Posted by Rick Denney on May 01, 2001 at 16:39:39:
In Reply to: Re: Valve venting? posted by Dan on May 01, 2001 at 14:52:28:
For a rotary, in addition to my other comments, I would probably only vent the first valve. Drainage isn't an issue with a rotary, but it is really nice to be able to adjust that first slide without worrying about adding a bit of unscripted percussion to the ensemble sound. I've never missed the vents on the 2nd, 3rd, and 4th valves on my Miraphone, but I'd like vents on all the piston valves on my York.
You need a small hole in the rotary casing exactly between the two valve-tubing ports. By small, I mean that 2 mm seems about right. Any smaller, and the air rushing through the hole makes a too much of a whistling noise. Any larger, and you run the risk of getting too close to the port. Some of the repair dudes might chime in to disagree, and you should listen to them.
When I vented the first valve of the Miraphone, I took a drill bit, mounted it in a jeweller's screwdriver handle, and cut the hole by twirling it at the end of my fingers. No other tool would nestle between the valve tubes. Remove the rotor, drill the hole (exactly centered!), check the back side of the hole for shavings and burrs, but remove them carefully (i.e. not with sandpaper) so as not to ruin the seal around the hole when the valve is depressed. Flush out the shavings, reassemble the valve, and you're done. Figuring out how to turn the drill bit is the hard part, but overall it's much less scary than venting a piston valve. The whole thing took me less than 20 minutes.
Note that some highly-regarded performers and repair dudes don't like the idea of venting rotary valves, and you should take their opinions under consideration if they offer them.
Rick "if this confuses you, seek professional help" Denney