Komatsu Galeo PC138US-8 Shop Manual page 131

10 Structure, function and maintenance standard
2. When signal current is very small
(coil is energized)
When a very small signal current flows to coil
q
(2), coil (2) is energized, and a propulsion force
is generated on the right side of plunger (7).
Rod (6) pushes spool (5) to the right, and pres-
q
surized oil flows from port (P) to port (C).
Pressure on port (C) increases and the force to
q
act on spool (5) surface and the spring load on
spring (4) become larger than the propulsion
force of plunger (7).
Spool (5) is pushed to the left, and port (P) is
q
shut off from port (C).
Port (C) and port (T) are connected.
q
Spool (5) moves up and down so that the pro-
q
pulsion force of plunger (7) may be balanced
with pressure of port (C) + spring load of spring
(4).
The circuit pressure between the EPC valve
q
and the PC valve is controlled in proportion to
the size of the signal current.
PC138US, USLC-8
3. When signal current is maximum
(coil is energized)
As the signal current flows to coil (2), coil (2) is
q
energized.
When this happens, the signal current is at its
q
maximum, so the propulsion force of plunger
(7) is also at its maximum.
Spool (5) is pushed toward right side by rod
q
(6).
The maximum volume of pressurized oil is
q
conducted from port (P) to port (C), increasing
the circuit pressure across EPC valve and PC
valve to the maximum level.
Since port (T) is closed, pressurized oil does
q
not flow to the tank.
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