Troubleshooting; Overview; System Operating Hot; Transmission Operates Normally In One Direction Only - Danfoss DDC20 Service Manual

Service Manual
DDC20 Axial Piston Pumps

Troubleshooting

Overview

System operating hot

Item Description
Oil level in reservoir. Insufficient hydraulic fluid will not meet cooling demands
of system.
Heat exchanger. Heat exchanger not sufficiently cooling the system.
Charge pressure. Low charge pressure will overwork system.
Charge pump inlet vacuum. High inlet vacuum will overwork system. A dirty filter will
increase the inlet vacuum. Inadequate line size will restrict
flow.
System relief pressure If the system relief valves are worn, contaminated, or valve
settings. settings are too low, the relief valves will be overworked.
System pressure. Frequent or long term operation over system relief setting
will create heat in system

Transmission operates normally in one direction only

Item Description
Control linkage Control linkage operating improperly
High pressure relief valve Malfunctioning HPRV can affect one direction while the
other functions normally.

System noise or vibration

Item Description
Oil level in reservoir Low oil level leads to cavitation.
Aeration of the oil/pump Air in system decreases efficiency of units and controls. Air
inlet vacuum in system is indicated by excessive noise in pump, foaming
in oil, and hot oil.
Cold oil If oil is cold, it may be too viscous for proper function and
cause cavitation
Pump inlet vacuum High inlet vacuum causes noise/cavitation.
Shaft couplings A loose shaft coupling will cause excessive noise.
Shaft alignment Misaligned shafts creates noise
Charge/High pressure relief Unusual noise may indicate sticking valves. Possible
valves contamination.
© Danfoss | August 2017
This section provides general steps to follow if you observe undesirable system conditions. Follow these
steps until you solve the problem. Some of the items are system specific. For areas this manual covers, we
reference the section. Always observe the safety precautions listed in
precautions related to your specific equipment.
Introduction
Action
Fill reservoir to proper level.
Check air flow and input air temperature for heat
exchanger. Clean, repair or replace heat exchanger.
Measure charge pressure. Inspect and/or replace charge
relief valve. Inspect charge pump. Repair or replace charge
pump.
Check charge inlet vacuum. If high, inspect inlet filter and
replace as necessary. Check for adequate line size, length or
other restrictions
Verify settings of high pressure relief valves and replace
valves as necessary.
Measure system pressure. If pressure is too high, reduce
loads.
Action
Repair/replace control linkage
Exchange the high pressure relief valves. If the problem
changes direction, replace the valve that does not operate
correctly. Settings may be different for forward/reverse.
Action
Fill reservoir.
Find location where air is entering into the system and fix.
Check that inlet line is not restricted and is proper size.
Allow the oil to warm up to its normal operating
temperature with engine at idle speed.
Check that inlet line is not restricted and is proper size.
Check filter and bypass valves (if present).
Replace loose shaft coupling.
Align shafts.
Clean/replace valves and test pump. May be a normal
condition.
L1120413 | AX00000135en-US0302 | 13
on page 4, and