US Patent 7926575 Hydraulic lockout device for pressure controlled well tools

Well tools are provided which although pressure responsive, may be maintained by a hydraulic lockout in a nonresponsive condition until a threshold actuation step is performed. This lockout may be achieved by a hydraulic mechanism which controls the rate at which pressure is transmitted to a fluid spring during periods of increased pressure at the pressure source. When the tool is desired to be responsive to pressure cycles, a valve may be opened by established a differential between the pressure in the fluid spring and the pressure source. Communication of pressure in the fluid spring to a movable mandrel will then allow operation of the well tool in response to pressure cycles at the pressure source in accordance with the established design of the well tool.