What, exactly, is the difference between a servo and proportional valve?
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. An extensive research project at the Fluid Power Institute was conducted to determine how a user could distinguish between a proportional valve and a servovalve. We used electronic enhancements to determine the extent to which a proportional valve could be made to perform like a servovalve. Performance characteristics and construction and manufacturing methods were examined. The most significant discriminator was the amount of center overlap. We eventually defined a servovalve as one with less than 3% of cen
