ABSTRACT
Generally, the choice is among on-off solenoid valves, proportional solenoid valves, servovalves, and stepmotor-modulated valves. That last category is based on microprocessor-controlled stepmotors (also called stepping motors, or just steppers) built into each valve assembly, to mechanically position the valve spool. This chapter discusses the electrohyd.raulic (EH) principles that are behind all of them.
