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...http://www.google.es/patents/US4596293?utm_source=gb-gplus-sharePatente US4596293 - Targetable drill with pressure telemetering of drill parameters
Targetable drill with pressure telemetering of drill parameters
