I own a Schmid that was built in 1991 and I can give a few pointers: First, someone said that strings being too tight was a mistake on this horn, but I personally don't like any play with the string. Pulling the strings tight seems to not be a problem for me as the valves work fine that way. Second, it's relatively easy to isolate the problem and figure out exactly what is 'sticking'. Before doing any cleaning, unattach the valve from the mechanism. Move the mechanism back and forth at varying speeds and try to see if it catches anywhere. If it moves smoothly (and try pushing the lever down at an angle to test for horizontal play in the mechanism) then the problem is the valve. With a rotary valve, the precision has to be very close, but is not an exact fit on either the sides of the valve casing or on the bushing plates. (Technically they are not bearings, but bushings.) There has to be enough room for a thin film of oil and not too much room that air can escape the valve or you lose compression. Horizontal play in the valve itself is usually minimized because the _bushing_ keeps the valve centralized in the rotor. Yet, when a valve has been seated a certain way over a number of years, the slightest pressure on a valve could shave off a certain portion of the top or bottom bushing and cause it to be off center by a micrometer. It only needs the slightest bit of extra friction to stick anywhere. This is pretty rare though so it's probably not the problem. If I were to hazard a guess, it would be most likely vertical play in the valve caused by a bushing on the bottom or top moving. A valve isn't perfectly smooth and if you looked at one through an electron microscope you would find a lot of microscopic grooves that are caused by the valve rotating in the casing. These grooves over time find a 'sweet spot' in the valve casing since the wear is often not even and there are less grooves where there are holes in the casing. If you move the valve up or down slightly from where it has 'set in', then sticking can naturally occur exactly where the vertical play is occurring. You may not even be able to see it, but there is almost always some vertical force, however small, on just about any valve action. That's why bushing placement is important. The same can happen on the bearing plates with vertical play in certain spots, and can push grooves deeper in the bushing over some places. This is why on most older horns if you turn the top bushing to somewhere other than it is marked, the valve may not even move - and even if you do get the spot aligned it takes some fidgeting with the bushings sometimes to get the valve where it needs to be. It can also be dirt on the valves. So, I'd involve this procedure: 1. Unattach the mechanism and test the mechanism for any stickyness 2. With the rotor unattached, try to spin it horizontally and push it up and down vertically to test for any play. Spin the valve with the horn upside down to test for any stickyness along each bushing. 3. Take the top bushing off by lightly tapping a brass drift into the bottom screw hole 4. Spin the valve without the top bushing to test for stickyness 5. If you can remove the bottom bushing, then do so 6. Spin the valve by hand in varying spots throughout the valve to test for stickyness 7. If you can find any problem in the above steps, you'll know where in the valve it is occuring 8. Clean the rotors and bushings thoroughly. Do it ultrasonically if you can, if not a highly diluted solution of muriatic acid could also clean them but you also have to neutralize it afterwards with some sort of highly basic solution so I wouldn't recommend that if you've never done it before.) 9. Reassemble the valve going backwards from step 6, and test for stickyness again. By this point it should be gone. 10. If it's still there, take it to a pro who can either lap the valves, clean it more thoroughly, or do something else to make it better. -William In a message dated 1/30/2011 2:09:46 P.M. Eastern Standard Time, [email protected] writes:
I'm looking at the photo on the Schmid website. Does yours have the plasti c ball and socket connectors? Can you pop off one connector at a time so it's only operating one of the valves? Maybe you can isolate which one is sticking. Sometimes with a long lever, it can start to work badly if it's been bent just a little. Usually with a problem like this, I would just try to isolate and try each component one at a time. Maybe the lever itself has a catch, maybe one of the rotors, maybe the angle of the connector is off, maybe everything works well individually but with both valves hooked up, something about the action of one interferes with the other. Lots of possibilities, you just have to eliminate one by one. - Steve Mumford XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX Dan wrote: I am having problems with the change valve between low F and Bb in my F/Bb/f Schmid triple horn. It has a long lever and operates two valves on each side of the lever simultaneously. When I release the lever from Bb to F (I have the valves standing in F) there is often a little catch, or sticking. I have had two different repair guys look at it, both valves have been taken apart, and the strings and bumpers replaced, but it seems to be getting worse. Extensive daily oiling inside and outside the valves seems to help a little, but then the sticking will start up again for no reason. Has anyone run across this problem or does anyone have any suggestions? Dan _______________________________________________ post: [email protected] unsubscribe or set options at https://pegasus.memphis.edu/cgi-bin/mailman/options/horn/valkhorn%40aol.com _______________________________________________ post: [email protected] unsubscribe or set options at https://pegasus.memphis.edu/cgi-bin/mailman/options/horn/archive%40jab.org
