Abstract: A percussion tool includes an actuating piston and a pump. The pump includes: a cam ring, a valve plate, a piston housing, and a piston. The cam ring includes an aperture having a camming surface. The valve plate faces the cam ring and includes a fluid port extending therethrough. The piston housing includes a fluid passage extending therethrough and is disposed within the aperture of the cam ring and rotates within the cam ring. A piston reciprocates within the piston housing. The fluid passage in the piston housing is configured to alternate between being in fluid communication with the fluid port in the valve plate and being isolated from the fluid port as the piston housing is rotated relative to the cam ring and valve plate. The flow port in the valve plate is larger in flow area than the flow area of the fluid passage in the piston housing.