Safety valve - for wells drawing from different strata

摘要

A safety valve for installation down a borehole comprises a sphere with a passage through it of the largest possible dia assembled in a holder and forming part of the line through which the oil or gas flows. The sphere is turned from a first closed position as it moves downwards to a second open position, by a sleeve in a hydraulic cylinder pressurised from teh surface. When for any reason the control pressure is reduced, a spring aided by the flow from below lifts a sleeve to move back the valve into the closed position.