Hitachi DH 30PC2 Technical Data And Service Manual page 17

Front cap
Grip
Key rail
Retainer
sleeve
Steel ball
Mechanism to prevent idle hammering
When the working tool is released from the workpiece, slide sleeve (A) and the second hammer are forcibly
moved to the position illustrated in Fig. 4 by clutch spring, and the striker moves out of striking position. When
this occurs, the air holes located at the position unaffected by the rebound of the striker at no load are opened
and the pressure within the air chamber remains unchanged even though the piston continues to reciprocate,
thereby preventing striking operation.
Second hammer
Moving distance of second
hammer and striker
Second
Striker
hammer
Air
Cylinder chamber
O-ring
Needle pin
Second gear
Bevel pinion
Armature
Slide sleeve (B)
Slide ring
Connecting rod
Clutch
Piston
Bevel
gear
Fig. 3
Slide sleeve (A)
Striker
Fig. 4
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Crank shaft
First gear
Clutch spring
Air chamber
Air hole