Valve inspection with borescope

[AndrewMeronek]

Lately I've noticed on my bass trombone (the Getzen that had the valve lever break off) it seemed like something is very occasionally wanky with something stuck inside it. I snaked it out to be sure and have verified that this is not actually the case. So, I am now wondering if there is still something wrong with the valve.

I also just recently bought myself a borescope, so I put it to use. A picture of the valve when open:

20240824_103644.jpg

and partially closed for context:

20240824_104001.jpg

This got me to wondering, why does it look like the ID of the valve mechanism itself seems to be larger than the ID of the valve casing?

That asked, I suspect that the valve may not always be opening all the way.

Yes, I probably should set the date/time on my borescope.

[greenbean]

That's funky looking. Is it just the core has moved past the point where it should stop?...

The second phots shows the core moving well past the point where it should stop. Yes? ...

[AndrewMeronek]

That's funky looking. Is it just the core has moved past the point where it should stop?...

The second phots shows the core moving well past the point where it should stop. Yes? ...

Honestly, I don't know what a "non-funky" looking rotary valve should look like from inside.

The second photo is the valve roughly half-closed; definitely not too far, at least by the way the valve lever action works.

Also: because of the tubing and the shape of my borescope, I can't get a good image of the 2nd (dependent) valve.

[greenbean]

Well, you should be able to see clearly the edge of the rotor port and where it stops - either short, just right, or too far. Perhaps new bumpers are in order?

[AndrewMeronek]

The bumpers are fine.

Does anyone else have a borescope and a rotary valve who can post pictures of a "correct" action?

I'm going to take the horn in to a local music shop next week, but it'll be nice to give them as direct a cause of what's funky as I can.

[2bobone]

Andrew : I started that borescope thread about 7 years ago and am really impressed at how many players are relying on the images that solve one of the most perplexing problems of valve alignment. I've attached what I look for as a great image of alignment [Butler C12 - Instrument Innovations valve]. I hope it is useful.

[Sesquitone]

This got me to wondering, why does it look like the ID of the valve mechanism itself seems to be larger than the ID of the valve casing?
That asked, I suspect that the valve may not always be opening all the way.

Do your valves have RELIABLE witness marks? And are they lining up very precisely?

[AndrewMeronek]

Andrew : I started that borescope thread about 7 years ago and am really impressed at how many players are relying on the images that solve one of the most perplexing problems of valve alignment. I've attached what I look for as a great image of alignment [Butler C12 - Instrument Innovations valve]. I hope it is useful.

I think it is. That shows what I would assume, that the ID of the valve matches the ID of the valve casing apertures where they meet.

[AndrewMeronek]

Do your valves have RELIABLE witness marks? And are they lining up very precisely?

I don't know about the witness marks, but I think it's clear that it is NOT lining up properly.

[2bobone]

I can't honestly say that I've ever owned a horn with reliable witness marks on the valves save one --- a cheap JinBao bass that I bought on a whim. In my early days I took those marks as gospel and trusted them simply because that is what you did, having no alternatives. The borescope had only been invented in 1960. I had a student at the time who would experimentally place small pieces of cellophane from a cigarette pack between the bumper and the valve stop. A different number of pieces would actually make a difference in horn response. Being able to actually see the problem was a boon to valve players everywhere. Let's hear it for the borescope and technological advancements !!

[brassmedic]

valve.jpg

Am I the only one who has no idea what we're looking at? Are we looking through the knuckle at the rotor? Why is the opening in the casing oval-shaped? And what is the second smaller concentric ring beyond the rotor? And what on earth is that little blob near the center of the photo? Did you get an M&M stuck in your valve?

[OneTon]

Am I the only one who has no idea what we're looking at?

I can’t tell what I am looking at either.

