Patent ID: 7383894

Claim:
A pneumatic hammer drill, comprising: a handle body; a pneumatic cylinder having a cylinder rear end fitted in said handle body, a front tool-connecting end, an air passage, and a pressure chamber; an air valve fitted in said handle body adjacent to said cylinder rear end, and having a front bearing end, a valve orifice interconnecting fluidly said air passage and said pressure chamber, an opening disposed at said front bearing end in communication with said valve orifice, and a diaphragm disposed across said valve orifice; a piston disposed slidably in said pressure chamber and having a piston rear end capable of moving toward or away from said front bearing end; and an air trap arrangement associated with said piston rear end and said front bearing end to trap air between said piston rear end and said front bearing end and around said opening so as to provide a shock-absorbing air cushion when said piston rear end moves towards said front bearing end, said air trap arrangement including a protrusion formed in one of said front bearing end and said piston rear end, and a cavity formed in the other one of said front bearing end and said piston rear end to receive said protrusion, said protrusion having a cross section smaller than that of said cavity; said air valve further including front and rear valve casings, said front valve casing being provided with said front bearing end and having an annular groove extending continuously in said front bearing end and around said protrusion and said cavity, and an aperture formed in the groove in front of said valve casing and communicated fluidly with said valve orifice, wherein said aperture is open to said annular groove so as to communicate with said annular groove; and wherein said air passage has a rear end aligned with a portion of said annular groove and communicated fluidly with said annular groove which fluidly connects said air passage to said aperture.