ABSTRACT
The bias spring (9) serves to center the spool (8) when the pilot valve (3) is not actuated by either solenoid (1) or solenoid (2). Manual actuation can be accomplished by pushing the mechanical actuator (11). Energy flow to solenoid A will move the spool (4) and direct pilot flow to the cavity of spring (9). Resistance created by the movement of the spool and compressing of spring (9) is reflected to the small internal piston at the solenoid B end of pilot spool (4). Figure 13.25 provides an enlarged sectional view of the piston within the spool (item 4, Figure 13.24). In operation the internal piston tends to move the spool to the neutral position, blocking the flow to the cavity at the spring (9), and the piloted spool (8) stays in the partially shifted position until additional energy is directed or released from solenoid A. The position of piloted spool (8) is proportional to the energy flow to solenoids A or B within the design parameters of the valve assembly. Note the bleed screw at each end of the solenoid of Figure 13.25. At initial installation and/or after a repair has been
Figure 13.27 Servo valves provide precise control and repetitive accuracy. Available for pressures to 5000 psi (345 bar). Courtesy of Schenk Pegasus Corporation.
