Komatsu PC200-8M0 Shop Manual page 161

402 Hydraulic system, Part 2
Functions and operation by valve
Unload valve
1. LS circuit
2. Valve
3. Pump circuit
4. Tank circuit
5. Spring
Function
q When all control valves are at HOLD, this valve
serves to drain as same amount of oil as the
pump discharge with swash plate angle at the
minimum.
q The pump pressure becomes the pressure cor-
responding to the set load of spring (5) in the
valve (referred to as P1).
q Since LS pressure is drained from LS bypass
valve, LS pressure C tank pressure C 0 MPa {0
2
kg/cm }.
Operation
q Pressure of pump circuit (3) is received by the
end of valve (2).
q Since the control valve is in NEUTRAL posi-
tion, pressure of LS circuit (1) is 0 MPa {0 kg/
2
cm }.
q Pressurized oil of pump circuit (3) stops at
valve (2), and the pressure rises as no relief is
available.
If this pressure grows larger than the force of
q
spring (5), valve (2) moves to the left.
q Ports (b) and (c) are interconnected, and the
pump pressurized oil flows to tank circuit (4).
q The pressurized oil of LS circuit (1) passes
from orifice (a) through port (c) and is drained
to tank circuit (4).
When this valve is actuated, the LS pressure
q
becomes nearly equal to the tank pressure.
q Since the pump discharge pressure - LS circuit
pressure during unloading is larger than pump
LS control pressure, the signal is output to min-
imize the pump swash plate angle.
PC200, 200LC, 220, 220LC-8M0
q During operation (when a given work is done
within the discharge available with the mini-
mum swash plate angle), the discharge pres-
sure corresponding to the minimum pump
swash plate angle is set to LS pressure + P1
pressure.
q The LS differential pressure (dPLS) with the
swash plate angle at the minimum becomes
P1 pressure.
SEN06120-00
19
10-402