(19)
(11) EP 0 083 961 A3

(12) EUROPEAN PATENT APPLICATION

(88) Date of publication A3:
25.07.1984 Bulletin 1984/30

(43) Date of publication A2:
20.07.1983 Bulletin 1983/29

(21) Application number: 83300016

(22) Date of filing: 05.01.1983
(84) Designated Contracting States:
AT BE DE FR GB NL SE

(30) Priority: 06.01.1982 CA 393583

(71) Applicant: BRALORNE RESOURCES LIMITED
 ()

(72) Inventors:
  • Ring, Curtis Phillip
     ()
  • Tomm, Wayne R.
     ()

   


(54) Improved jar tool for drill strings


(57) A jar tool for use in a drill string for use in dislodging a drill bit or well-tools trapped in well bores. The tool comprises an outer housing adapted to move longitudinally with respect to an inner spline mandrell. A piston assembly is acted on by a piston actuator and hydraulic fluid restricts the movement of the piston assembly and, therefore, the movement of the mandrell relative to the housing while the piston assembly is within a narrower portion of a hydraulic cylinder. When the piston assembly reaches a larger diameter portion of the cylinder, the hydraulic fluid rushes past the piston assembly which allows a knocker connected to the spline mandrell to collide with the outer housing. A compression spring returns the piston assembly to its rest position abutting a shoulder on the outer housing. Provision is made for a valve to be inserted in the piston assembly so that the system can be temperature compensated and more desirable hydraulic fluids can be used.





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