Fluid accelerator for use with an hydraulic jar in a well

Claim 1

An accelerator for use with a hydraulic jar in a well, comprising: a. an outer housing; b. a hollow mandrel disposed in said housing and slidable relative thereto; c. the exterior of said mandrel being spaced from the interior of said housing to form an annular chamber therebetween; an upper seal between said mandrel and said housing at the upper end of said chamber; e. a lower seal between said mandrel and said housing at the lower end of said chamber; f. a piston mounted on said mandrel for longitudinal movement relative thereto and disposed in said chamber between said upper seal and said lower seal; g. compressible liquid in said chamber adapted to be compressed on one side of said piston during relative movement of said piston in one longitudinal direction with respect to said housing; h. means for transferring liquid in said chamber from the other side of said piston to said one side thereof upon a relative movement of said piston in the other longitudinal direction with respect to said housing; h. means on said mandrel and engageable with said piston for limiting longitudinal movement of said piston relative to said mandrel between a first position and a second position; i. said piston and said mandrel having passage means associated therewith for establishing fluid flow from one side of said piston to the other when said piston is in said first position; and j. means on said mandrel engageable with said piston for closing off fluid flow through said passage means when said piston is in said second position for compressing the liquid as said piston and mandrel move in said one longitudinal direction relative to said housing.