Hitachi ZW 120-6 Operator's Manual page 258

IMPORTANT:
 When connecting hydraulic hoses and pipes, take
special care to keep seal surfaces free from dirt and
to avoid damaging them. Keep these precautions in
mind.
 Wash hoses, pipes, and the tank interior with a
washing liquid and thoroughly wipe it out before
reconnecting them.
 Only use O-rings that are free of damage or defects.
Be careful not to damage them during reassembly.
 Do not allow high pressure hoses to twist when
connecting them. The life of twisted hoses will be
shortened considerably.
 Carefully tighten low pressure hose clamps. Do not
overtighten them.
 When adding hydraulic oil, always use the same
brand of oil; do not mix brands of oil. As the machine
is filled with Super EX 46HN when it is shipped from
the factory, use it as a general rule. When selecting
to use another brand of oil listed in the table "Brand
names of recommended hydraulic oil", be sure to
completely replace the oil in the system.
 Do not use hydraulic oils other than those listed in
the table "Brand names of recommended hydraulic
oil".
 Never run the engine without oil in the hydraulic oil
tank.
MAINTENANCE
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