JLG 740A, Service And Maintenance Manual

Page: 310 / 408

SECTION 5 - HYDRAULICS
5-24 – JLG Lift – 3121160
Table 5-7. Actuator Response Is Sluggish
Item Description Action
Check external system relief valve setting. Low external relief valve setting will slow down
system. Adjust external relief valve setting per manufac-
turer’s recommendations. External relief setting
must be above Pressure Compensator setting for
proper operation.
Check Pressure Compensator and LS control
setting. 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 Load Sense control signal pressures. Incorrect Load Sense signal will not allow pump to
operate correctly. Inspect system, ensure that proper Load Sense
signal is transmitted to the pump.
Internal system leaks. Worn internal parts will not allow the pump to
operate properly. Refer to Authorized Service Center for repairs as
required.
Hydraulic fluid viscosity above acceptable limits. Hydraulic fluid viscosity above acceptable limits
or low fluid temperature 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 valving. Malfunctioning valving may not allow system to
respond properly. Repair or replace system valving as required.
Check pump case pressure. High case pressure will cause the system to be
sluggish. Correct case drain line restrictions.
Check pump inlet pressure / vacuum. High inlet vacuum will cause low output flow. Correct inlet pressure conditions.
Table 5-8. System Operating Hot
Item Description Action
Check fluid level in reservoir. Insufficient volume of hydraulic fluid will not meet
cooling demands of system. Fill reservoir to proper level. Verify proper size of
reservoir.
Inspect heat exchanger. Check air flow and input
air temperature for the heat exchanger. Insufficient air flow, high input air temperature, or
undersized heat exchanger will not meet cooling
demands of the system. Clean, repair, or replace heat exchanger as
required. Verify proper size of heat exchanger.
Check external system relief valve setting. Fluid passing through relief valve adds heat to
system. Adjust external system relief valve setting per
manufacturer’s recommendations. External relief
valve setting must be above Pressure Compen-
sator setting for proper operation.
Check pump inlet pressure / vacuum. High inlet vacuum adds heat to system. Correct inlet pressure / vacuum conditions.