3-position actuator

A 3-position actuator having a moving body comprising a piston slidingly reciprocating for a specified distance in an axial direction within a casing having an inner surface of substantially constant diameter, and a piston rod which moves integrally with the piston and a part of which protrudes out of said casing, said moving body being moved to one end side when fluid flows into a first fluid chamber through a first port formed on said casing, and said moving body being moved to the other end side when fluid flows into a second fluid chamber through a second port formed on said casing;

• characterized by that a pair of stoppers are installed in said casing with a specified clearance left between them in the axial direction, one stopper of said pair of stoppers comprising a snap ring disposed on an axially central portion of said inner surface of substantially constant diameter of said casing, a pair of spring seats and a spring are installed between the pair of stoppers, said spring is located between the pair of spring seats to press one-side spring seat against said one-side stopper and to press the other-side spring seat against said other-side stopper, a pair of stopping portions are provided on said moving body in a projecting manner with a specified clearance left between them in the axial direction, said one-side stopping portion mates with said one-side spring seat from a side opposite to the spring under a state where said one-side spring seat contacts with said one-side stopper, and said other-side stopping portion mates with said other-side spring seat from the side opposite to the spring under a state where said other-side spring seat contacts with said other-side,
• wherein said piston rod comprises male threads formed on an outer periphery at one end of said piston rod for screwing into said piston, and wherein the moving distance of the moving body to one end side is made adjustable by rotating said piston rod within said piston.