JLG 1850SJ Service Manual - Manual (Page 262)

SECTION 5 - BASIC HYDRAULIC INFORMATION & HYDRAULIC SCHEMATICS
5-92 – JLG Lift – 3121619
SYSTEM OPERATING HOT
LOW PUMP OUTPUT
UNSTABLE PRESSURE OR FLOW
Item Description Action
Check fluid level in reservoir. Insufficient volume of hydraulic fluid will not meet sys-
tem cooling demands
.
Fill reservoir to proper level. Verify proper size of reser-
voir.
Inspect heat exchanger. Check air flow and input air tem-
perature for heat exchanger. Insufficient air flow, high input air temperature, or
undersized heat exchanges will not meet system cooling
demands. Clean, repair, or replace heat exchanger as required. Ver-
ify 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 following
manufacturer’s recommendations. External relief
valve setting must be above PC setting for proper opera-
tion.
Check pump inlet pressure/vacuum. High inlet vacuum adds heat to system. Correct inlet pressure/vacuum
conditions.
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 tem-
perature will not allow the pump to fill or control to oper-
ate properly. Allow system to warm up before operating, or use fluid
with the appropriate viscosity grade for expected operat-
ing temperatures.
Check external system relief valve
setting Eternal relief valve set below PC setting causes low out-
put flow. Adjust external relief valve following manufacturer’s
recommendation. External relief valve setting must be
above PC setting to operate properly.
Check PC and LS control setting. Low PC setting prevents the pump from achieving full
stroke. Adjust PC and LS setting.
Check pump inlet pressure/vacuum. High inlet vacuum causes low output flow. Correct inlet pressure conditions.
Check input speed. Low input speeds decrease flow. Adjust input speed.
Check pump rotation. Incorrect rotational configuration causes low flow. Use pump with appropriate rotational configuration.
Item Description Action
Check for air in system. Air in system causes erratic operation. Activate PC allowing system to bleed air. Check inlet line
for leaks and eliminate source of air ingression.
Check control spools. Sticking control spools cause erratic operation. Inspect spools for free movement. Clean or replace.
Check LS setting. Low LS setting may cause instability. Adjust LS setting to proper level.
Check LS signal line. Blocked LS signal line interferes with proper LS opera-
tion. 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 feed-
back to pump control. Adjust or replace relief valve.