Safety and environment considerations necessitate the use of automatic emergency shut-off valves in nuclear power-plants, underground nuclear tests, oil pipelines and even oil wells. Such valves require actuators to move a member (e.g., a gate, a stem or a ball which may weigh hundreds of pounds) in a time that may be as short as a fraction of a second, and which must have some provision for decelerating the moving body at the end of its stroke to avoid a damaging impact. A device for satisfying these requirements with the high reliability required for such systems is proposed. This device consists of a double-acting piston driven by gas generated by the combustion of a propellant, with the novel feature of using a precisely determined straight hole through the piston to provide a gas cushion for deceleration during the last part of the stroke.nPredicting the performance of such an actuator required analysis and calculation of the rate of propellant gas generation, the rate of gas flow into the actuator cylinder, and that of gas flow through the piston hole. Because of the complexity of this analysis, a numerical solution was required. A computer subroutine for carrying out this solution was developed. Its applicability was verified by comparison of the predicted and experimentally measured performance of a specific actuator.
展开▼
