Abstract: A choker valve assembly for a drill string is provided for transmitting information measured in an underground bore hole by sensing devices, to the surface by modulating the pressure of the flushing fluid. The valve assembly includes a housing that is non-rotatably connected within the flushing fluid flow passage by cross-pieces extending between the housing and a portion of the inner pipe wall. A drag body valve element is mounted by the housing and is axially displaceable with respect to a tapered restriction portion of the inner pipe. Drive means for displacing the valve element is located outside the housing and extends between the valve element and the pipe wall through the cross-pieces. A cap is provided on each end of the valve element.