Posted by Rick Denney on August 27, 2000 at 17:29:23:
In Reply to: Re: Re: Re: Venting Piston Valves posted by Chuck on August 27, 2000 at 11:58:47:
I agree, which is why I'm asking. I've never heard reports of a corrosion problem, but I'm casting the net widely to make sure there are none before I assume anything. I can't remember ever hearing a report of problems resulting from the procedure, even with plain brass valves.
Of course, the valves on my Yamaha are Monel, but the bottom donut on the inside of the valve is brass, as it the bottom cap on the valve casing (and, for that matter, the casing itself). Even through crud builds up in the cap, I've never seen corrosion there once the crud was cleaned away.
As to why some factories don't do it, I wonder why not. The valves on Daellenbach's Schilke/Yamaha prototype were vented (he showed it to me as a recommendation to have it done to my 621), and as I read about the instruments of pros famous enough to disclose such details, I see that most have had the procedure done. Is it really not done on any factory models? Not on Yorkbrunners, or Nirscl-Yorks, or the like? Did Jacobs have the valves on the CSO York vented? What about other big-time players?
Miraphone pro horns have come both ways. My 186 BBb was not vented (I vented the first valve), but my friend's 186-5U CC was vented by the factory on all four valves. It seems to me the risk of venting rotary-valve casings exceeds that of piston valves by a long shot, and I know of a few who have sealed up the valves after adding a main-slide tuning stick (so that they were no longer manipulating valve slides). Wear on rotary valves can cause a leak at the vent in ways not likely with pistons.
Rick "Anybody with horror stories?" Denney