Installing New Corks
When the valve key is up, the valve parts are in the position indicated in view A. When the valve key is pushed down, the parts change to the positions indicated in view B. Note that the position of marks (3), (4), and (5) have changed so that (5) is now directly below (3), and the marks (4) and (5) have moved around so that they are in the position of the hands of the clock when it is a quarter past 12 o’clock. The by-pass through the valve has been closed and the air column is now directed down through the valve slides. The stop arm has moved to the upper cork. This understanding of how the valve operates is necessary before you can do an intelligent job of installing new cork bumpers.
The actual installing of the corks is simple. Press a piece of cork into the jaws of the cork stop plate. It will be held there by friction fit; on certain makes the cork must be glued in. Cut the cork larger than the adjustment requires so you can shave it away until correct adjustment is secured. After both corks are in, cut the cork back with a razor blade or sharp knife until the two conditions of Fig. 28 are met. Referring to view A, when the stop arm is pressed firmly against the lower cork, the marks on the back of the valve should be at 9 o’clock. Referring to view B, when the stop arm is pressed firmly against the upper cork, the marks on the back of the valve should be at a quarter past 12 o’clock.
It is important that the guide marks on the back of the valve are accurately set, for these marks determine where the port in the rotor meets the knuckle in the casing. If the marks are slightly off register, the ports in the rotor do not quite meet the knuckles, and the horn will blow stuffy. Shave the corks carefully so the marks register accurately; then you will have a free-blowing horn.