Venting Valves, etc.

[Bove]

You can vent the valves on rotary valves as well as pistons.

The previous poster’s PT-6P should be a piston valve tuba.

One thing to note on this subject is that there sometimes may be disadvantages to venting valves... I can’t remember now exactly what these might be, but I know that having this done to your tuba is not always a “no-brainer.â€

[Roger Lewis]

Hey LV
Where you at?
Ratboy

[docpugh]

How much can one expecto to pay to have the valves vented? Should you vent all the valves?

[Rick Denney]

How much can one expecto to pay to have the valves vented? Should you vent all the valves?

It's not expensive at all with pistons. I paid less than $50. The cost of one is over half the cost of all four, so you might as well do them all.

Venting rotors requires drilling a small hole in just the right spot on the valve casing. It's not difficult, but it requires disassembly of the valves to clean out the shavings. I suspect it costs a bit more.

Rick "who observed a noticeably improvement on the York Master, but who has not vented the valves on the Holton (yet)" Denney

[Allen]

I had my first valve vented on my rotary tuba. Also, I had the corresponding valve slide lapped so it moves very easily. The first valve slide is the only one I move while playing. I'm pleased with the results. I didn't notice any difference in sluring.

One disadvantage of having valves vented is that it makes it difficult to check the tightness of the valves by pulling a slide, then operating the valve while listening for a pop. You'll never get a pop from a vented valve.

Allen Walker

[Matt Walters]

Like Allen said, you'll no longer be able to hear a "pop" when you move the slide and then push the valve. To some people, that seems to be very important. As for me, I don't need the sound of a "pop" to tell me if a horn plays well. It plays well or doesn't.

Venting rotor valves is cheapest when combined with a scheduled Chem clean and service. I'm already taking the horn apart and cleaning it out. I don't charge double labor on that, just the time to drill the holes and deburr them. That's only an extra half hour labor that way.

[Bob Mosso]

... Matt Walters mentioned that he thought that venting valves made a bigger difference. ... I must say that venting does make a big difference in slurring.

I'm a bit of a home machinist and decided to vent the valves on my euph. I concur with LV, there are advantages/improvements other than eliminating popping. I noticed quieter valve action and easier slurring.

Any comments on hole size and location? I drilled 1/16 inch holes low on the piston (but still within the port area). With the low positioned vent as soon as you start pressing the piston the vent gets covered. If the vent was high on the piston it wouldn't be covered until the piston is fully depressed. What difference would/could this make?

[Tubadork]

Hey,
What is the down side of having your valves vented? (If any) I've heard that it's not so good to have rotars done because it is like causing a leak in the horn. I have no idea if this is right or wrong, just trying to clear up what I've heard.
Cool,
thanks,
Bill

[windshieldbug]

Hey,
What is the down side of having your valves vented? (If any) I've heard that it's not so good to have rotars done because it is like causing a leak in the horn. I have no idea if this is right or wrong, just trying to clear up what I've heard.

My Mirafone 184 CAME with vented valves, I've had other rotary horns vented and it has never caused any downside that I could notice. The valve change is usually so fast that I doubt that the air column is open for any appreciable time. I have never tried to "half valve" such a horn, but if it were required, I'm sure a 1/4 valve would work just as well for whatever effect you were trying to achieve and not leave the vent open. In point of fact, when pulling or pushing a slide, it happens so quickly that often moving a rotary valve and using the slide happen simultaneously. It's when you do it before that you have a "pop". And, to the person that tests valves that way (which I wouldn't recommend, because it only hastens the eventual leakage problem, even if just by an iota) all one has to do is cover the vent with one's finger!

[windshieldbug]

[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.