There are four basic servo systems as shown in Fig. 11.7. The two servo-actuator systems are (1) valve-motor and (2) valve-cylinder. These systems are often referred to as servo motors and servo cylinders. The recommended procedure is to mount the valve directly on the actuator. This avoids a column of compressed fluid in the lines and increases the natural frequency of the system, which increases positioning accuracy, as later analysis will show.
The two servo pump systems are (3) servo pump-motor and (4) servo pump-motor (split). Most accurate speed control is given by the servo pump-motor, because this configuration avoids a column of compressed fluid in the lines and thus gives a higher natural frequency for the system. There are times, however, when the pump and motor cannot be packaged together. The split configuration has the largest position error of the four configurations.
