Abstract: A downhole circulation sub or valve (105) includes a tubular housing with an outer port (140) and a valve piston (170) slidably disposed in the housing. A primary fluid flow path (130) extends through an inner flow bore of the housing and valve piston. In a first position, the valve piston isolates the outer port to prevent fluid communication between the inner flow bore and a well bore annulus. In a second position, the valve piston is moved to obstruct the inner flow bore and expose the outer port to the inner flow bore and allow fluid communication between the inner flow bore and the well bore annulus. An indexing mechanism (165) is coupled between the housing and the valve piston to guide the valve piston between the first and second positions. In some embodiments, the indexing mechanism includes a rotatable component (175).

Abstract: A hydraulic jar for a drilling assembly is disclosed. In some embodiments, the hydraulic jar includes a tubular housing, a mandrel disposed in the housing, an annulus between the mandrel and the housing, and a pressure relief mechanism disposed in the annulus. The pressure relief mechanism generally divides the annulus into first and second portions. The pressure relief mechanism includes first and second annular members in engagement with one another when the pressure in the second annulus portion is less than a predetermined value and a fluid flow path between the first and second annulus portions. The fluid flow path has a first size when the pressure in the second annulus portion is less than the predetermined value, and a second size that is larger than the first size when the pressure in the second annulus portion becomes equal to or greater than the predetermined value.