A downhole tool includes a tubular having an outer surface and an inner surface defining a flowbore having a longitudinal axis and a backpressure valve arranged in the flowbore. The backpressure valve includes a flapper valve including a hinge end, a cantilevered end, a first side and an opposing second side pivotally mounted to the inner surface at the hinge end to selectively extend across the flowbore, and a locking system mounted to the inner surface adjacent to the hinge end of the flapper valve in the flowbore. The flapper valve is pivotable between a first position, wherein the flapper valve is free to pivot relative to the inner surface between an open configuration and a closed configuration, and a second position, wherein the hinge end of the flapper valve activates the locking system to lock the flapper valve in the open configuration.