Patent ID: 7327634

Claim:
A rotary pulser for transmitting information from a portion of a drill string operating at a down hole location in a well bore, said drill string having a passage through which a drilling fluid flows, comprising: a) a housing adapted to be mounted in said drill string; b) a stator supported in said housing and having at least one approximately axially extending passage formed therein through which at least a portion of said drilling fluid flows; c) a rotor supported in said housing adjacent said stator and downstream therefrom, said rotor having at least one blade extending radially outward so as to define a radial height thereof, said rotor blade having upstream and downstream surfaces and first and second sides each extending between said upstream and downstream surfaces, said rotor being rotatable into at least first and second circumferential orientations, said blade imparting a varying degree of obstruction to said flow of drilling fluid flowing through said stator passage depending on the circumferential orientation of said rotor, said first rotor circumferential orientation providing a greater obstruction to said flow of drilling fluid than that of said second rotor circumferential orientation, whereby rotation of said rotor generates a series of pulses encoded with said information to be transmitted; and d) a motor coupled to said rotor for imparting rotation to said rotor, whereby operation of said motor generates said series of encoded pulses; e) wherein said first and second sides of said rotor blade are inwardly tapered in transverse cross-section as said first and second sides extend from said upstream surface to said downstream surface of said rotor blade so that said rotor blade imparts a torque to said rotor when said motor is not operating so as to reduce the obstruction imparted by said blade to said flow of drilling fluid when said motor is not operating.