JLG 1850SJ, Service And Maintenance Manual, Page: 386 / 712

SECTION 5 - BASIC HYDRAULIC INFORMATION & HYDRAULIC SCHEMATICS
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Table 5-37. System will not operate
Item Description Action
Oil level in reservoir Insufficient hydraulic fluid to supply system loop. Fill reservoir to proper level.
Control orifices Control orifices are blocked. Clean control orifices.
Control screens Control screens are blocked. Clean or replace control screens.
Charge pressure with pump in neutral Low charge pressure insufficient to recharge sys-
tem loop. Measure charge pressure with the pump in neu-
tral. If pressure is low, go to next step.
Pump charge relief valve A pump charge relief valve that is leaky, contami-
nated, or set too low will depressurize the sys-
tem. Adjust or replace pump charge relief valve as nec-
essary.
Charge pump inlet filter A clogged filter will under supply system loop. Inspect filter and replace if necessary.
Charge pump A malfunctioning charge pump will provide
insufficient charge flow. Repair or replace the charge pump.
System pressure Low system pressure does not provide enough
power to move load. Measure system pressure. Continue to next step.
Charge check / HPRVs Defective charge check / HPRVs cause system
pressure to be low. Repair or replace charge check / HPRVs.
Input to control Input to control module is operating improperly. Repair or replace control.
Optional control cutoff valve Control cutoff valve coil not energized. Ensure charge pressure to control via port X7. If
none, confirm control cutoff valve coil is ener-
gized. If still no pressure, repair or replace control
cutoff valve.
Table 5-38. System noise or vibration
Item Description Action
Reservoir oil level Low oil level leads to cavitation. Fill reservoir.
Aeration of the oil/pump inlet vacuum Air in system decreases efficiency of units and con-
trols. Air in system is indicated by excessive noise in
pump, foaming in oil, and hot oil. Find location where air is entering into the system
and repair. Check that inlet line is not restricted and
is proper size.
Cold oil If oil is cold, it may be too viscous for proper function
and pump cavitates. Allow the oil to warm up to its normal operating
temperature with engine at idle speed.
Pump inlet vacuum High inlet vacuum causes noise/cavitation. Check that inlet line is not restricted and is proper
size. Check filter and bypass switch.
Shaft couplings A loose input shaft to prime mover coupling will
cause excessive noise. Replace loose shaft coupling.
Shaft alignment Misaligned input and prime mover shafts create
noise. Correct misalignment.
Charge/system relief valves Unusual noise may indicate sticking valves. Possible
contamination. Clean/replace valves and test pump. May be a nor-
mal condition.