Hitachi NR 90AC3, Technical Data And Service Manual

Page: 16 / 39

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(3) During return (See Fig. 7 and Fig. 8.)
1) When either Pushing Lever (A) [37] or Trigger (A)
[47] is released, Plunger (A) [61] goes down and
the compressed air in the accumulator flows into
the valve piston lower chamber.
2) As the air pressure in the valve piston lower
chamber increases to overcome the air pressure
applied on the upper portion of Valve Piston (B)
[57], Valve Piston (B) [57] is forced upward. When
this occurs, the exhaust valve is closed and the air
supply vent is opened.
3) When the air supply vent opens, the compressed
air in the accumulator ( portion) passes
through the air passage and flows into the head
valve chamber to push down the Head Valve [10].
As a result, the Head Valve [10] and the Cylinder
[17] are sealed and, at the same time, the Head
Valve [10] and the Exhaust Valve Rubber [7]
separate to open the exhaust vent.
4) The compressed air above the Piston [19] is
discharged into the atmosphere through the
exhaust vent. In this way, the air pressure above
the Piston [19] is reduced, and the greater
pressure of the air accumulated in the return air
chamber pushes the Piston [19] upward.
5) If the air pressure below the Piston [19] is higher
than that of the atmosphere after the Piston [19]
has fully returned, the excess air pressure is
discharged into the atmosphere through the
clearance between Piston Bumper (B) [25] and
the driver blade.
Fig. 8 Control valve section
Fig. 7
Head valve chamber
Air passage
Control
valve
section
Piston Bumper
(A) [24]
Head Valve [10]
Exhaust vent
Exhaust Valve Rubber [7]
Return air
chamber
Piston Bumper
(B) [25]
Driver blade
Pushing Lever (A)
[37]
Piston [19]
Accumulator
Trigger (A) [47]
To the head valve chamber
Plunger (A) [61]
Valve
Piston (B) [57]
Valve piston
lower chamber
Exhaust
valve
Air passage
Accumulator
Air supply vent
Cylinder [17]