Venting Valves, etc.

[windshieldbug]

"dad-dad"

[SplatterTone]

Pulling the slide for a "pop" should be no problem. But pushing it in too quickly could cause diesel ignition and explode the horn. Didn't the roadrunner trick Wile E. Coyote into doing this?

[Kevin Hendrick]

Pulling the slide for a "pop" should be no problem. But pushing it in too quickly could cause diesel ignition and explode the horn. Didn't the roadrunner trick Wile E. Coyote into doing this?

Sounds familiar:

"Dum ... da-dum, da-dum dum dum dum, dum dum dum dum BLAM!!"

("this accident could have been pre-vented"? )

[james]

Bill the "leaking" that can occur is usually when the valve is not pressed down fully. When the valves aren't vented, you can get away with not pushing a rotary valve down all the way(to an extent). Not so with the valves vented. If the valve is not fully pressed, you will hear a sound that I describe as "when your spit valve is broken off". Obviously this is because of air leaking out of the produced hole in the casing. I never hear this leak if the valve is fully down.

-James

[windshieldbug]

this accident could have been pre-vented?

Well, now that we're talking about it, maybe I should put a sign on my horn

"This tuba has been 258 days WITHOUT an explosion"

[MaryAnn]

Pulling the slide for a "pop" should be no problem. But pushing it in too quickly could cause diesel ignition and explode the horn.

yes! yes! yes! But you have to have diesel valve oil in it, and glow plugs to warm it up first in cold weather.

MA

[iiipopes]

And that might even be a good thing for those long Christmas parades!

[Kevin Hendrick]

Pulling the slide for a "pop" should be no problem. But pushing it in too quickly could cause diesel ignition and explode the horn.

yes! yes! yes! But you have to have diesel valve oil in it, and glow plugs to warm it up first in cold weather.

MA

And that might even be a good thing for those long Christmas parades!

Pursuant to all this, does anyone have a list of the cetane numbers for currently-available valve oils (should probably include various brands of lamp oil)?

[Bob Mosso]

Please educate me ... I'd becha that your valve integrity has been compromised.

Venting (if done correctly) does not create a leak.

When the valve is up, the unused slide is vented to the bottom of the piston. Try this, remove your #4 slide, play anything you want without using the 4th valve, everything should work fine. Venting the #4 is analogous.

When the valve is pressed, the vent hole is moved down and is completely covered by the cylinder (valve set) wall. The vent hole is approx 1/2 inch away from any port. It acts as if the vent isn't there (it has been moved to a spot where it can not function).

The only time it can have an effect is when the valve is partially pressed or in transition. When the valve is pressed just a little (1/4 of the full stroke), most of the air takes the short path, some of the air goes thru the slide, some of the air passing thu the slide will leak out the vent. If you press the valve to 3/4 of the stroke, the vent will be covered by the cylinder wall and has no effect.

Okay it does cause a _transitional_ leak. I considered this in detail before I drilled. If the vent is drilled in the center of the port it doesn't get covered until 1/2 stroke. I drilled my vents low on the piston so that they get covered by approx 1/4 stroke. I also decided to use the smallest possible drill bit, 1/16 inch. A smaller hole takes less valve stroke to cover it.

Put this possible tiny transitional leak in perspective. How fast do you press and release valves? How much air will leak out durring normal valve transitions? Do you ever have the need to slowly press a valve while playing? I've proven (at least to myself) that the advantages of venting are very significant and I am unable to feel or hear any disadvantages.