Patent attributes
A selectively two directional check valve is located on a string with a packer and is either held open for running in so that the string can fill and doesn't become buoyant or includes a closable ported sub to allow string filling for running in that can then be closed. Pressure is applied from the surface to drive an object down to a seat so that a packer can be set. Further pressure increase shifts the object and the seat and locks the seat in the shifted position. A spring return force pushes the object to an upper seat to prevent uphole flow. Flow in the downhole direction is possible by overcoming the spring bias to move the object off the upper seat while preventing the object from moving down far enough to engage the shifted lower seat. Flow downhole just goes around the object.
