Komatsu Galeo PC138US-8 Shop Manual page 200

SEN02550-01
2) When signal current is very small
(coil is energized)
When a very small signal current flows to coil
q
(5), coil (5) is energized, and a propulsion force
is generated on the left side of plunger (6).
Push pin (4) pushes spool (2) to the left, and
q
pressurized oil flows from port (P) to port (C).
Pressures on port (C) increases and the force
q
to act on surface (a) of spool (2) and the spring
load on spring (3) become larger than the pro-
pulsion force of plunger (6).
Spool (2) is pushed to the right, port (P) is shut
q
off from port (C) and ports (C) and (T) are con-
nected.
Spool (2) moves up and down so that the pro-
q
pulsion force of plunger (6) may be balanced
with pressure of port (C) + spring load of spring
(3).
The circuit pressure between the EPC valve
q
and the control valve is controlled in proportion
to the size of the signal current.
18
10 Structure, function and maintenance standard
3) When signal current is maximum
(coil is energized)
As the signal current flows to coil (5), coil (5) is
q
energized.
When this happens, the signal current is at its
q
maximum, so the propulsion force of plunger
(6) is also at its maximum.
Spool (2) is pushed to the left by push pin (4).
q
The maximum volume of pressurized oil is
q
conducted from port (P) to port (C), increasing
the circuit pressure across EPC valve and the
control valve to the maximum level.
Since port (T) is closed, pressurized oil does
q
not flow to the hydraulic tank.
PC138US, USLC-8