Patent ID: 8539975
Filing Date: 2013-09-24
Classification: E21B,Y10T

Abstract:
1. A drill string valve, comprising: a tubular housing having an axis and threaded upper and lower ends for connection into a drill string; an axially movable valve element mounted in the housing, the valve element having a closed position and an open position that allows drilling fluid to be pumped downward through the housing; a spring in cooperative engagement with the valve element for biasing the valve element to the closed position; a compensating piston movably carried in the housing, defining a compensating chamber, and being in cooperative engagement with the valve element; an annulus fluid port extending through the housing into the compensating chamber for admitting into the compensating chamber drilling fluid from an annulus surrounding a well and causing the compensating piston to exert an annulus force to the valve element corresponding to an annulus pressure of the drilling fluid in the annulus immediately surrounding the housing, the annulus force urging the valve element to the closed position; and a preload piston carried in the housing defining a preload fluid chamber between the preload piston and the compensating piston for receiving a preload fluid to preload the spring, the compensating piston transmitting the annulus pressure within the compensating chamber to the preload fluid chamber, the preload piston being in cooperative engagement with an end of the spring to apply the annulus force to the end of the spring in response to the annulus pressure being applied to the preload fluid chamber.