-13-
A - A
A
A
Air passage
(Outside the
gear cover)
Felt packing (B)
Valve
Felt packing (A)
(Inside the Gear cover)
Inner cover
Fig. 5
Internal pressure adjustment mechanism
An air passage is provided as shown in Fig. 5 to let out air inside the gear cover and let outside air in the
gear cover. This passage is sandwiched between felt packings to pass only air (pressure). As a result,
fluctuations in internal pressure are minimized for stable hammering operation and preventing grease
leakage.
Slip mechanism
The slip mechanism in the Model DH 22PH consists of a coil spring that applies a pre-set amount of
pressure to ensure the interlocking of three claws provided on the flange of the cylinder (i.e., final
rotating shaft) and the matching claws provided on the face of the second gear, which transmits rotation
to the cylinder. The second gear is fitted to the cylinder with a certain amount of play. If excessively large
torque is applied to the tool shaft (cylinder), the force of the torque will exceed the coil spring pressure
and cause the claws on the second gear to disengage from and ride over the claws on the cylinder;
therefore, the second gear remains idle and does not transmit rotation. Even if the drill bit comes into
contact with a reinforcing bar within the concrete, causing sudden excessive torque, the slip mechanism
functions to prevent damage to the gears and possible loss of tool control by the operator (slip torque
setting applied to the tool shaft: 1.0 to 2.0 kgm).
Sealed and dust-proof construction
The gear cover is totally enclosed by oil seals, O-rings and other devices to prevent lubricating grease
from leaking, and keep dust and dirt out of the internal mechanisms. The drill bit chuck portion is
protected by a rubber front cap to keep out dust and chips that could cause improper drill bit fitting
and/or other faulty operation of the chuck section. The speed control switch is also fully dust-proof to
prevent dust and chips from entering the handle section and causing possible operational trouble or
insulation breakdown.
Speed control
The Model DH 22PH is equipped with a variable speed control switch that lets you freely select the
rotation speed and hammering force. When drilling into fragile materials, pull the switch trigger gently for
low rotation speed (hammering force) to achieve optimum results. Note that the switch trigger can only
be pulled halfway in reverse drilling, at a speed about half of that in forward drilling. In addition, the
switch stopper cannot be used in reverse drilling.
