Air Flow in Valves
By Ron Yost
Hello all,
While we're discussing the very interesting subject of pneumatics, force, etc., I'd like to ask a couple of questions about valves in automatic instruments, and pipe organs in particular.
This would help a great deal in designing my organs, and I'm sure others have wondered about this and not seen it 'spec'd' anywhere.
If you have a round leather valve, say 3/4" diameter, covering a 1/2" diameter hole (1/8" overlap for proper sealing), how far does the valve need to open for_maximum_air flow through the hole (assuming the valve is lifted straight up and down)? I've been told the maximum flow is achieved with the valve lifted to 1/4 the valve diameter. Is this correct (or close enough for organ work)? Is there a practical 'rule of thumb' one can use for such things, or does it involved complicated calculation every time?
How about electric pipe valves? My experience building pipe chests using electric pipe valves (Reisner, Peterson and the like - where the valves are opened on a slight angle because of the geometry of the valve) tells me the maximum flow is achieved with lift that is less than 1/4 the diameter of the valve. It seems as though it's reached with very little lift - about 1/8" at the 'front' of the round pallet valve. My old ears don't hear any appreciable increase in the sound level of a pipe beyond that point.
For maximum repitition it's important to have the valve open as little as possible to achieve the correct sound level. These valves are fairly high-mass (there's quite a bit of iron moving around), so I'd guess you'd need to limit the travel to as little as necessary.
How about rectangular pallet valves used in pipe organs, where the valve is leather-hinged at one end? It's been my experience with pallets that once you overcome the pressure holding the valve closed, it doesn't make much difference how far it's opened beyond that point. In other words, once you 'crack' the valve it seems to assume maximum air flow very quickly, with very little 'lift'. This is probably because of the relatively large length of the slot compared to the narrow width.
I'd really appreciate anyone contributing their vast knowledge to this fundamental, but overlooked, subject. Thanks a lot!
Ron Yost <ryost@fix.net>
646 Bolen Drive.
Paso Robles, CA 93446-2760
805-238-1071 |
(Message sent Sat 23 Mar 1996, 21:44:45 GMT, from time zone GMT.) |
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