H Y D R A U L I C S Y S T E M
S Y S T E M S O P E R A T I O N
open center valve with two valve spools: one for
bucket lift and lower, and one for bucket tilt back
and dump. The oil from the pilot system causes
movement of the valve spools. When the valve
spools are in HOLD position, the oil goes through
lift and tilt control valve (7) and back to the hy-
The tilt valve spool has three positions: TILT
BACK, HOLD and DUMP. When moved to an
operating position, the tilt valve spool sends oil to
tilt cylinder (4). The lift valve spool has four posi-
tions: RAISE, HOLD, LOWER and FLOAT.
When moved to an operating position, the lift valve
spool sends oil to lift cylinder (6). The implement
section oil goes first to the tilt valve spool and then
to the lift valve spool. When the tilt valve spool is
fully in TILT BACK or DUMP position, no pres-
sure oil goes to the lift valve spool and the lift cir-
cuit will not operate. Both lift and tilt circuits have
load check valves. Make-up valves are in the tilt
and lift rod end cylinder lines. The make-up valve
for the rod end of the lift cylinders is a vented valve.
The lower stem of lift and tilt pilot valve (3) releases
(vents) pressure in the spring passage of the rod
end lift make-up valve to provide the FLOAT oper-
ation. Main pressure relief valve (16) is in the im-
plement oil system before the tilt valve spool. Tilt
cylinder relief valves (17) and (18) are in both rod
end and head end lines. All of the load check valves,
make-up valves and relief valves are part of lift
and tilt control valve (7).
R I G H T S I D E O F M A C H I N E
5. Hydraulic tank. 19. Oil filters.
The flow of oil from the implement pump section
changes when the machine has an attachment
(three spool) control valve. The attachment control
valve has a lift valve spool, a tilt valve spool and
an attachment (third) valve spool. The operation
of this valve is very similar to lift and tilt control
valve (7). The pilot system oil from an attachment
(third) pilot valve causes movement of the attach-
ment valve spool. This valve spool is also an open
center type so that when all three valve spools are
in HOLD position, the oil goes through the attach-
ment control valve and back to the tank.
The attachment valve spool has three positions:
OPEN or RAISE, HOLD and CLOSE or LOWER.
When moved to an operating position, the valve
spool sends oil to the attachment cylinder(s). The
implement section oil now goes first to the attach-
ment valve spool before it gets to the tilt valve spool.
When the attachment valve spool is fully in CLOSE
or LOWER position, the tilt and lift circuits can
still operate. In this position, oil from the rod end
of the attachment cylinder(s) goes to the tilt and
lift valve spools. The shuttle valve and sequence
valve in the attachment circuit let the lift and tilt
circuits operate during CLOSE or LOWER opera-
tion. When the attachment valve spool is fully in
OPEN or RAISE position, no pressure oil goes to
the tilt valve spool and the tilt and lift circuits will
not operate. The attachment circuit has a load
check valve. In this attachment control valve, main
relief valve (16) is moved (relocated) so that it is
before the attachment valve spool in the system.
Attachment relief valves are in both rod end and
head end lines. These valves are also part of the
attachment control valve.
In operation with the tilt hydraulic circuit is the
bucket positioner (tilt kickout). It consists of tilt
detent lever (12), a roller and linkage, bucket posi-
tioner solenoid (15), a magnet and bucket positioner
switch (20). The bucket positioner moves tilt con-
trol lever (9) from the detent [on lever (12)] in TILT
BACK position to the HOLD position. This hap-
pens as the bucket moves from dump to tilt back
when it gets to the correct digging angle.
F R O N T O F T I L T C Y L I N D E R
20. Bucket positioner switch.