Vibrating downhole tool

1. A method of vibrating a downhole drill string, the method comprising:

pumping a drilling fluid down the drill string;

cyclically venting said drilling fluid through a valve in a side wall of said drilling string so as to cyclically reduce the pressure of said drilling fluid in said drill string; and

rotating a rotor within a tubular body located in-line within said drill string wherein said venting comprises intermittently passing said drilling fluid through a rotor port in said rotor and a corresponding tubular body port in said tubular body.

2. The method of claim 1 further comprising rotating said rotor with said drilling fluid.

3. The method of claim 2 further comprising separating said drilling fluid into a central bypass portion and an annular rotor portion, passing said bypass portion past said rotor and rotating said rotor with said rotor portion.

4. The method of claim 3 wherein said bypass portion and said rotor portion are combined after said rotor portion rotates said rotor wherein said rotor port and said tubular port pass said combined rotor portion and said bypass portion therethrough.

5. An apparatus for vibrating a downhole drill string, the drill string being operable to have a drilling fluid pumped therethrough, the apparatus comprising:

a tubular body securable to said drill string and having a central bore therethrough;

a valve in said tubular body for venting said drilling fluid out of said drill string; and

a valve actuator for cyclically opening and closing said valve;

wherein said valve comprises a radial tubular body port in said tubular body and a rotor located within said central bore having a radial rotor port wherein said rotor port is selectable alienable with said tubular body port as said rotor rotates within said central bore.

6. The apparatus of claim 5 wherein said valve actuator comprises at least one vane on said rotor for rotating said rotor as said drilling fluid flows therepast.

7. The apparatus of claim 6 wherein said rotor includes a central bypass bore therethrough and a plurality of vanes radially arranged around said central bypass bore.

8. The apparatus of claim 7 further comprising a separator for separating the drilling fluid into a bypass portion and a rotor portion secured within said central bore, said rotor portion being directed onto said plurality of vanes so as to rotate said rotor, said bypass portion being directed though said bypass bore of said rotor.

9. The apparatus of claim 8 wherein said separator includes a central bypass port and an annular rotor passage therearound.

10. The apparatus of claim 9 wherein said separator is located adjacent to said rotor such that said central bypass port of said separator directs said bypass portion of said drilling fluid though said bypass bore of said rotor and wherein said rotor passage of said separator directs said rotor portion of said drilling fluid onto said plurality of vanes of said rotor.

11. The apparatus of claim 10 wherein said rotor passage of said separator includes stator vanes for directing said rotor portion of said drilling fluid onto said plurality of vanes.

12. The apparatus of claim 9 wherein said bypass port of said separator includes an inlet shaped to receive a blocking body so as to selectably direct more drilling fluid through said rotor passage.

13. The apparatus of claim 12 wherein said inlet has a substantially spherical shape so as to receive a spherical blocking body.

14. The apparatus of claim 5 further comprising a plurality of rotor ports selectably alignable with a plurality of tubular body ports.

15. The apparatus of claim 14 wherein each of said plurality of rotor ports is selectably alignable with a unique tubular body port.

16. The apparatus of claim 5 wherein said tubular body is connectable inline within a drill string.

17. The apparatus of claim 16 wherein said tubular body includes threaded end connectors for linear connection within a drill string.