Rotary valve operator includng operating and centering piston assemblies

Claim 1

A VALVE OPERATOR FOR SELECTING A VALVE POSITION, COMPRISING: A HOUSING; A SHAFT ROTATABLE AROUND AN AXIS IN SAID HOUSING, SAID SHAFT HAVING A FIRST AND A SECOND PAIR OF REACTION SURFACES THE MEMBERS OF THE FIRST PAIR AND OF THE SECOND PAIR OF SAID REACTION SURFACES BEING RADIALLY SPACED FROM SAID AXIS BY A FIRST AND A SECOND DISTANCE, RESPECTIVELY; A FIRST AND A SECOND PAIR OF FORCE MEANS, COMPRISING A PISTON-CYLINDER ASSEMBLY, THE TWO ASSEMBLIES OF THE FIRST PAIR BEING ADAPTED SIMULATANEOUSLY TO BE JOINED TO A COMMON SOURCE OF POWER, THE TWO ASSEMBLIES OF THE SECOND PAIR BEING ADAPTED SELECTIVELY AND INDIVIDUALLY TO BE CONNECTED TO SOURCE OF POWER, THE CROSS-SECTIONS EXPOSED TO POWER OF THE ASSEMBLIES OF THE SECOND PAIR OF FORCE MEANS BEING GREATER THAN THOSE OF THE FIRST PAIR, EACH SAID PAIR OF FORCE MEANS INCLUDING TWO ELEMENTS, THE ELEMENTS OF EACH OF SAID LAST-NAMED PAIRS BEING OPPOSITELY DIRECTED AGAINST A RESPECTIVE ONE OF THE REACTION SURFACES OF A RESPECTIVE PAIR THEREOF; A FIRST AND A SECOND PAIR OF STOP MEANS, EACH PAIR OF STOP MEANS COMPRISING A STOP MEMBER RESPECTIVE TO ONE OF SAID ELEMENTS AND OBSTRUCTIVELY IN THE PATH OF MOVEMENT THEREOF, THE ELEMENTS OF THE FIRST PAIR OF FORCE MEANS BEING COUPLED TO PRODUCE SIMULTANEOUS EQUAL AND OPPOSITE TORQUES ON THE SHAFT THROUGH THE RESPECTIVE FIRST PAIR OF REACTION SURFACES, THE ELEMENTS OF THE SECOND PAIR OF FORCE MEANS BEING ADAPTED TO EXERT NON-SIMULTANEOUS FORCES ON THE REACTION SURFACES OF THE SECOND PAIR OF A MAGNITUDE TO OVERCOME THE TORQUE OF THE OPPOSING FORCES ON THE FIRST PAIR OF SAID REACTION SURFACE SO AS SELECTIVELY TO TURN THE SHAFT TO A FIRST OR A SECOND OFF-CENTRAL POSITION AND, WHEN THE FORCES ARE EQUAL ON THE ELEMENTS OF THE SECOND PAIR OF FORCE MEANS, TO ENABLE THE FIRST PAIR OF FORCE MEANS TO TURN THE SHAFT TO A CENTRAL POSITION, THE FIRST PAIR OF STOP MEANS PREVENTING THE FIRST PAIR OF FORCE MEANS FROM TURNING THE SHAFT TO AN OFF-CENTRAL POSITION, AND THE SECOND PAIR OF STOP MEANS PREVENTING THE SECOND PAIR OF FORCE MEANS FROM TURNING THE SHAFT PAST RESPECTIVE OFF-CENTRAL POSITIONS.