Hitachi ZW180 Operator's Manual page 244

MAINTENANCE
Bleed air from the hydraulic system.
After changing hydraulic oil or replacing the return filter,
pilot filter and/or suction filter, bleed air from the hydraulic
system following the procedures below:
Bleed air from the hydraulic circuit:
After supplying oil, start the engine. Move the bucket and
lift arm cylinders several times to bleed air mixed in the hy-
draulic circuit.
Rest the bucket on the ground to resume the hydraulic oil
level check position.
Stop the engine. Check the oil level. Add oil as needed.
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