Function principle in which a small pilot piston is deflected, the main control piston then follows by means of pressure actuation as long as the actuation lasts. As a rule the pilot piston is in the main control piston (Figure F 30).
This principle is used, e.g. on the moving coil controller or on the rotary servo valve for a torque amplifier.
The slave piston principle can also be of electrical design if the pilot element and the main control piston are connected with a double closed loop position control system (Figure F 31).
Figure F 30: Mechanical slave piston principle
Figure F 31: Electrical slave piston principle