Abstract: Disclosed is an apparatus for vibrating a downhole drill string operable to have a drilling fluid pumped therethrough. The apparatus comprises a tubular body securable to the drill string and having a central bore therethrough, a valve in the tubular body for venting the drilling fluid out of the drill string and a valve actuator for cyclically opening and closing the valve. The method comprises pumping a drilling fluid down the drill string and cyclically venting the drilling fluid through the valve so as to cyclically reduce the pressure of the drilling fluid in the drill string. The valve can comprise a tubular body port and a corresponding rotor port selectably alignable with the tubular body port as the rotor rotates within the central bore. The valve actuator can comprise at least one vane on the rotor for rotating the rotor as the drilling fluid flows therepast.

Abstract: Disclosed is an apparatus for vibrating a downhole drill string operable to have a drilling fluid pumped therethrough. The apparatus comprises a tubular body securable to the drill string and having a central bore therethrough, a valve in the tubular body for venting the drilling fluid out of the drill string and a valve actuator for cyclically opening and closing the valve. The method comprises pumping a drilling fluid down the drill string and cyclically venting the drilling fluid through the valve so as to cyclically reduce the pressure of the drilling fluid in the drill string. The valve may comprise a tubular body port and a corresponding rotor port selectably alignable with the tubular body port as the rotor rotates within the central bore. The valve actuator may comprise at least one vane on the rotor for rotating the rotor as the drilling fluid flows therepast.