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Several of the piston valves my tubas whistle when going up and down. Not all the valves on the same horn but in this case
just 2 & 3 out of the 4. Speculation from one reputable tech is that the holes in the bottom and top of the actual piston are causing a whistle effect. Perhaps they are not calculated to be large enough. I don't know.
But why not then 1 & 4?
Are there any experts out there who have dealt with this and have found a remedy. I'm really not interested in more speculation but rather a solution. Do I need to have those breather holes drilled a bit larger? Or what?
I'm usually the one who can diagnose this type of thing, but I am at a loss.
That sound just won't go away and is becoming annoying.

Can they carry a tune?

This happened to me once on my old Miraphone 1291, and it drove me nuts... but it was a quick fix.

On the 1291, the valves are vented (small pressure-relieving holes on the side of the valve). The vent had become clogged with some horn-crud. A quick wash with some warm water, a little valve oil, and everything was good to go.

If your valves aren't vented on the sides, check the top or bottom holes to make sure there are no obstructions. Give them a good wash and poke around a little bit. Hope that helps.

I have been experiencing the same situation with my Wessex Bombino - all 4 valves whistling. Jonathan has had me try a lot of things, none of which worked. My local repair shop could not figure it out.

Here is what I have done which had no impact: ensured the path from piston bottom hole to top hole was clear; filed the valve guides so they did not encroach on the top vent hole; had the shop enlarge the opening in the top valve caps; tried different valve oils; experimented with the bottom water catcher on/off. None of this had any impact. (Jonathan is to send me 4 replacement pistons on his next China trip.)

Thinking that the whistling was caused by the air through the piston, I thought some reduction in air flow might help. I took a very small strip of paper the consistency of tissue paper (wrapping not toilet), rolled it into a thin strip and inserted into the bottom piston hole. Success! I did this with all 4 valves and the whistling stopped. I do keep check on them as the tip of the paper does stick out from the bottom piston hole. (Only a small strip is needed, so it is not a lot that sticks out.). I have noticed that this sticking out part becomes saturated with oil and adheres to the bottom of the piston - so no worry about it getting loose in the horn, which has not happened.
(I did try HVAC tape partially over the hole which worked, but it would eventually fall off.)

Hope this helps.

I had this problem on one of my valves. I was perplexed because cleaning didn't make the whistling go away. However, at a later time I cleaned the valves again and the whistling stopped.

I don't know what the problem was or how it was solved . . . all I can say is cleaning didn't work, and then later it did.

Hup

hup_d_dup wrote:I had this problem on one of my valves. I was perplexed because cleaning didn't make the whistling go away. However, at a later time I cleaned the valves again and the whistling stopped.

I don't know what the problem was or how it was solved . . . all I can say is cleaning didn't work, and then later it did.

Hup

You obviously scared the valve gnome away...

I had the whistling problem with the 3rd valve on my Yamaha 641 euph. The cause was the that the plastic valve guide was partially covering the top vent hole. Filing a notch in that guide cured the whistling.

I had this happening on my bmb. A chem clean resolved the issue. It is indeed caused by the top to bottom vent hole being obstructed.

I've had this a few times. Each instance was due to some kind of obstruction of the top or bottom vent holes in the piston.

First I would try to use a toothpick (or even paperclip, straightened) to clean out both holes. The I try to get water to run through. If the holes are visibly open, you might try some electronic parts cleaner in a spray can. Look for the kind that says it leaves no residue. They usually come with a long red tube to attach to the nozzle. You can insert the tube into the hole, spray, and work the angles as much as possible. You can blow/clean stuff out of the inside somethings by doing this.

But another factor could be the felt/cork on top of the piston (or anything else that sits on top, like some valve guide holders). I had a horn with pads that were too large and half-covered the top hole. So I just cut a flat spot on that side of the pad, and then made sure the flat spot was always what was sitting beside (not over) the hole.

Thanks so much for the responses. One that I tried was plugging up the whole in the bottom of the piston. Suddenly the whistling stoped and the valve was much quieter.
That makes me wonder if it works better when it is plugged, then why are there those top and bottom breather holes in the first place. Air can easily escape from the top around the valve stem or the bottom valve cap center hole.
I think I will try to find some rubber stoppers that fit or sand down a piece of cork.
I'll have to try it for a while. Something may rear its ugly head a little down the line.
I did plan on getting the valves vented eventually and perhaps that additional vent hole might alleviated the whistling.
But right now I am happy.
Thanks again for your suggestions.

PaulMaybery wrote:... That makes me wonder if it works better when it is plugged, then why are there those top and bottom breather holes in the first place. Air can easily escape from the top around the valve stem or the bottom valve cap center hole....

I've wondered about the same thing, Paul. I've seen quite a few pistons where there was no vent from top to bottom because the small passages around the cross ports are blocked with gunk, solder, etc. The fact that they are blocked doesn't seem to cause any problems as long as the holes in the casing caps are open.

I don't think those vent holes in the top and bottom of the pistons do much. However... there are stages through the construction, machining, and plating of a piston where they are important to avoid internal pressures due to heat.

Just a follow up. It appears that there are several causes of piston valve whistling on the down stroke. 1. air moving through the actualpiston. 2. Air escaping from the lower valve cap breather hole.

I did try reaming out the bottom valve cap to produce a funnel shape with the hole being wider at the outside. As it stood it could have been making a flute effect similar to the sharp edge of the fipple on a recorder or organ pipe.
The results of reaming were negative.

Then I took a lead from a post here and plugged the bottom hole in the piston by shoving a plug of neoprene "O" ring into the opening.
This cured the problem.

Other than what Dan mentioned that the holes may be there when the piston is soldered together to allow for the expansion of air, I see little purpose for them. The air does escape easily from the breather hole in the bottom valve cap on the down stroke, and by exiting around the valve stem on the up stroke.

Carefull observation showed that, in this case, it was the piston that was whistling, not the valve caps.

Thanks for all your help and suggestions.