Service Manual
Series 45 J Frame Open Circuit Axial Piston Pumps
520L0607
• Rev AI • Sep 2013
20
System Pressure not
Reaching PC Setting
High Inlet Vacuum
Caution
High inlet vacuum causes
cavitation which can damage
internal pump components.
Troubleshooting
(continued)
Pressure or Flow Instability
(continued)
Item
Description
Action
Check LS setting.
Low LS setting may cause
instability.
Adjust LS setting to proper level.
See
Adjustments
, page 21.
Check LS signal line.
Blocked LS signal line interferes
with proper LS operation.
Remove blockage.
Check external relief valve and PC
setting.
Insufficient pressure differential
between PC setting and external
relief valve.
Adjust external relief valve or PC
control settings to appropriate
level. Relief valve setting must be
above PC setting to operate
properly.
Check external relief valve.
Chattering external relief valve may
cause unstable feedback to pump
control.
Adjust or replace relief valve.
Item
Description
Action
Check PC control setting.
System pressure will not rise above
PC setting.
Adjust PC to appropriate setting.
Refer to
Adjustments
, page 21.
Check external relief valve.
External relief valve setting below
PC setting presents pressure
compensation.
Adjust external relief valve
according to manufacturer’s
recommendations. External relief
valve must be set above PC setting
to operate properly.
Inspect PC control spring.
Broken, damaged, or missing spring
will cause erratic operation.
Replace the spring as required.
Inspect PC spool for wear.
Wear of PC spool causes internal
leakage in the control.
Replace the spool as required.
Inspect PC spool for proper
orientation.
Improper orientation results in poor
operation.
Correct orientation of spool.
Check PC control for contamination. Contamination may interfere with
movement of the PC spool.
Clean PC control components, take
appropriate action to eliminate
contamination.
Item
Description
Action
Check fluid temperature.
Low temperature increases
viscosity. High fluid viscosity causes
high inlet vacuum.
Allow system to warm up before
operating.
Inspect inlet screen.
Blocked or restricted inlet screen
causes high inlet vacuum.
Clean screen/remove blockage.
Check inlet piping.
Too many fittings, bends, or long
piping causes high inlet vacuum.
Eliminate fittings to make path
more direct.
Hydraulic fluid viscosity above
acceptable limits.
High fluid viscosity causes high inlet
vacuum.
Select fluid with appropriate
viscosity for expected operating
temperature. See
Hydraulic Fluids
and Lubricants Technical Information
Manual,
520L0463
.
