Force balanced hydraulic spool valve

In a hydraulic valve assembly including a body having a generally cylindrical internal cavity and a plurality of hydraulic ports through said body, said cavity defining an axis, said ports communicating with said cavity and adapted to convey hydraulic fluid to and from said cavity, wherein said cavity contains a plurality of radially oriented fluid control lands and grooves, said assembly further comprising an axially moveable cylindrical spool supported within said cavity, said spool also containing radially oriented fluid control lands and grooves adapted to interface with said lands and grooves of said cavity, wherein the intermediate portion of said cavity comprises an open center core portion, said hydraulic ports being adapted to admit hydraulic fluid under pressure into said center core portion, an intermediate portion of said spool defining a central land bounded on each side by an immediately adjacent groove and a power land, each power land axially spaced from said central land by the distance of said associated adjacent groove, each opposed axially spaced power land including a centrally directed notch on an edge of said power land adjacent its respective adjacent groove, each notch being adapted to direct a hydraulic fluid stream across said adjacent groove to one side of said central land, each side of said central land comprising an opposed piston face shaped for controlling postimpact radial flow components of said fluid stream;

• an improvement comprising at least one of said piston faces including an inner radially concave annulus and an outer radially concave annulus together defining a convex split point annulus boundary between them, said split point annulus positioned relative to one of said notches so as to generate inversely directed radial flows across each of said annuli from said split point annulus.