Patent ID: 7591216

Claim:
A valve actuator comprising: a housing formed of a single element, the housing including a cavity, and a first face including an opening; a first piston disposed in the cavity and attached to a first toothed rack; a second piston disposed in the cavity and attached to a second toothed rack; a rotary member exposed through the opening in the first face and including an axis of rotation and attached to at least one pinion mating with the first toothed rack such that the rotary member rotates in response to movement of the first piston; a first volume disposed in the cavity on a first side of the first piston; a second volume disposed in the cavity on a second side of the first piston; a third volume, disposed in the cavity on a side of the second piston opposite the second volume; a first fluid port disposed in the first face opposite the second volume as viewed along the axis of rotation of the rotary member and directly exposed to an exterior of the valve actuator so as to be directly accessible for connection to an external first fluid input, external to the cavity, and in fluid communication with the first volume via a primary fluid passage that extends, in a direction of travel of the first piston, from the first fluid port to an area opposite the first volume as viewed along the axis of rotation of the rotary member; a second fluid port disposed in the first face opposite the second volume as viewed along the axis of rotation of the rotary member and directly exposed to an exterior of the valve actuator so as to be directly accessible for connection to an external second fluid input, external to the cavity, and in fluid communication with the second volume; and a secondary fluid passage, internal to the housing, external to the cavity and separate from the primary fluid passage, connected to the first and third volumes so as to provide fluid communication between the first volume and third volume independently of the primary fluid passage.