Percussive drill with noise silencer

Claim 1

A SOUND FILTERING UNIT FOR USE IN COMBINATION WITH A PNEUMATIC PERCUSSIVE TOOL OF A TYPE HAVING A CYLINDRICAL PORTION, A RADIAL RIB LENGTHWISE OF THE CYLINDRICAL PORTION, AND A PAIR OF SPENT AIR EXHAUST PORTS EACH OPENING IN IDENTICAL MANNER THROUGH AN OPPOSITE FACE OF THE RADIAL RIB, THE SOUND FILTERING UNIT COMPRISING A PAIR OF IDENTICAL CASTING HALF-SECTIONS EACH ADAPTED TO OVERLIE AN OPPOSED SURFACE AREA OF THE RADIAL RIB AND CYLINDRICAL PORTION OF THE TOOL AND ADAPTED TO BE WELDED TO EACH OTHER AND TO THE SURFACE OF THE TOOL, THE SOUND FILTERING UNIT HAVING A PAIR OF OPPOSED LONGITUDINALLY EXTENDING OPENINGS EACH ADAPTED TO OVERLIE ONE OF THE SIDES OF THE RIB OVER ONE OF THE EXHAUST PORTS, A GROUP OF UPPER CHAMBERS, A GROUP OF LOWER CHAMBERS, SEPARATE INTERMEDIATE THROAT MEANS CONNECTING EACH UPPER CHAMBER WITH A SEPARATE LOWER CHAMBER, A SEPARATE DISCHARGE THROAT MEANS CONNECTED TO EACH LOWER CHAMBER, AN ARCUATE OPENING IN THE FILTERING UNIT OVERHEAD OF THE UPPER CHAMBERS ADAPTED TO OVERLIE OPPOSITE SIDES OF THE RIB AND THE CYLINDRICAL PORTION OF THE TOOL, THE ARCUATE OPENING MERGING AT OPPOSITE ENDS WITH THE LONGITUDINALLY EXTENDING OPENINGS, AND SEPARATE INLET THROAT MEANS CONNECTING EACH UPPER CHAMBER WITH THE OVERHEAD OPENING.