Manitowoc National Crane NBT30H-2, Service Manual

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2
National Crane
03-20-2019 Control # 613-06
2-7
NBT30H-2 SERVICE MANUAL HYDRAULIC SYSTEM
If the problem is two or three circuits, check each circuit
separately. After a circuit is checked, use caps or plugs to
remove that circuit from the system. Continue to next circuit
down the line until the problem is found. NOTE: Do not remove the main relief valve from the circuit.
The relief valve must be kept in the circuit to inhibit
damage to the pump and other components.
General Hydraulic System Troubleshooting
Table 2-1
Symptom Possible Cause Remedy
Noise (above normal)
Air in system.
Low oil supply.
Restriction in pump inlet line.
Dirty oil.
Loose clamps, vibration of hydraulic lines.
Dirt or foreign material in a relief valve.
Broken control valve spool.
Pump bearings worn.
With engine at low rpm, operate all control
functions several times to return the air to
atmosphere through the tank breather.
Add recommended oil.
Remove and clean inlet line to pump.
Change oil and filters. See “Hydraulic
Filter Replacement” on page 2-19.
Check and tighten.
Clean or replace the relief valve.
Replace the control valve section.
Replace the bearings or pump.
Slow operating speeds (All
functions)
Low engine rpm.
Air leak in pump inlet line.
Air in oil (foam in tank).
Leakage in the load sense relief valve.
Improper load sense relief valve setting.
Leakage in hydraulic swivel.
Control valve not fully actuated.
Improper primary pump pressure.
Faulty pump.
Increase engine rpm.
Tighten pump inlet line. Replace O-ring
inlet flange.
Check oil level, look for leaks in the
system.
Remove and clean or replace the relief
valve.
Check and adjust relief valve setting. See
“Hydraulic Pump” on page 2-11.
Replace seals on swivel shaft.
Check spool travel.
Check and adjust pump pressure settings.
See “Hydraulic Pump” on page 2-11.
Overhaul or replace pump.
No movement when system is
first started.
Low oil level.
Air or restriction in inlet line to pump.
Cold oil or wrong weight of oil.
Check and add oil.
Check and tighten inlet line. Clear
restriction.
Use correct oil, follow manual warming
procedure.
Loss of movement during
operation.
Low oil level.
Vacuum in hydraulic tank.
Restriction or leakage in the relief valve.
Broken hydraulic line.
Bad seal in hydraulic swivel.
Broken gear or shaft in pump. Check and add oil.
Clean tank filler/breather cap.
Clean or replace the relief valve.
Replace.
Replace seals.
Overhaul or replace.