) I'd BETTER NOT have ANY dirt in the valves and they HAD BETTER be OILED and completely free of *new "un-rubbed" casing oxidation.

...with far less difference than that (due to the small diameter of these parts) on the spindle bearing parts of rotors.

Perhaps more slop than this is acceptable on large tuba pistons and large tuba rotors than small trumpet pistons and small French horn rotors.

For instance, when I've asked Dave Secrist to rebuild "short-action" sousaphone pistons/casings, his typical "amazing" tolerances simply don't work (at least not for me).

I end up going back and making 20K pistons/casings fit "sloppier" than as received from Dave. The problem with those huge "short-action" pistons is that there is so much SURFACE AREA that the FRICTION slows the pistons down below acceptable speeds. That is the main reason why trombone slides have at least .002" of space all the way around (.004" difference, typically) between the inside playing slide tubes and the outside playing slide tubes.
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*and, if I haven't played any gigs on that instrument in more than a week's time, I have to oil and "work" the valves for 1-3 minutes before they are "perfect" again...but boy are they PERFECT once I rub down any newly-formed oxidation!

' no brag. ' just fact.

And to add to that, if you use oil that is too thick, part of the problem with being slow is not just the tight tolerances, but the pushing of the valve against the viscosity and surface tension of the oil and any condensed water as well. Same reason, before multi grade oils, autos required 10 or 20 weight in the winter and 20 to 30 weight in the summer, and 50 weight in Arizona. I'm not saying to get a bottle of Hetmans #1 and #2 and mix them proportionally for the horn or the playing temperature outdoors, as that would be rather retentive, rather to not worry about it. If you don't have to oil too often, and the slides pop when you pull them, enjoy the horn!