Abstract: A pressure converter for mounting above the drill bit on a drill pipe for generating a higher fluid pressure in a portion of a drilling fluid flow, comprises a piston moveable in a cylinder. The piston has a large piston area and an opposite small piston area, which provides an increased pressure in a smaller portion of the drilling fluid flow. A valve arrangement controls the drilling fluid flow to and from the cylinder. A high pressure conduit with a check valve connects the space in front of the small piston area to a header conduit for drilling fluid at the increased pressure. The piston also has another large piston area facing oppositely of the first large piston area and being adapted to be influenced by the drilling fluid pressure in the drill pipe so as to move the piston in an opposite direction. Another small piston area facing oppositely of the first small piston area, is adapted to provide an increased drilling fluid pressure upon piston movement in the opposite direction.