Abstract: Methods and apparatus for filling a tubing string as it is lowered into a subterranean hydrocarbon well. In one embodiment, an apparatus to fill a tubular with fluid in a wellbore comprises a housing defining a central bore. An aperture formed in the housing provides fluid communication between the central bore and the ambient environment of the tubing string. A piston valve slidingly disposed in the housing is selectively pressure actuatable relative to the housing to control fluid communication between the central bore and the ambient environment.

Abstract: Methods and apparatus for filling a tubing string as it is lowered into a subterranean hydrocarbon well. In one embodiment, an apparatus to fill a tubular with fluid in a wellbore comprises a housing defining a central bore. An aperture formed in the housing provides fluid communication between the central bore and the ambient environment of the tubing string. A piston valve slidingly disposed in the housing is selectively pressure actuatable relative to the housing to control fluid communication between the central bore and the ambient environment.

Abstract: A bi-directional plug blocks the flow of fluid through a flow bore of a tubing string and can be opened by simple mechanical means requiring no external tools. A piston is slidably mounted in a piston housing and fixed in a first position with a plurality of shear screws. An atmospheric chamber formed within the piston housing creates a pressure differential causing the shear screws to fail when a certain pressure is applied to the surface area of the piston. When the shear screws break, the piston accelerates and strikes a scored, dome-shaped plug. The piston penetrates the plug, permanently pressing and housing pieces of the plug against the wall of a plug housing and opening the flow bore of the plug to fluid.