Komatsu PC200-8M0 Shop Manual page 217

403 Hydraulic system, Part 3
Travel motor
Brake valve
The brake valve consists of suction safety
q
valve (18A) and counterbalance valve (18).
q Functions and operations of respective compo-
nents shall conform to the following.
1) Counterbalance valve and check valve
Function
q When traveling downhill, the machine travel
speed tends to get faster than the motor
(engine) speed because of the downward force
generated from its own weight.
q If the machine travels with the engine at low
speed, the motor may rotate without load,
causing the machine to run away; resulting in a
very dangerous situation.
These valves are used to prevent above by
q
controlling the machine to travel according to
the engine speed (pump discharge).
PC200, 200LC, 220, 220LC-8M0
Operation when pressurized oil is supplied
q Operating the travel lever conducts the pres-
surized oil from the control valve to port (PA).
The pressurized oil push-opens suction safety
q
valve (18A) and then flows to motor outlet port
(MB) through motor inlet port (MA).
q The motor outlet side is closed by suction
safety valve (18B) and spool (19), so the pres-
sure at the supply side rises.
SEN06121-00
19
10-403