Yanmar EF-494T - Control valve; Relief valve

9 HYDRAULIC LIFT UNIT 9 HYDRAULIC LIFT UNIT
EF494T TM 06/2011 edition
182
9.1.3 Control valve
Operate the spool according to the control lever
position to allow the lift arm to be put in the
"neutral," "up" or "down" position.
(1) Unload valve
Prevents the oil temperature from rising
excessively.
(2) Flow control valve
Reduces shock when the lift arm is at its
highest position.
(3) Mechanical check valve
Prevents the implement from being
lowered. This valve allows oil to escape
from the cylinder when the lift arm is in the
"down" position.
(4) Load check valve
Prevents back flow.
(5) Main spool
Switches between the circuits used for
changing the lift arm positions ("neutral,"
"up," and "down").
9.1.4 Relief valve
If the pressure in the hydraulic circuit becomes
excessively high, this valve will open to allow oil
to escape to the tank.
The pressure setting of the valve can be adjusted
by increasing or decreasing the size of shims.
Relief pressure setting:
16.7±17.4 MPa (170-178 kgf/cm
2
)
(A) From the hydraulic pump
(B) To the tank
(C) Pressure adjustment shims
(D) Relief valve mechanism