Danfoss 51 Series Service Manual

Motor operates normally in one direction only
Check Cause Corrective action
1.
Charge pressure If charge pressure is low in one direction, the loop
flushing shuttle spool may be sticking to one side.
Measure charge pressure in forward and reverse. If
pressure drops in one direction, inspect and repair
loop flushing shuttle spool.
2.
Motor control If control shifts motor to minimum displacement in
one direction, motor may not have enough torque
to operate.
Measure maximum and minimum servo pressures to
check control operation. Repair control or correct
input signal if necessary.
3.
Pressure compensator control If pressure compensator operates in one direction
only, the motor will stay at minimum displacement
in the other direction
Check brake pressure defeat spool. It may be sticking
or receiving an improper signal. Repair spool or
correct input signal.
Improper output speed
Check Cause Corrective action
1.
Oil level in reservoir Insufficient hydraulic fluid will reduce system
efficiency.
Fill reservoir to proper level.
2.
Threshold setting Improper threshold setting will cause motor to
have wrong displacement for given signal.
Check threshold setting. Refer to control service
manual for adjustment procedure.
3.
Pressure compensator setting Improper pressure compensator setting shifts
motor displacement at wrong pressure.
Check pressure compensator setting. Adjust if
necessary.
4.
Control spool or piston Pressure compensator piston or spool sticking
holds motor at wrong displacement.
Check pressure compensator piston or spool. Repair
or replace if needed.
5.
Control orifices Blocked or restricted orifice causes motor to shift
improperly.
Remove, inspect, and clean all orifices.
6.
Control piston Sticky control piston causes motor to shift
improperly.
Check control piston for proper operation. Repair if
necessary.
7.
Control input signal Improper input signal causes motor to shift
improperly.
Correct control input signal.
8.
Internal leakage Excess internal leakage causes lower charge
pressure and affects system performance including
output speed.
Install loop flushing defeat option and monitor case
flow. If case flow is excessive, motor may require major
repair. Contact your Danfoss Service Provider.
Low output torque
Check Cause Corrective action
1.
System pressure Low system pressure at motor reduces output
torque.
Measure system pressure at the motor. If the pressure
limiter or relief valve setting is low, increase setting to
the proper level.
2.
Charge pressure Low loop flushing relief valve setting may cause
improper supply pressure to motor control.
Measure charge pressure in forward and reverse.
Adjust loop flushing relief valve setting if necessary.
3.
Pressure compensator setting High pressure compensator setting causes
improper motor displacement for torque required.
Check and adjust pressure compensator setting.
4.
Control orifices Blocked or restricted orifice causes motor to shift
improperly.
Remove, inspect and clean all orifices.
5.
Pressure compensator piston or
spool
Sticking pressure compensator piston or spool
causes control to hold motor at minimum
displacement.
Remove and inspect control spool and sensing piston.
Repair or replace if necessary.
6.
Control spool or piston Sticking 4-way spool or control piston causes
motor to shift improperly.
Remove and inspect 4-way spool and control piston.
Repair or replace if necessary.
7.
Two position solenoid Two position control not shifting motor to
maximum displacement.
Inspect solenoid valve for bent stem or bad coil.
Repair or replace if necessary.
Service Manual
Series 51 and 51-1 Motors
Troubleshooting
30 |
©
Danfoss | March 2016 11008567 | AX00000013en-US0202

Danfoss 51 Series Specifications

General

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