IV-86
HYDRAULIC UNITSSELF-LEVEL VALVE
OPERATION
This valve causes the bucket to tip forward as the lift
arms rise, ensuring that the bucket always remain
horizontal to the ground.
Self-Leveling Operation
<Arm Spool Out, Bucket Spool Neutral>
Oil ejected from the rod side of the arm cylinder (1)
flows into port A of the self-leveling valve, where
the difference in the area of adjust double orifice A1
(2) and fixed orifice A2 (3) causes the oil to split and
flow to ports D and B.
Relative flow: QD/QB = A1/A2
Oil ejected from port D then heads into the head side
of bucket cylinder (4), while oil ejected from port B
returns to the tank. When the pressure of the right
edge of rod spool (5) increases to the point where
it exceeds the force exerted by spring (6), the oil
which has been ejected from the rod side of bucket
cylinder (4) flows out of port B, coming out of port
C and passing along the surface of unloading spool
(5) before returning to the tank.
A portion of the oil which has thus run out from the
rod side of the arm cylinder will then enter the head
side of the bucket cylinder and cause the bucket to
tip forward as the arm rises, ensuring that the bucket
always remain horizontal to the ground while it di-
vides the flow of the oil.
Note that if, in self-leveling operation, bucket cylin-
der (4) reaches as far as the stroke end, then the head
side of bucket cylinder (4) will be blocked and the
oil run out of the port D side will then run through
the right-hand hole (7) of unloading spool (5), out of
port B, and back into the tank. This ensures that arm
cylinder (1) continues moving upward.
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