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.

Abstract: A dirigible drilling head is provided with a hydraulic pulser in its rotating inner tube in the form of a spindle piston which can obstruct the flushing medium passage and is displaced by a hydraulic circuit including a hydraulic valve. The hydraulic valve is in turn actuated by a miniature electronic circuit so that a variety of input parameters from respective sensors can be delivered to the circuit and transformed into respective hydraulic pulses which are monitored by a differential pressure pickup connected to the line feeding the flushing liquid to the string.