Cause
Problem
Solution
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.
Isolate pump from motor by blocking system ports. 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, or contaminated, or set
too low will depressurize the system.
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
valves
Defective high pressure relief valves cause system pressure to
be low
Replace high pressure relief valves.
Control Linkage
Linkage operating improperly
Repair/replace control linkage
DDC20/24 sluggish system response
Cause
Problem
Solution
Oil level in reservoir Low oil level causes slower system response
Fill reservoir
High pressure relief
valves
Incorrect system pressures will affect system reaction time. High
pressure relief valve with orifice may affect system reaction
time.
Replace high pressure relief valves
Low prime mover
speed
Low engine speed will reduce system performance
Adjust engine speed
Air in system
Air in system will produce slower system response
Fill tank to proper level. Cycle system slowly for several minutes
to remove air from system
Pump inlet vacuum Inlet vacuum is too high resulting in reduced system pressure.
Measure charge inlet vacuum. Inspect line for proper sizing.
Replace filter. Confirm proper bypass operation.
Bypass valve
Slightly activated bypass valve will cause cross port leakage.
Verify that the bypass valve is closed and that the valve is
seating properly. Clean, repair, or replace it as necessary.
Service Manual
DDC20/24 Axial Piston Pumps
Troubleshooting
©
Danfoss | August 2019
L1120413 | AX00000135en-000401 | 13
