Abstract: A rotary valve assembly for a rotary steerable tool is disclosed for directing flow of an abrasive laden drilling fluid; the valve assembly has a first sealing surface rotatably engaging a second sealing surface. At least one of the surfaces has at least about 5% of its area comprising interconnecting voids to an average depth of at least 0.02 mm. The interconnected voids allow fluid pressure to equalize between the sealing faces by flowing through the interconnecting voids to the sealing surfaces. Because the fit of the sealing surfaces of the valve is less than perfect, and because the voids on mating surfaces do not necessarily overlap, the 5% of the surface area comprising interconnected voids can easily translate to a 10% or more reduction in sealed area when both sealing surfaces have the interconnecting voids. The additional reduction in surface area subjected to differential pressure has substantially eliminated the hydraulic lock problem previously encountered upon startup.

Abstract: A rotary valve assembly for a rotary steerable tool is disclosed for directing flow of an abrasive laden drilling fluid; the valve assembly has a first sealing surface rotatably engaging a second sealing surface. At least one of the surfaces has at least about 5% of its area comprising interconnecting voids to an average depth of at least 0.02 mm. The interconnected voids allow fluid pressure to equalize between the sealing faces by flowing through the interconnecting voids to the sealing surfaces. Because the fit of the sealing surfaces of the valve is less than perfect, and because the voids on mating surfaces do not necessarily overlap, the 5% of the surface area comprising interconnected voids can easily translate to a 10% or more reduction in sealed area when both sealing surfaces have the interconnecting voids. The additional reduction in surface area subjected to differential pressure has substantially eliminated the hydraulic lock problem previously encountered upon startup.

Abstract: A rotatable pressure seal between a relatively rotatable shaft and body structure comprises two annular sealing discs concentric with the shaft, one disc being mounted on the body structure and the other disc being carried on the shaft the discs having engaging sealing faces formed of polycrystalline diamond or other superhard material. The pressure seal is particularly for use in a modulated bias unit, for controlling the direction of drilling of a rotary drill bit when drilling boreholes in subsurface formations. The bias unit comprises a number of hydraulic actuators spaced apart around the periphery of the unit, and a selector control valve modulates the fluid pressure supplied to each actuator in synchronism with rotation of the drill bit so that, as the drill bit rotates, a thrust member of each actuator is displaced outwardly at the same selected rotational position so as to bias the drill bit laterally and thus control the direction of drilling.