System Will Not Operate in Either Direction
Item
Description
Action
Oil level in reservoir.
Insufficient hydraulic fluid to supply system loop.
Fill reservoir to proper level.
Pump control orifices
Control orifices are blocked.
Clean control orifices.
Pump control screens
Control screens are blocked.
Replace control screens. Only a Danfoss Authorized Service
Center may remove the unit’s endcap without voiding the
warranty.
Bypass function open
If bypass function is open, the system loop will be
depressurized.
Close bypass valves. Replace high pressure relief valve if
defective.
Low charge pressure with
pump in neutral
Low charge pressure insufficient to recharge system loop.
Measure charge pressure with the pump in neutral. If
pressure is low, go to Pump charge relief valve.
Low charge pressure with
pump in stroke
Low charge pressure resulting from elevated loop leakage.
Insufficient control pressure to hold pump in stroke.
Deadhead the pump to isolate it from the motor.With
pump in partial stroke and engaged for only a few seconds,
check pump charge pressure. Low charge pressure
indicates a malfunctioning pump. Continue to next step.
Good charge pressure indicates a malfunctioning motor or
other system component. Check motor charge relief
operation (if present).
Pump charge relief valve
A pump charge relief valve that is leaky, contaminated, or
set too low will depressurize the system.
Adjust or replace pump charge relief valve as necessary.
Charge pump inlet filter
A clogged filter will under supply system loop.
Inspect filter and replace if necessary.
Charge pump
A malfunctioning charge pump will provide insufficient
charge flow.
Repair or replace the charge pump.
System pressure
Low system pressure does not provide enough power to
move load.
Measure system pressure. Continue to next step.
High pressure relief or
pressure limiter valves
Defective high pressure relief or pressure limiter valves
cause system pressure to be low.
Repair or replace high pressure relief or pressure limiter
valves.
Input to control
Input operating improperly
Repair/replace control.
System Noise or Vibration
Item
Description
Action
Reservoir oil level
Low oil level leads to cavitation.
Fill reservoir.
Aeration of the oil/pump
inlet vacuum
Air in system decreases efficiency of units and controls.
Excessive noise, foaming oil, and hot oil all indicate air in
system.
Find location where air is entering into the system and
repair. Check that inlet line is not restricted and is proper
size.
Cold oil
If oil is cold, it may be too viscous for proper function and
pump cavitates.
Allow the oil to warm up to its normal operating
temperature with engine at idle speed.
Pump inlet vacuum
High inlet vacuum causes noise/cavitation.
Check that inlet line is not restricted and is of proper size.
Check filter and bypass switch.
Shaft couplings
A loose shaft coupling will cause excessive noise.
Replace loose shaft coupling..
Shaft alignment
Misaligned shafts create noise.
Align shafts.
Charge/system relief valves
Unusual noise may indicate sticking valves and possible
contamination.
Clean/replace valves and test pump.
Sluggish System Response
Item
Description
Action
Oil level in reservoir
Low oil level causes sluggish response.
Fill reservoir.
High pressure relief valves/
pressure limiter settings
Incorrect pressure settings affects system reaction time.
Adjust or replace high pressure relief valves.
Service Manual
H1P 069—H1P 250 Axial Piston Single Pumps
Troubleshooting
32 |
©
Danfoss | September 2020
AX152886482551en-000504
