Seeking clarification about venting a piston valve

[Tubajug]

So I spent some time yesterday reading old posts about venting a piston valve and I want to make sure I understand things correctly. I'm a more visual learner when it comes to things like this, so I put together a crude photo below to see if I understand.

If I understand the process, the red circle I drew on the piston lines up with the red circle around the first valve slide port when the piston is in the "up" position. The hole would then be drilled in the piston where I put the blue dot, correct?

There are several competent repair techs here in town, but all are mostly just school repair techs, and thus haven't done much "tuba specific" stuff like I've read about on here and wanted done. The tech I use is very open to trying all the projects I bring to him and letting me help out, so I like that. I spoke with him last night and he said that if I bring some instructions and/or pictures on how to do the venting, he's willing to help me.

So please correct me if the photo I made up is incorrect or feel free to add your own photos of your work venting pistons if you have them so I can make sure we do this correctly. Thanks!

[luke_hollis]

The idea is simple. The valve is hollow on the inside except where the tube goes through join 2 different sides of the tubing (in and out).

The purpose of venting is so you can pull the slides when the valves not depressed without creating suction. When the valves are depressed, there is an open pathway of air you would be blowing through and hence no pop.

You need to measure to find the place to drill a small hole no deeper the thickness of the valve wall that will create an opening passage to the bottom of the valve for air to pass when you push/pull with the valve in a non-depressed position. You also need to make sure you don't drill through any tubing that may be snacking through the valve at that point.

If go to the repair shop and the repairman doesn't know what you are talking about, go somewhere else.

[Dan Schultz]

Before you go any further... make sure the factory vent through the piston from the hole in the top cap to the hole in the bottom spring plate is clear. I've seen quite a few pistons that have been clogged with solder and such straight from the factory.

It's difficult to tell if you are in the right spot from the picture you posted.

When you do decide where to drill... use a drill press with a stop on it so you just go through the piston outer sleeve.

[Art Hovey]

Yes, your photo indicates that you have the right idea. Drilling there will do no harm so long as you penetrate only the outer shell of the piston. It is important to smooth off the edges of the hole after drilling so there is no "burr" left to interfere with smooth motion of the piston. It's not difficult. I have done it with a hand drill, but it's easier with a drill press. It helps to start the hole with a dremel tool, but that's not absolutely necessary so long as the drill bit is sharp. On one of my tubas I found that some sludge had accumulated inside the piston (after about 12 years of use) interfering with air flow through the vent holes. I was able to clean it out with my water-pik.

[Tubajug]

Thanks for all the responses so far everyone. Now I need a little clarification about another issue that has come up.

Several of you have mentioned only drilling through the outer wall of the piston. Are pistons double-walled or are you simply saying "don't drill in one side and out the other?" I've always thought they were simply a single layer, hollow tube. Is this not correct? If anyone has a "cut-away" drawing of a piston or something similar to share (again, I'm more of a visual guy) that would help me out tremendously. Thanks again for the help.

[Dan Schultz]

Thanks for all the responses so far everyone. Now I need a little clarification about another issue that has come up.

Several of you have mentioned only drilling through the outer wall of the piston. Are pistons double-walled or are you simply saying "don't drill in one side and out the other?" I've always thought they were simply a single layer, hollow tube. Is this not correct? If anyone has a "cut-away" drawing of a piston or something similar to share (again, I'm more of a visual guy) that would help me out tremendously. Thanks again for the help.

The outer sleeve of the piston is a single layer of material. What folks are telling you to avoid is running the drill in too deep and penetrating one of the cross-ports. Sometimes those ports are VERY close to the outer sleeve. I like to actually set a collar stop on the drill itself. Something else you can do is slip a piece of brass tubing over the drill so only about 3/32" of the drill tip is exposed.

I've also seen the area inside the area that's supposed to be hollow filled with solder. There are a few things that can cause trouble so I like the idea of a stop over the drill rather than to go by 'feel'.

[MartyNeilan]

I picked up a set of MW pistons that had at least one vent hole drilled in the wrong place. I filled it with Marine JBWeld. A year later, it seems to be holding up.

[Tubajug]

Thanks again for all your replies. I feel like I've got a good grasp of it now. Happy Holidays!