Sluggish System Response - Danfoss DDC20 Service Manual

Service Manual
DDC20/24 Axial Piston Pumps
Troubleshooting
Cause Problem
Low charge Low charge pressure insufficient to recharge system loop
pressure with pump
in neutral
Low charge Low charge pressure resulting from elevated loop leakage.
pressure with pump
in stroke
Pump charge relief A pump charge relief valve that is leaky, or contaminated, or set
valve. too low will depressurize the system.
Charge pump inlet A clogged filter will under supply system loop.
filter.
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 Defective high pressure relief valves cause system pressure to
valves be low
Control Linkage Linkage operating improperly
DDC20/24 sluggish system response
Cause Problem
Oil level in reservoir Low oil level causes slower system response
High pressure relief Incorrect system pressures will affect system reaction time. High
valves pressure relief valve with orifice may affect system reaction
time.
Low prime mover Low engine speed will reduce system performance
speed
Air in system Air in system will produce slower 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.
© Danfoss | August 2019
Solution
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
Solution
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.
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