Abstract: The present invention utilizes a combined dual piston and cylinder arrangement surrounded by a sleeve all mounted within a container which is in turn placed within a drill collar. The pressure of the drilling mud within the drill string drives the pressure pump of the present invention by forcing the piston up and down. Stops on the piston rod maneuver a sleeve which opens and closes inlets and outlets so that the desired flow can be obtained to drive the cylinder, piston and rod arrangement up and down. When the pistons are driven downward, drilling mud is forced through a conduit into a drill bit and out a jet nozzle at a high pressure so as to facilitate the fracturing and removal of the formation being drilled.