Development of a water hydraulic servovalve

An electrohydraulic servovalve that uses fresh water as a pressure medium (water hydraulic servovalve) is developed. A conventional electrohydraulic servovalve cannot be operated with such a hostile fluid. In this paper, we explain the structure and functions of components, and the relationship between them, as well as the developmental procedure of the water hydraulic servovalve. The basic idea for the servovalve is to support the spool of the valve with hydrostatic bearings and to lead the water from the bearings to the flapper-nozzle system. The hydrostatic bearings constitute a laminar restriction that takes the place of the turbulent restriction in the conventional flapper-nozzle system. We also explain the design procedure of the hydrostatic bearing in the valve and the relationship between electromagnetic elements and fluidic elements. The water hydraulic servovalves fabricated show good characteristics of smooth motion, endurance and controllability, as well as good dynamic characteristics.