Hitachi DH 40SR Service Manual And Technical Data page 17

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 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.
Moving distance of the second hammer and the striker
Shock-absorbing mechanism
At the instance of releasing the working tool from the workpiece by moving the main body up, the second
hammer contacts driver as shown in Fig. 5 then the cushion (damper (B)) provided between driver holder and
front cover absorbs the striking force of the second hammer. Thus the durability of the Model DH 40SR is
increased greatly because the second hammer does not strike the tool retainer directly.
Driver holder
Front cover
Driver
Damper (B)
Second hammer
Slide ring
Second hammer
Slide sleeve (A)
Striker
Fig. 4
Fig. 5
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Sleeve (A)
Air chamber
Spring (A)
Air hole