During Return - Hitachi NR90GC - 3-1/2" Gas Powered Clipped Head Framing Nailer Technical Data And Service Manual

2) When the Trigger [98] is depressed, the
switch in the Trigger [98] contacts the end of
Switch Lever (B) [114] and turns on. Then the
spark plug in the combustion chamber
discharges (Fig. 6).
Fuel burns and a sudden expansion occurs.
The Piston [39] is lowered to drive nails
(Fig. 7).
When the Piston [39] passes the hole of the
Cylinder Ass'y [42], combustion gas is
partially released into the atmosphere
through the Lead Valve [45]. Because the
Lead Valve [45] is a nonreturn valve, no air
comes in the Cylinder Ass'y [42]. When the
Piston [39] contacts the Piston Bumper [40],
combustion of fuel is almost completed.

(3) During return

When the Trigger [98] is depressed, the Chamber
Lock Bar [100] at the bottom of the Trigger [98] is
positioned under the Chamber [24] to prevent the
Chamber [24] from lowering while the Trigger [98]
is depressed. The Chamber [24] is sealed by the
O-rings [15] and [36] to cut off the atmosphere
(Fig. 7). Because combustion gas is partially
released into the atmosphere through the Lead
Valve [45], the pressure of the upper portion of the
Piston [39] becomes lower than the atmospheric
pressure. The Piston [39] is returned to the initial
position by the pressure difference between the
upper portion and the lower portion of the Piston
[39].
Spark plug
Combustion
chamber
Piston [39]
Lead Valve [45]
Hole of Cylinder
Ass'y [42]
Piston Bumper [40]
O-ring [15]
O-ring [36]
Chamber [24]
Lead Valve
[45]
Piston [39]
--- 13 ---
Switch Lever
(B) [114]
Trigger
[98]
Nail
Fig. 6
Chamber Lock Bar [100]
Fig. 7
Switch