Abstract: A critical state is assumed in which a position of one end of the opening of the input port in the axial direction and a position of the other end of the groove in the axial direction accord with each other with respect to the axial direction. In the critical state, when a straight line is extended in the axial direction as well as radially outward of the spool without changing a direction of the straight line in a circumferential direction of the spool from one end of the groove bottom in the axial direction with the same inclination as the inclination of the groove bottom at the one end of the groove in the axial direction relative to the axial direction, the straight line passes through the opening of the output port to contact a wall surface of the output port.

Abstract: A spool valve includes a sleeve and a spool. The sleeve has an inflow opening through which fluid flows in and an outflow opening through which the fluid flows out. The inflow opening opens in a radial direction of the sleeve and the outflow opening opens a same side with the inflow opening. The spool has a recess recessed from an outer peripheral part of the spool to a center axis of the spool. The spool is configured movable in the sleeve in an axial direction of the sleeve. The spool controls a communication state between the inflow opening and the outflow opening through the recess by regulating a position of the recess in the axial direction. A closed space is formed at a portion of the sleeve opposite to where the outflow opening is located.

Abstract: A critical state is assumed in which a position of one end of the opening of the input port in the axial direction and a position of the other end of the groove in the axial direction accord with each other with respect to the axial direction. In the critical state, when a straight line is extended in the axial direction as well as radially outward of the spool without changing a direction of the straight line in a circumferential direction of the spool from one end of the groove bottom in the axial direction with the same inclination as the inclination of the groove bottom at the one end of the groove in the axial direction relative to the axial direction, the straight line passes through the opening of the output port to contact a wall surface of the output port.