Installing New String
Most rotary valves are rotated with string. These strings wear out and have to be renewed. This is a simple operation, as shown by the accompanying diagram, Fig. 26. The first step is to loosen the string set screws. There are two of these: No. 1 on the key extension lever and No. 2 on the stop arm. Remove all old string and cut a new piece the same length. Usually this is about 6 or 7 inches long. A good grade of linen fish line with about 27-pound test makes a suitable string.
Tic a substantial knot in the end and start the string through the hole in the key extension lever, leaving the knot on the side of the lever away from the valve. Give the string a strong but steady pull to seat the knot in the hole. Then pull the string around the stop arm hub and encircle No. 2 string set screw. Note the direction of encirclement of the set screw is clockwise, the same direction in which the set screw turns when it is tightened. Also note that the return loop around the set screw is underneath. Also note that after the string is brought around the other side of the stop arm hub it crosses under the string on its way to the hole in the end of the key extension lever. The rest is easy: first through the hole and then encircle No. 1 string set screw in a clockwise direction, bringing the return loop under, the same as for string set screw No. 2.
Now that the string is threaded properly, pull the string so it is taut throughout, then tighten string set screw No. 1. If you work a key lever now, the string simply slides around string set screw No. 2 and the valve doesn't rotate. The next thing to do is to lower the valve key to the height to which you are accustomed and finally tighten string set screw No. 2. Usually you will find that you have pulled the string a little too taut for the rotor to turn freely; if so, loosen the string set screw No. 1 part of a turn or just enough to slacken the string a trifle. When the rotor turns freely, re-tighten the screw. Some players put a toothpick or match as a wedge between the key extension arm and the string, about a quarter of an inch below the knot. After the stringing is completed, the wedge is removed; this relieves the tension just about the right amount to allow the rotor to work freely.
Most players leave about 1 3/4 inches of string extending beyond string set screw No. 1 so they have a good hold on the string in case it needs retightening later. After several days the string may stretch enough to be too loose. If so, loosen No. 1 set screw, pull string taut, and retighten screw.
This diagram of stringing may not exactly suit certain valves, especially European makes. To avoid crossing the strings so they rub and saw against each other, try crossing them differently so they will work freely.