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4 4 Hydraulic Hydraulic SystemSystem
As high-pressure oil from the main oil pump flows through the priority valve, it is As high-pressure oil from the main oil pump flows through the priority valve, it is divided betweendivided between
two circuits. One circuit runs via two circuits. One circuit runs via the multi-way valve. High-pressure oil from this multi-way valve isthe multi-way valve. High-pressure oil from this multi-way valve is
routed to the lift cylinder or tilt cylinder. When the slide valves of both the lift and tilt cylinders arerouted to the lift cylinder or tilt cylinder. When the slide valves of both the lift and tilt cylinders are
in the neutral position, no oil is supplied by the priority valve. When the lift slide valve is pulled,in the neutral position, no oil is supplied by the priority valve. When the lift slide valve is pulled,
the high-pressure oil flows under the lift cylinder piston and pushes the piston rod upward. Whenthe high-pressure oil flows under the lift cylinder piston and pushes the piston rod upward. When
the lift slide valve is pushed, the bottom of the lift cylinder piston is changed to the low pressurethe lift slide valve is pushed, the bottom of the lift cylinder piston is changed to the low pressure
and relies on its own weight and the load weight to make the piston rod drop. At this point, oiland relies on its own weight and the load weight to make the piston rod drop. At this point, oil
flowing out of the lift cylinder and through the one-way speed limiting valve controls the loweringflowing out of the lift cylinder and through the one-way speed limiting valve controls the lowering
speed, and oil is not supplied by the priority valve. When the tilt slide valve is operated,speed, and oil is not supplied by the priority valve. When the tilt slide valve is operated,
high-pressure oil flows into a chamber of the tilt cylinder and the other side is changed to the lowhigh-pressure oil flows into a chamber of the tilt cylinder and the other side is changed to the low
pressure, thereby causing the mast to tilt forward or backward. The other circuit runs via thepressure, thereby causing the mast to tilt forward or backward. The other circuit runs via the
steering gearsteering gear, which is , which is prioritised to ensure operation of the prioritised to ensure operation of the steering system.steering system.
Main oil pumpMain oil pump
Fault Fault Possible Possible cause cause Corrective Corrective measuremeasure
Oil pump notOil pump not
pumping outpumping out
oiloil
Low Low oil oil tank tank level level TTop op up up to to specified specified oil oil levellevel
Clogged suction pipe or filterClogged suction pipe or filter
Flush oil circuit and oil tank. ChangeFlush oil circuit and oil tank. Change
hydraulic oil if dirtyhydraulic oil if dirty
Oil pumpOil pump
delivers oil atdelivers oil at
low pressurelow pressure
Worn Worn bearing; bearing; damaged damaged ring, ring, O-ring O-ring Replace Replace defective defective partsparts
Misadjusted Misadjusted safety safety valve valve Raise Raise the the pressure pressure with with a a pressure pressure gaugegauge
Air in the oil pumpAir in the oil pump
Tighten loose connectors on the suctionTighten loose connectors on the suction
sideside
Add hydraulic oil to the tankAdd hydraulic oil to the tank
Check pump oil sealsCheck pump oil seals
Wait for bubbles in oil tank to disappearWait for bubbles in oil tank to disappear
before using pumpbefore using pump
Oil pumpOil pump
noisynoisy
Cavitation generated by kinkedCavitation generated by kinked
suction-side hose or clogged filtersuction-side hose or clogged filter
Adjust or replace hose and clean filterAdjust or replace hose and clean filter
Air Air entering entering from from loosenedloosened
suction-side connectorssuction-side connectors
Re-tighten every connectorRe-tighten every connector
Cavitation caused by high viscosity ofCavitation caused by high viscosity of
hydraulic oilhydraulic oil
Replace with new hydraulic oil of viscosityReplace with new hydraulic oil of viscosity
suitable for the oil pump operating speedsuitable for the oil pump operating speed
Only work when oil temperature is normalOnly work when oil temperature is normal
Air bubbles in hydraulic oilAir bubbles in hydraulic oil
Check cause of bubbles, then takeCheck cause of bubbles, then take
appropriate stepsappropriate steps
Oil pumpOil pump
leaks oilleaks oil
Damaged pump oil seal, damagedDamaged pump oil seal, damaged
O-ring or sliding surfaces of oil pumpO-ring or sliding surfaces of oil pump
wornworn
Replace defective partsReplace defective parts
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