In a system including a fluid motor means;
- means for supplying pressurized fluid from a pressure source to energize the fluid motor means;
- a switch means having a first switching state in which pressurized fluid is introduced from the pressure source to the system and a second switching state in which communication is blocked between the pressure source and the system and the system is depressurized;
- the improvement comprising
- a. a sole first pressure conduit having a first end and a second end;
- said first end being connected to the pressure source with the interposition of said switch means;
- b. an actuator including
- 1. a cylinder having a cylindrical wall defining a pressure chamber to which said second end of said first pressure conduit is connected and an exhaust chamber;
- 2. at least two coupling ports provided in said cylindrical wall;
- said ports being axially spaced from one another;
- 3. a guide pin secured to said cylindrical wall and projecting into a space bounded by said cylindrical wall;
- 4. a piston disposed in said cylinder with a close fit and arranged for axial and angular displacement;
- said piston having a cylindrical lateral surface and a radial end face which bounds said pressure chamber;
- said piston separating said pressure chamber from said exhaust chamber in a fluidtight manner by a first sealing means carried by said piston;
- said piston having a first axial position and a second axial position;
- 5. means defining a passage between the cylindrical wall of said cylinder and the cylindrical lateral surface of said piston;
- 6. pressing means urging said piston in said first axial position;
- said piston being moved into said second axial position by the pressurized fluid when admitted into said pressure chamber from said pressure source through said first pressure conduit;
- said piston being moved into said first position by said pressing means upon depressurization of said pressure chamber;
- 7. means defining a helically extending groove in the piston surface;
- said guide pin projecting into said groove for effecting a rotary motion of predetermined angle of said piston during axial movement of said piston from one of its positions into the other;
- 8. a bore extending into said piston from said radial end face;
- 9. axially spaced channels provided within said piston;
- said channels starting at said bore and terminating at said cylindrical lateral surface of said piston;
- said channels establishing communication between said pressure chamber and a selected one of said ports when said piston is in said second position;
- the magnitude of the predetermined angle being such that upon each successive arrival of said piston into said second position a different one of said ports communicates with said pressure chamber;
- in said first axial position of said piston each said coupling port is in communication with said exhaust chamber through said passage and in said second axial position of said piston each said coupling port other than that pressurized from said pressure chamber is in communication with said exhaust chamber through said passage;
- 10. second sealing means carried by said piston and individually surrounding the mouth of each said channel on said cylindrical lateral surface of said piston;
- said second sealing means being in engagement with the cylindrical wall of said cylinder for blocking communication, in said second axial position of said piston, between said exhaust chamber and any coupling port pressurized from said pressure chamber;
- and
- c. second pressure conduits equalling the number of said ports;
- a separate one of said second pressure conduits being connected, at one end, to a separate one of said ports and, at another end, to said fluid motor means.