Gas operated valve actuator

A gas-operated valve actuator for rotating the input shaft of a valve, the actuator comprising:

• a body,
• selector valve means mounted to the body for selecting and permitting gas flow through either a forward motor line connected between a gas source and a motor means or a reverse motor line connected between the gas source and the motor means,
• limit valve means mounted to the body in communication with each motor line for controlling the flow of gas in the respective line,
• motor means mounted to the body and operable by the gas from the gas source flowing through the selected motorline, the motor means connected to the input shaft for rotating it, and
• quick shutoff means for the limit valve means, the quick shutoff means mounted to the body and comprising:
• cam screw means mounted to the body in movable coaction with the input shaft via intermediate gears there between, said cam screw means having a fine pitched threaded portion and a course pitched threaded portion and a neutral area disposed between the threaded portions,
• major cam means movably mounted on the cam screw means, the major cam means provided with threads for coacting with the threaded portions of the cam screw means,
• tripping cam means movably mounted on the cam screw means, the tripping cam means provided with threads for coacting with the threaded portions of the cam screw means and disposed so that the major cam means moving on the fine pitched threaded portion moves to contact and urge the tripping cam means onto the course pitched threaded portion toward limit valve support means,
• limit valve support means pivotally connected to the body and supporting the limit valve means in open position, said limit valve support means disposed so that upon contact by the tripping cam means, the limit valve support means pivots thereby shutting off the limit valve means,
• control means for alternately shutting off the flow in the selected motor line when the input shaft reaches its travel limit.