Importance

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Abstract

A hydraulic system for precise positioning of a control device, such as a valve actuator. A double-acting, hydraulic cylinder, which operates the control device, is held in any set position by a hydraulic lock ensured by one-way check valves which prevent interflow between the chambers on opposite sides of the piston. Occurrence of a signal indicating a need to change position activates one of two three-way directional control valves allowing exhaust flow from the appropriate cylinder volume. Connected in parallel in the exhaust line is a plurality of on-off valves, each having a flow capacity that is some multiple of that of the next smaller valve, e.g. twice as large. This provides a wide range of distinct and precise flow capacities to provide close and instantaneous control over rate of movement of the positioning device.

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First Claim