System Will Not Operate In Either Direction; Sluggish System Response - Danfoss DDC20 Service Manual

Service Manual
DDC20 Axial Piston Pumps
Troubleshooting

System will not operate in either direction

Item Description
Oil level in reservoir Low oil level leads to cavitation.
Open bypass valve If bypass valve is open, the system loop will be
depressurized.
Low charge pressure with Low charge pressure insufficient to recharge system loop
pump in neutral
Low charge pressure with Low charge pressure resulting from elevated loop leakage.
pump in stroke
Pump charge relief valve. A pump charge relief valve that is leaky, or contaminated,
or set too low will depressurize the system.
Charge pump inlet filter. A clogged filter will under supply system loop.
Charge pump. A malfunctioning charge pump will provide insufficient
charge flow.
System pressure Low system pressure does not provide enough power to
move load
High pressure relief valves Defective high pressure relief valves cause system pressure
to be low
Control Linkage Linkage operating improperly

Sluggish system response

Item Description
Oil level in reservoir Low oil level causes sluggish response
High pressure relief valves Incorrect system pressures will affect system reaction time.
High pressure relief valve with orifice may affect system
reaction time.
Low prime mover speed Low engine speed will reduce system performance
Air in system Air in system will produce sluggish system response
Pump inlet vacuum Inlet vacuum is too high resulting in reduced system
pressure.
Bypass valve Slightly activated bypass valve will cause cross port
leakage.
14 | © Danfoss | August 2017
Action
Fill reservoir.
Close bypass valve.
Measure charge pressure with the pump in neutral. If
pressure is low, go to Pump charge relief valve
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).
Replace pump charge relief valve as necessary
Inspect filter and replace if necessary.
Repair or replace the charge pump.
Measure system pressure. Continue to next step.
Replace high pressure relief valves.
Repair/replace control linkage
Action
Fill reservoir
Replace high pressure relief valves
Adjust engine speed
Fill tank to proper level. Cycle system slowly for several
minutes to remove air from system
Measure charge inlet vacuum. Inspect line for proper sizing.
Replace filter. Confirm proper bypass operation.
Verify that the bypass valve is closed and that the valve is
seating properly. Clean, repair, or replace it as necessary.
L1120413 | AX00000135en-US0302