Abstract: A fluid operated impact drilling tool has a hammer slidably mounted in a casing connected to a string of drilling pipe. Inside the casing above the hammer is mounted a valve. Both the valve and hammer have reciprocal sliding movement along the longitudinal axis of the tool to substantially interrupt flow of a drilling fluid therethrough. Movement of the valve and hammer predominantly results from different pressures acting on separate pressure areas of the valve and hammer. The hammer may impact either an anvil or a bit attached thereto. Wear on the valve and hammer is reduced by smooth, hardened surfaces at locations subject to wear. A trapped fluid may also be used in an alternative embodiment to dampen the shock effect of the valve as it reaches its upper and lower stops.

Abstract: A fluid operated impact drilling device wherein a hammer is mounted in a casing for axial reciprocating movement and drilling fluid flows through the hammer. The flow of drilling fluid is controlled by a valve element at the upper portion of the hammer. Differential pressure areas are provided in the flow path of the drilling fluid which coupled with the action of the valve element causes the hammer to be repeatedly lifted up into the valve element and then driven downward against an anvil by the force of the drilling mud. The valve element remains partly open, thereby preventing excessive backpressures from damaging the drill pipe or equipment. The drilling device is attached immediately above the drill bit with the drill bit being secured to the anvil. A catcher device is mounted to stop the reciprocating impact action of the hammer against the anvil upon picking the bit up off bottom.