Patent ID: 7814995

Claim:
A hydraulic jar for a drilling assembly, comprising: a tubular housing; a mandrel disposed in the housing; an annulus between the mandrel and the housing; a pressure relief mechanism disposed in the annulus and generally dividing the annulus into first and second portions, the pressure relief mechanism comprising: a first annular member having a first face; a second annular member having a second face, wherein the second annular member is translatable relative to the first annular member between an engaged position in which the faces are engaged and a disengaged position in which the faces are spaced apart; a groove in at least one of the first and second faces, the groove providing fluid communication between the first and second portions of the annulus; and a fluid flow path extending between the first and second portions of the annulus, the fluid flow path having a first size when the fluid pressure in the first portion of the annulus is less than a predetermined value, and having a second size that is larger than the first size when the fluid pressure in the first portion of the annulus is equal to or greater than the predetermined value.