Jack Johnson has spent his entire career dealing with the issues of electrohydraulic control systems, involving both the design of equipment and teaching the underlying principles at the Milwaukee School of Engineering and educator at seminars. He also served as the director of the Fluid Power Institute at the Milwaukee School of Engineering. Presented here is a small collection of questions that recur through the years, along with answers. For more information, contact him via e-mail.
Q: I’m confused about servo and proportional valves because the differences don’t seem clear-cut. What, exactly, is the difference between a servovalve and a proportional valve?
A: The generic descriptive term that applies to this class of valves is, “continuously variable, electrically modulated, hydraulic directional control valves.” Germans use the term stetigventil—a continuously differentiable valve, and servovalves and proportional valves fall within this generic valve type. Unfortunately, we have no single word in English to cover these valves. The generic term should be “proportional valve,” with two subcategories: servovalves and proportional valves.