why raised bumps inside valves

[Thermionman]

Helo all.....I am curious to why there are raised bumps inside certain valve passageways in the valves...........I noticed it in my Yorkmaster Eflat tuba......

[Michael Bush]

http://www.mawvalve.com/mawvalve.htm

[UDELBR]

At some point Conn and Holton (and others?) designed “short stroke” pistons, which, on a tuba, give the player a valve stroke much like that on a trumpet. I don’t know why these did not take off other than they may have been much harder to make back then. Who knows?

Yep. Here's what those valves look like:



I've read several studies which say the 'squashed' ports have virtually no detrimental acoustic effect.

[Thermionman]

Thankyou all for replies.........very interesting............

[Dan Schultz]

Here is Holton's solution to those 'raised bumps'...

[imperialbari]

The sore spot of both the Conn and the Holton variants of compressed ports is that they are more vulnerable to axial misalignment. If the felts are 1mm too thin or 1mm too thick, a bigger area of the short action ports will be blocked than the same misalignment would cause on valves with normal round ports.

Klaus

[roweenie]

At some point in their Grand Rapids production timeline (I'm guessing around the late '20s) York succumbed to the "short stroke" phenomenon. However, instead of inventing a new system, they just shortened the length of the piston:



This, of course, produced a bump, where previously there wasn't one:





(In addition, the York Master tuba must have been a copy of the later variety, as the pistons on those horns are also shorter with bumps. Also, the two pistons pictured above are both from .750 bore 7×× series tubas; they are identical in diameter and will fit in each other's casings).

On a side note, does anyone know which type of piston the CSO York tubas have? I'm guessing that since they were made in the early '30s (?) that they would be the shorter variety, but since they were essentially "one-off" (or "two-off") horns, that any variety is possible.

[Donn]

It seems to me that if critical alignment was the only problem with the Conn and Holton short stroke valve designs, everyone would have short stroke valves. I mean, if we can make internal combustion motors, we have the kind of advanced technology to deal with the alignment problem.

[imperialbari]

image.png

Is this really the patent application for the Holton short action system?

Holton uses an all ‘scooped’ out space plus the wall of the cylinder casing to guide the air between the entrance and the exit of the piston casing.

The drawings look like the Fairchild system uses an U-shaped tubing inside the piston to achieve the same goal.

Anyway the Fairchild system looks like being intended for a trumpet with top sprung pistons.

And yes, both systems build on the idea of bending the airstream tightly back right after it enters the piston.

Klaus

[Dan Schultz]

.... The drawings look like the Fairchild system uses an U-shaped tubing inside the piston to achieve the same goal....

It appears that figures #5 and #6 depict two variations of the patent... one with 'scooped' pistons and one with tubes built into the pistons.

The 'scooped' variant depends on a web in the casing to separate the air paths.

[imperialbari]

I don’t get web in this context.

Klaus

[Dan Schultz]

I don’t get web in this context.

Klaus

For each piston there are four flattened ports in the casings. There are webs between each set of ports that separate the 'scooped' piston passages into two circuits.

Difficult to comprehend without actually seeing the valve section. Even more difficult for me to make a descent drawing of exactly what's happening.

[Donn]

So ... since I might likely be confused here, we're lately speaking about the version depicted in Figure 6 of the patent drawing?

And someone has actually seen this, as opposed to the drawing - these pistons were produced and used in tubas?

[proam]

Something from a one-time custom trumpet maker in England. I believe he has now retired.

http://www.deniswedgwood.com/ovoids.html" target="_blank

[Dan Schultz]

So ... since I might likely be confused here, we're lately speaking about the version depicted in Figure 6 of the patent drawing?

And someone has actually seen this, as opposed to the drawing - these pistons were produced and used in tubas?

Unless I have my 'wires crossed'.... figure #6 represents the 'scooped' style of pistons that were used in Holton short-action tubas and sousaphones. I have one of each here that would make great 'book-ends' in someone's collection.

[Donn]

OK, as I suspected. As you may remember I have one of those, too, and I didn't get the web thing either, though it's at the shop right now so I'm just going from memory. Anyway, maybe there's no point in getting to much into the details - I think the illustration actually pretty much covers it.

Have you thought about that design from a damage/repair perspective? Would the case be kind of weak on the port side, because so many openings in a row?

[Dan Schultz]

....Have you thought about that design from a damage/repair perspective? Would the case be kind of weak on the port side, because so many openings in a row?

I actually think the Holton design is pretty solid. EXCEPT for the fact that there's not much 'fudge factor' on the alignment and that the design might be more prone to leak because of the increased seal perimeter.