31 - 13
Operation (cont’d)
Relief valve
1. Main Relief Valve (Refer to Fig. 1, 2, 11).
The oil from port 5P pushes up the check valve (26) passes
through the 5-spool parallel passage (B) and passage (18)
which connects to the inlet passage (19) to the relief valve.
The oil from port 4P actuates the check valve (25) through
the 4-spool neutral passage (a) and connects the inlet
passage (19) of the relief valve, with the main relief valve.
This prevents the maximum pressure from ports 4P and 5P
from exceeding the set pressure.
2. Overload Relief Valve (Refer to Fig. 1, 2, 11).
The over load relief valves are set in each cylinder port of
boom 1, arm 1 and the bucket to prevent abnormally high
pressure on the actuator from outside forces.
The maximum pressure can be regulated if the set pressure
becomes lower than the main relief valve.
If the cylinder pressure becomes negative, the relief valve
functions to absorb the oil from the tank and to prevent
cavitation.
Section E Hydraulics
9803/6020
Section E
31 - 13
Issue 1
Control Valve
Fig. 11
289840
A
B
C
A Tank Passage Ta
B Poppet (26)
C Poppet (25)
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