Abstract: A valve comprising a valve body having a tapered conical bore and an opposed inlet and outlet openings. A tapered cage abuts the conical bore. The cage is designed for easy replacement. A stopper is arranged within the cage. The stopper has a control vane extending radially outward from the stopper axis. Conical plugs are fixed at each axial end of the control vane. Biasing means urge the stopper toward the small end of the conical bore. A cam surface and cam follower lift the stopper axially away from the small end of the conical bore when it is rotated away from a closed position.