Abstract: A spool valve comprises a slidable spool, and through displacement of the spool a supply port of the valve is allowed to communicate with one of the load ports of the valve while the other load port is allowed to communicate with a corresponding one of return ports of the valve. The spool is provided with a portion, the outside diameter of which gradually increases, at least on the other load port side from the center of a central concave portion of the spool. The outside diameter gradually increasing portion decreases fluid force which acts against an operating force of the spool when the valve is activated.

Abstract: A spool valve comprises a valve body formed with a slide hole therein, a spool slidably received in the slide hole, a supply port, two load ports and two return ports, all of which ports are formed in the slide hole. The load and return ports are disposed with the supply port being the center. The spool has a central concave portion and two land portions, and with the displacement of the spool, the supply port is allowed to communicate with one of the load ports while the other land port is allowed to communicate with a corresponding one of the return ports. The spool is provided with a portion, the outside diameter of which gradually increases, at least on the other load port side from the center of the central concave portion. The outside diameter gradually increasing portion is formed in a conical shape, a curved drum shape, a stepped columnar shape or the like.