Rotary Valve Port Sizes?

[jorymil]

Hi folks,

I took apart an old King 605F bell last night. I was curious about valve and tubing sizes in the F attachment, so broke out the calipers. I was surprised: the port diameter of the rotary valve is less than 0.5": it measured out at 0.497 (error bar estimated at +/- 0.002"). Is there a table out there of various horn/valve models and their respective valve port sizes? If not, anyone interested in starting one with me?

Practically speaking, a small port size like this means I probably won't use this valve section on anything .500 bore or larger: it'll stay paired with a smaller bell and a sub-.500 slide.

John

[Doug Elliott]

I would go by how it plays, not a number.
The slide is .491, right? So anything around .500 is a totally logical size for the first thing past the slide bore. Nothing wrong with that as I see it. Except an F attachment on any horn that small would have limited usefulness. It's a student horn meant to allow a young player to have access to 6th and 7th position notes with the trigger. Nothing more.

[Burgerbob]

42Bs and 50Bs are said by many to have undersized rotors, and yet some of them play amazingly as-is. Like Doug said, if it plays well... it plays well. Who cares about numbers.

[Crazy4Tbone86]

Many rotor cores have oval-shaped ports. Thus, when your measure across the port, that measurement might be smaller than the measurement taken at a 90 degree angle. But alas, it could be tricky to measure that angle because the inside of the casing determines that.

As the other comments noted, it all comes down to...."does the horn play?" There are many places of slightly oversized tubing or constricted tubing on well-respected instruments that seem to work very well. Chances are that these acoustical oddities were discovered by accident and they stuck with it.

[JohnL]

I get the impression that the OP is looking to repurpose the 605F valve; in that case, you kinda have to go with the numbers.

[jorymil]

Yes - I bought a spare bell for $10 off eBay a while back with the idea of repurposing the valve section. Thought it might do well on a Yamaha 3xx bell or a Bach 16 bell.

But I'm generally curious about the engineering that goes into instruments. And in this case, the spectrum of rotary (and other valves): for example, if there's overlap between french horns (single) and small-bore trombones, or on the other spectrum, between bass trombones and rotary tubas. Brian's post hit the nail on the head: I hadn't realized that valve ports were often oval in cross-section. I could also see them potentially being non-cylindrical as well, and learning by exploring is part of the fun.