[Sesquitone]

Imagine that you are a sound wave travelling through a brass instrument, starting off at the mouthpiece. Ideally, you (along with the full set of all of your beautiful harmonics) would like to travel all the way through without any interruption of any kind until you reach the open end and then reflect back (with a change in phase) to the "closed" end, and so on. If you are travelling through a trombone, you will "put up with" some small premature reflections of part of your energy from the tiny discontinuities in bore size between the inner and outer slides (and again in any tuning slide). But you really shouldn't need to put up with any other discontinuities anywhere else! Especially in the slide receiver (a common culprit) or any valves along the way. [And, ideally, not at the end of the mouthpiece shank (of arbitrary wall thickness). Unless you are travelling through a trumpet!]

According to the pictures shown by the scope, there are some "nasty" discontinuities between the valve knuckle and the rotor channel. [Not to mention what looks like a solder blob.] These will sap a lot of your energy and cause major unwanted reflections that can distort your overtone series (i.e. tone quality)—and possibly turn you into a "wolf tone"!

Even a tiny misalignment between the rotor channels (or ducts) and the casing ports and knuckles can cause distortions of this kind. You don't have to have "loss-of-seal" before tone quality suffers.

Bumper-stop alignment is critical. Razor trimming of fixed stops is tricky and frustrating (especially when you trim too far and have to start over!); and not always accurate. That's why I am a strong advocate of individually adjustable stops, as shown in the picture below. By first lightly snugging the set screws and carefully adjusting the individual arms—backing off, if necessary (which is not possible with razor trimming)—you can align precisely, then tighten appropriately. This happens to be what we use with the CAIDEX valve; but something similar (with the necessary surrounding guard-ring to avoid loosening) could be used with any type of rotary valve (or other geometries).


.

[Sesquitone]

Here's another trick. First, withdraw the bumper material. For a single valve or the "upstream" valve of a dependent geometry, you may be able to snake through a damp cloth of slowly increasing width (from the slide receiver to the open gooseneck) until it won't go any further and the valve cannot be moved. This, of course, is the correct orientation for the unactivated position. You can now insert the bumper material for that stop—while razor trimming exactly. If there's a visible tick on the end of the spindle, you can see if this lines up with any witness mark on the casing. If not, perhaps you can place a very narrow mark on both components (with a very fine felt tip)—you probably don't want try to make scratches in the metal! Withdraw the cloth, then rotate the valve exactly 90º. This is tricky to measure, but you might be able to mock-up something with a protractor. You may be able to freeze it in this orientation using appropriate rubber bands, &c. Now you can insert and trim the other bumper material. You might be able to do this for a second valve with inline geometry. Probably not with dependent geometry.

[ghmerrill]

My experience with borescopes is that it's very difficult to tell what you're seeing unless you have a lot of experience with borescopes -- and in fact with using borescopes for the specific environment in question. I've had great benefit from using them on black powder rifle barrels (once I figured out how the weird image was actually showing me something), HVAC ducts (same story on interpreting the image), and seeing into my crawlspace through a vent (not so many problems with the image). But there are issues of distortion, focus, field of view, light reflection, and perspective ("So which way is up?") that abound. Almost anything seen through a borescopes will look odd until you've got some experience in interpreting it.

I've found that I don't use them on my valved instruments because either I can pretty easily see (especially on the trombone) what I want to with just a flashlight; or (in the case of tuba and euphonium) I can't get the camera to go around the tight bends that I really need it to. Also, the trombone valves are so easy to take apart that scoping them as a preliminary isn't all that useful -- unless you think that disassembling the valve might damage it because of something caught in it.

Also, my own impression is that if you really want to get something reliable from a borescope, you'd better be willing to pay for it -- say about $500 and up. Anything up to that point seems to be more "hobbyist" level: handy and often crudely useful, but not beyond that. You at least need one with an articulating head and a better camera and lighting than you get on the cheaper ones. What I have now is a DEPSTECH 5.5mm scope that cost me about $50 and it's "adequate" for most of my needs, if somewhat irritating. However, a lot better than those $10-$25 jobs.

