Komatsu Galeo PC800-8 Shop Manual page 200

SEN00384-02
Operation when oil is supplied
• When the travel lever is operated, the pressu-
rized oil from the control valve is supplied to port
P1. It pushes open check valve (5a) and flows
from motor inlet port M1 to motor outlet port M2.
However, the motor outlet port is closed by
check valve (5b) and spool (3), so the pressure
at the supply side rises.
• The pressurized oil at the supply side flows from
orifice a in spool (3) to chamber A. When the
pressure in chamber A goes above the spool
switching pressure, spool (3) is pushed to the
left.
As a result, port M2 and port P2 are connected,
the outlet port side of the motor is opened, and
the motor starts to rotate.
Operation of brake when traveling downhill
• If the machine tries to run away when traveling
downhill, the motor will turn under no load, so the
pressure at the motor inlet port will drop, and the
pressure in chamber A through orifice a will also
drop.
When the pressure in chamber A drops below
the spool switching pressure, spool (3) is
returned to the right by spring (2), and outlet port
M2 is throttled.
As a result, the pressure at the outlet port side
rises, resistance is generated to the rotation of
the motor, and this prevents the machine from
running away.
In other words, spool (3) moves to a position
where the pressure at outlet port M2 balances
the pressure at the inlet port and the force gen-
erated by the weight of the machine. It throttles
the outlet port circuit and controls the travel
speed according to the amount of oil discharged
from the pump.
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10 Structure, function and maintenance standard
PC800, 850-8