Pressure Setting Procedures; Main Relief; Main Lift Down Relief; Lower Lift Down Relief - JLG E450A Service And Maintenance Manual

SECTION 5 - BASIC HYDRAULIC INFORMATION & SCHEMATICS
5.5 MID AND LOWER LIFT CYLINDER BLEEDING
PROCEDURE
NOTE: Bleeding procedure should only be necessary if
rebuilding or replacing lift cylinder.
1. Check oil level in the hydraulic oil tank (all booms must
be retracted).
2. Lay an oil drip pan under the rod end port block (Mid
Cylinder) and crack bleeder open from the fitting in the
port block.
3. From the platform, turn the speed control knob to the
slow position.
4. Lift up very slowly. This will force any air out of the cir-
cuit. If the lower boom is not extending, turn the speed
control up very slowly until the lower boom starts to
move.
5. Raise the lower boom approximately. 30.5 cm (1 foot),
then close bleeder while the boom is still moving.
6. Lift down all the way.
7. Repeat this procedure until all air has been purged from
the circuit. Re-check the hydraulic oil level.
8. To test, cycle the lower lift function 3-4 times to see if
both cylinders stop at the same time when fully
extended.
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5.6 PRESSURE SETTING PROCEDURES

NOTE: Cold temperatures have a significant impact on pressure
readings. JLG Industries Inc. recommends operating the
machine until hydraulic system has warmed to normal
operating temperatures prior to checking pressures. We
also recommend using a calibrated gauge. Pressure read-
ings are acceptable if within +/- 5% of specified pressures.

Main Relief

1. Install pressure gauge at port "G" on Steer Valve.
2. Activate and bottom out either Main or Lower Lift Up.
Adjust Main Relief to value given in Figure 5-148., Steer
Valve Pressure Adjustment.

Main Lift Down Relief

1. With pressure gauge at "G" port on main valve, activate
and bottom out Main Lift Down.
2. Adjust Main Lift Relief to value given in Figure 5-151.,
Main Valve Pressure Adjustment.

Lower Lift Down Relief

1. With pressure gauge at "G" port on main valve, activate
and bottom out Mid/Lower Lift Down.
2. Adjust Mid/Lower Lift Relief to value given in Figure 5-
151., Main Valve Pressure Adjustment.

Telescope Relief

1. With pressure gauge at "G" port on main valve, activate
and bottom out Telescope In.
2. Adjust Telescope Relief to value given in Figure 5-151.,
Main Valve Pressure Adjustment.
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