JLG 740AJ, Service And Maintenance Manual

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SECTION 5 - BASIC HYDRAULIC INFOR M ATION AND SCHE M ATICS
3121160 5-85
Table 5-5. Low Pump Output Flow
Item Description Action
Check fluid level in reservoir. Insufficient hydraulic fluid will limit output flow and cause
internal damage to pump.
Fill the reservoir to proper level.
Hydraulic fluid viscosity above acceptable limits. Fluid viscosity above acceptable limits or low fluid temper-
ature will not allow the pump to fill or control to operate
properly.
Allow system to warm up before operation or use fluid with
the appropriate viscosity grade for expected operating
temperatures.
Check external system relief valve setting. External relief valve set below Pressure Compensator set-
ting will cause low output flow.
Adjust external relief valve per manufacturer’s recommen-
dation. External relief valve setting must be above Pressure
Compensator setting for proper operation.
Check Pressure Compensator and Load Sense control set-
ting.
Low Pressure Compensator setting will prevent the pump
from achieving full stroke. Low Load Sense setting will
limit output flow.
Adjust Pressure Compensator and Load Sense setting.
Refer to Adjustments.
Check pump inlet pressure / vacuum. High inlet vacuum will cause low output flow. Correct inlet pressure conditions.
Check input speed. Low input speeds decrease flow. Adjust input speed.
Check pump rotation. Incorrect rotational configuration will cause low flow. Use pump with appropriate rotational configuration.
Table 5-6. Pressure or Flow Instability
Item Description Action
Check for air in system. Air in system will cause erratic operation. Activate Pressure Compensator, allowing system to bleed
air. Check inlet line for leaks and eliminate source of air
ingression.
Check control spools. Sticking control spools will cause erratic operation. Inspect spools for free movement in bore. Clean or replace
as needed.
Check Load Sense setting. Low Load Sense setting may cause instability. Adjust Load Sense setting to proper level. See Adjust-
ments.
Check Load Sense signal line. Blocked Load Sense signal line will interfere with proper
Load Sense operation.
Remove blockage.
Check external relief valve and Pressure Compensator set-
ting.
Insufficient pressure differential between Pressure Com-
pensator Pressure Compensator setting and external relief
valve.
Adjust external relief valve or Pressure Compensator con-
trol settings to appropriate level. Relief valve setting must
be above Pressure Compensator setting for proper opera-
tion.
Check external relief valve. Chattering external relief valve may cause unstable feed-
back to pump control.
Adjust or replace relief valve.