Posted by Rick Denney on June 22, 2000 at 13:36:04:
In Reply to: Questions posted by Educable, but green on June 22, 2000 at 12:36:30:
The purpose of venting a valve is not as you say, at least for the venting I'm thinking of. The purpose is really to vent the valve *tubing*, not the valve. Vented tubing allows the slide to be pushed in and out without compression, which is useful for slides moved while playing and for emptying water.
Ventilation of the valve tubing for pistons is accomplished by a small hole in the portion of the valve that faces the valve tubing when the valve is *not* depressed. This ventilates the tubing through the hollow valve and the holes in the bottom of the valve and casing. The vent hole should be made in the bottom-most port so that it faces nothing but brass when the valve is depressed. After being shown where by looking at Chuck Daellenbach's horn during a master class, I did the same thing on my YFB 621 using a dremel tool and a cutoff wheel. My opening is a small slot running along the length of the valve, about 1 mm by 6 mm. His was a hole, but slots are much easier to machine without a lathe than a hole, at least without mangling the valve.
For rotaries, the ventilation is accomplished with a small hole in the casing between the two valve-tube ports. This vents the open portion of the rotor between the two ports. The hole must be placed correctly, though, or it will cause leakage when the valve is depressed. I did this on the first valve of my Miraphone (some Miraphones have this done already), using a 1 mm drill bit in a pin handle, and spinning the bit by hand.
Rick "Well ventilated" Denney