Danfoss 51 Series Service Manual

Sluggish system
Check Cause Corrective action
1.
Control orifices Blocked or restricted orifice will cause sluggish
response. Orifices installed to the wrong locations
will cause PCOR control to be sluggish.
Remove, inspect and clean all orifices. Ensure the
appropriate orifices are installed.
2.
Threshold setting (proportional
controls)
Inappropriately high threshold setting will shift the
motor at the wrong time.
Check threshold setting. Adjust if necessary.
3.
Control spool or piston A sticky 4-way spool or control piston will cause
sluggish response.
Clean and inspect the 4-way valve spool and control
piston. Replace if necessary.
4.
Pressure compensator setting Inappropriately low pressure compensating setting
will shift motor to maximum displacement at lower
pressure
Check pressure compensator setting. Adjust if
necessary.
5.
Control input signal An improper or erratic input signal to the control
may cause sluggish response.
Check input signal or electric current and correct if
necessary.
6.
Charge pressure Inappropriately low pressure setting at loop
flushing relief valve may cause improper supply
pressure to motor control.
Measure change pressure in forward and reverse.
Adjust loop flushing relief valve if necessary.
7.
System pressure Inappropriately low system pressure setting may
cause sluggish response.
Measure system pressure. Adjust pump pressure
limiter or system relief valve if necessary.
8.
Internal leakage Excessive leakage will cause lower charge pressure
and affect performance.
Install loop flushing defeat option and monitor case
flow. If case flow is excessive, motor may require major
repair. Contact your Danfoss service provider.
System operating hot
Check Cause Corrective action
1.
Oil level Insufficient hydraulic fluid will cause overheating. Fill reservoir to proper level.
2.
Heat exchanger Blocked heat exchanger or low air flow will not
sufficiently cool the system.
Check temperature upstream and downstream of heat
exchanger. Clean, repair, or replace heat exchanger if
necessary.
3.
Loop flushing charge pressure Inappropriately high loop flushing relief valve
setting will reduce or prevent loop flushing flow.
Improper orifice size will not give proper flow for
cooling purposes.
Monitor case drain flow. If low, adjust loop flushing
relief valve setting or replace with orificed type relief.
4.
System pressure If system relief valve settings are too low, excess
heat will be generated.
Adjust system relief valve settings.
5.
Air in system Entrained air generates heat under pressure and
causes cavitation
Look for foam or bubbles in reservoir. Check for leaks
on inlet side of charge pump.
6.
Internal leakage Excessive internal leakage will overheat the system. Install loop flushing defeat option and monitor case
flow. If case flow is excessive, motor may require major
repair. Contact your Danfoss service provider.
Excessive noise or vibration
Check Cause Corrective action
1.
Oil level in reservoir Insufficient hydraulic fluid will cause cavitation. Fill reservoir to proper level.
2.
Air in system Air bubbles may lead to cavitation. Look for foam or bubbles in reservoir. Check for leaks
on inlet side of charge pump.
3.
Shaft coupling Loose shaft coupling creates excess noise. Replace loose shaft coupling. Replace or repair motor
if shaft splines are worn excessively.
4.
Shaft alignment Misaligned shafts create excessive noise and
damage motor.
Correct shaft misalignment.
Service Manual
Series 51 and 51-1 Motors
Troubleshooting
©
Danfoss | March 2016 11008567 | AX00000013en-US0202 | 29

Danfoss 51 Series Specifications

General

Power Output	Unknown
Cylinders	Unknown
Fuel Type	Unknown
Cooling System	Unknown
Aspiration	Unknown