These valves are used to control the direction of hydraulic flow by electrical means. A spool is shifted by energizing a solenoid that is located at one or both ends of the spool. When a solenoid is energized, it forces a push rod against the end of a spool. A spool shifts away from the solenoid and toward the opposite end of the valve body (see Figure 5-29). In a spring-offset model, a single solenoid shifts a spring-loaded spool. When a solenoid is de energized, a spring returns a spool to its original position.