[AndrewMeronek]

Am I the only one who has no idea what we're looking at? Are we looking through the knuckle at the rotor? Why is the opening in the casing oval-shaped?

It took me a bit to figure out what I was looking at too. Yes, and probably because of the angle.

And what is the second smaller concentric ring beyond the rotor?

I think that is the boundary between the valve casing and the brass tube it connects to which is going away from the camera in that perspective.

And what on earth is that little blob near the center of the photo? Did you get an M&M stuck in your valve?

The blob is a droplet of water.

[brassmedic]

Am I the only one who has no idea what we're looking at? Are we looking through the knuckle at the rotor? Why is the opening in the casing oval-shaped?

It took me a bit to figure out what I was looking at too. Yes, and probably because of the angle.

And what is the second smaller concentric ring beyond the rotor?

I think that is the boundary between the valve casing and the brass tube it connects to which is going away from the camera in that perspective.

And what on earth is that little blob near the center of the photo? Did you get an M&M stuck in your valve?

The blob is a droplet of water.

That makes sense. Then we're looking through the rotor, not at it. So is it just poorly assembled? Because the valve knuckle should mate flush with the valve tubing. You shouldn't be able to see a "lip" like that where they connect.

[peteedwards]

Some manufacturers do make the rotor bore oversize, assumingly to
1) improve the air flow (it does NOT improve the sound wave path, however)
2) allow more tolerance in valve alignment

All those sudden bore steps, sharp corners and nooks and crannies are detrimental to the sound path and can certainly cause "wanky" (or wonky) notes & wolf tones, even occasionally. .

[harrisonreed]

Do your valves have RELIABLE witness marks? And are they lining up very precisely?

I don't know about the witness marks, but I think it's clear that it is NOT lining up properly.

This means that your bumpers need adjustment.

[timothy42b]

Some manufacturers do make the rotor bore oversize, assumingly to
1) improve the air flow (it does NOT improve the sound wave path, however)
2) allow more tolerance in valve alignment

All those sudden bore steps, sharp corners and nooks and crannies are detrimental to the sound path and can certainly cause "wanky" (or wonky) notes & wolf tones, even occasionally. .

I wonder if there is a way to make the alignment less critical, so that a little off in either direction matters less.

[Sesquitone]

Some manufacturers do make the rotor bore oversize, assumingly to
1) improve the air flow (it does NOT improve the sound wave path, however)
2) allow more tolerance in valve alignment

All those sudden bore steps, sharp corners and nooks and crannies are detrimental to the sound path and can certainly cause "wanky" (or wonky) notes & wolf tones, even occasionally. .

I wonder if there is a way to make the alignment less critical, so that a little off in either direction matters less.

Short answer: NO! Even with the rotor bore oversized to supposedly "allow more tolerance", the sound wave going into the valve (from either direction) sees a step out in bore, then a step back in as it exits—both of which cause unwanted reflections—resulting in distortion in overtone alignment, thereby affecting tone quality and attack response. Seamless transition into and out of the valve (i.e. "perfect" alignment of stops and no discontinuities inside the valve) is what we must aim for. Stop misalignment is probably one of the most undetected causes of "problems" on any brass-wind instrument. Even if you have reliable witness marks, the conventional way of aligning (razor shaving in one direction) is tricky. That's why I'm a strong advocate of individually adjustable stops (that can each be adjusted in either direction).

[hornbuilder]

Brad said... "So is it just poorly assembled? Because the valve knuckle should mate flush with the valve tubing. You shouldn't be able to see a "lip" like that where they connect."

Yes. The vast majority of factory built instruments have steps in the bore and/or gaps under ferrules. At every joint! Thanks to parts not being cut square and/or cut short.

[brassmedic]

Brad said... "So is it just poorly assembled? Because the valve knuckle should mate flush with the valve tubing. You shouldn't be able to see a "lip" like that where they connect."

Yes. The vast majority of factory built instruments have steps in the bore and/or gaps under ferrules. At every joint! Thanks to parts not being cut square and/or cut short.