What is the function of the hole on top of the pistons?

[euphomate]

I recently took possession of a new cloned Eb compensating tuba made at the Jin Bao facory in China. All seems good with the horn, and I'm quite impressed with the build quality so far. Except for one thing. The small hole that is always drilled into the top of pistons (valves) next to the nylon valve guide is missing on the smaller fourth valve piston. All the others are in place, as are the holes in the bottom of all of the valves. What is the function of the top hole drilled into tuba pistons? Does it matter if the drilling of that hole in the fourth valve was some how forgotten? The valve functions just fine as it is, no sticking or other issues. I have asked around in my music environments, but nobody seems to know the answer. Advice please.

[Matt G]

It allows air to pass through the interior of the valve so that you don’t get a pressure differential in fast playing (sluggish valves).

[euphomate]

That makes sense. Fortunately, my limited talents do not require fast fingering on the fourth valve. I will wait and see what problems might show up, and if necessary take a visit to my tech (Covid travel restrictions permitting).

[GC]

Some people use those as ports to oil their valves with a needle oiler. Keeps from having to undo the valve caps.

[Alex C]

Some people use those as ports to oil their valves with a needle oiler. Keeps from having to undo the valve caps.

That wouldn't supply oil to the valve in any effective way.

[MikeMason]

I think GC is referring to the holes bloke drilled in the top of his top valve caps allowing oil to be dropped on the side wall of the actual piston. Different from the vent hole in actual top of valve.

[GC]

Yes. Thank you, Mike.

[Daniel C. Oberloh]

We typically use it for tooling engagement as power transmission point during the honing and grinding of the piston.


Daniel C. Oberloh
Oberloh Woodwind and Brass Works
http://www.oberloh.com" target="_blank