Idling-Proof Mechanism; Sealed And Dustproof Construction - Hitachi H 25PV Technical Data And Service Manual

8-2. Idling-proof Mechanism

When the tool is released from the concrete surface, sleeve (A) and the second hammer are forcibly moved to the
position illustrated in Fig. 4 by spring (A), 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.
Forward movement of
second hammer and striker

8-3. Sealed and Dustproof Construction

The cylinder case and crank case are sealed by three o-rings and an oil seal which serve to prevent leakage of
the grease, as well as to prevent dust and dirt from entering the mechanism. (Fig. 5)
Front cap
O-ring
Second hammer
O-ring
Cylinder case
O-ring
Spring (A)
Air chamber
Slide sleeve (A)
Fig. 4
O-ring
Fig. 5
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Air hole
O-ring
Crank
Oil seal