Patent ID: 8727040

Claim:
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 an open position that allows drilling fluid to flow through the housing into the drill string below the housing, and a closed position that blocks the flow of drilling fluid through the housing; a spring in cooperative engagement with the valve element for urging the valve element toward the closed position, the spring being located within a spring chamber in the housing that is filled with a liquid that differs from the drilling fluid; a separating piston movably carried in the housing within a drilling fluid chamber that is in fluid communication with the drilling fluid that has been pumped down the drill string, the separating piston separating the drilling fluid in the drilling fluid chamber from the liquid in the spring chamber; a spring chamber piston that has one side in contact with the liquid in the spring chamber, the spring chamber piston being cooperatively engaged with the valve element for moving the valve element in response to movement of the spring chamber piston; and wherein the separating piston is axially movable relative to the spring chamber piston.