Drive for a pneumatic hammer

In a pneumatic drive for a hammer tool including a cylinder;

• a piston slidably received in the cylinder and dividing the inner space of the cylinder into two cylinder chambers;
• a drive output member formed as a piston rod attached to the piston and projecting from the cylinder;
• a pressure-responsive valve means for admitting compressed air alternately to the cylinder chambers;
• means defining discharge openings in the cylinder wall for releasing compressed air alternately from the cylinder chambers dependent upon the position of said piston with respect to the discharge openings;
• the improvement wherein said discharge openings consist of a plurality of spaced, serially arranged cylindrical ports each having a diameter that equals at least one half of the height of said piston measured in the direction of its reciprocation and means defining a first expansion chamber directly communicating with said cylindrical ports and two second expansion chambers each communicating directly with said first expansion chamber.