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
LIFT AND TILT CONTROL VALVE
(Lift Valve Spool in LOWER and FLOAT; Tilt Valve Spool in HOLD; Make-up Valve Vented)
10. Inlet passage for
16. Lift valve spool.
17. Chamber for pilot oil.
11. Tilt valve spool.
19. Make-up valve for rod
end of lift cylinders.
15. Outlet passage to
20. Vent passage to lift and
tilt pilot valve.
Load Check Valves
Load check valves (9) and (25) prevent reverse oil
flow in the cylinders (tilt and lift), which can cause
cylinder drift. For example, when the tilt valve spool
is in TILT BACK position, pump oil opens load
check valve (9) and goes through passages (6) and
(7) to the head end of the tilt cylinder. If the pressure
at inlet passage (10) decreases, the pressure of the
oil, along with spring (8) will close load check valve
(9) and hold the oil in the head end of the tilt cy-
linder, This prevents any movement of the tilt cy-
linder and will not permit the bucket to dump.
There are two make-up valves in the lift and tilt
control valve. Make-up valve (19) is in the rod end of
the lift circuit and make-up valve (4) is in the rod end
of the tilt circuit. The make-up valves will permit oil
22. Passage to rod end of
25. Load check valve for lift
23. Passage to head end of
from the return line to add with pump oil when the
cylinder rods are retracted faster than the pump can
supply oil to the cylinders. The make-up valves make
sure that there is enough oil available so that there is
no cavitation (vacuum) in the cylinders.
Make-up valve (4) operates when the rod end of
the tilt cylinder is retracted fast when the bucket is
dumped. When the pressure in passage (5) decreases
enough, the pressure in passage (13) will become
greater than the force of spring (3). Make-up valve
(4) will move up and oil from passage (13) will go
into passage (5) and add to the oil in the rod end of
the tilt cylinder. Make-up valve (4) will operate in
the same way when an outside force on the bucket
causes the tilt cylinder to be retracted.
During LOWER operation, make-up valve (19)
operates-the same way as make-up valve (4). During
FLOAT operation, make-up valve ( 19) provides the
float operation of the lift circuit (see FLOAT