Servo controls that are Star Servo valves, utilise a jewelled feedback ball on their feedback wire assembly so that servo valves will have longer span of operation before "Glitch" effect. Star Servo valves are available from Hylec Controls .
The feedback wire ball is made of sapphire, which is harder than diamond. Hence, there is no wear and tear on the ball and this prevents null shift and null drifting. The end orifices are also made of sapphire so that there is no wear and tear inside the orifice. Even contamination i.e. Micronics level, is cut into still smaller level and can increase the life of the servo valve.