Compressed-air-operated percussion mechanism

A pneumatic percussion mechanism comprising:

• a housing;
• a percussion body axially movable within the housing;
• a collar member extending from the percussion body;
• a balancing body having a cylindrical element with a radial hole therein, the cylindrical element being axially movable within the collar member to form an annular space therebetween;
• an operating chamber defined by the percussion body and the balancing body;
• means for urging the percussion body and the balancing body toward one another;
• a compressed air inlet passage connected to the operating chamber, so as to cause the percussion body and the balancing body to move away from one another;
• an O-ring surrounding the cylindrical element, the O-ring being positioned in an annular recess on the cylindrical element so that during a first portion of a stroke of the balancing body, the O-ring is contained within the collar member, and during a second portion of the stroke of the balancing body, the O-ring is not within the collar member;
• and
• an intermittently opening, primary valve device connected to the compressed air inlet passage to control a flow of the compressed air to the operating chamber;
• wherein when the compressed air is being supplied to the operating chamber and the balancing body is in the first portion of the stroke, the O-ring is expanded from a relaxed position by pressure of the compressed air provided though the radial hole in the cylindrical element to seal against an interior of the collar member, and when the balancing body is in the second portion of the stroke, the O-ring returns to the relaxed position and the compressed air is allowed to escape from the operating chamber thought the annular space;
• and
• wherein a maximum operational separation distance between the percussion body and the balancing body is defined by the position of the O-ring with respect to the collar member.