Hitachi NR 65AK Service Manual page 19

(3) During return: (Fig. 16 and Fig. 17)
1) When either Pushing Lever (A) [30] or Trigger
[52] is released, Plunger (A) [47] 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) [44], Valve Piston (B) [44] 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 (
air passage and flows into the head valve
chamber to push down Head Valve (A) [10].
As a result, Head Valve (A) [10] and Cylinder
[15] are sealed and, at the same time, Head
Valve (A) [10] and Exhaust Cover [5] are
released to open the exhaust vent.
4) The compressed air at the upper portion of
Piston (H) [17] is discharged into the
atmosphere through the exhaust vent. In this
way, the air pressure at the upper portion of
Piston (H) [17] is reduced, and the greater
pressure of the air accumulated in the return air
chamber pushes Piston (H) [17] upward.
5) If the air pressure at the lower portion of Piston
(H) [17] is higher than that of the atmosphere
after Piston (H) [17] has fully returned, the
excess air pressure is discharged into the
atmosphere through the clearance between the
Piston Bumper [19] and the driver blade.
) passes through the
--- 15 ---
Fig. 16
Fig. 17 Control valve section