JLG 680S, Service And Maintenance Manual

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SECTION 5 - BASIC HYDRAULICS INFORMATION & SCHEMATICS
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5.3 PRESSURE SETTING PROCEDURE
Cold temperatures have a significant impact on pressure read-
ings. JLG Industries Inc. recommends operating the machine
until the hydraulic system has warmed to normal operating
temperatures prior to checking pressures. JLG Industries Inc.
also recommends the use of a calibrated gauge. Pressure read-
ings are acceptable if they are within ± 5% of specified pres-
sures.
To ensure all pressures are set correctly, the following proce-
dures must be followed in order.
1. All applicable steps in Section 5.4, Start Up Procedures
must be followed.
2. Set up of the function pump.
3. Adjustments made at the main valve block.
4. Adjustments made at the platform valve.
Set Up of the Function Pump
STAND BY PRESSURE OR LOAD SENSE PRESSURE
1. Install a low pressure gauge at port “M1” of the main
valve block. A low pressure gauge capable of reading
500 psi (34.5 bar).
2. Start the engine from the ground control. The gauge
should read between 400-440 psi (27.5 to 30 Bar). To
make an adjustment to this pressure, go to the engine
compartment and locate the function pump.
3. There are (2) adjustments at the top of the pump. They
are located on the pump compensator which has (4)
bolts mounting it to the pump. The stand by adjustment
is at the top. To adjust this, a 4 mm and 6 mm allen
wrench will be needed. The adjustment screw is facing
the front of the pump, or toward the engine.
a. First, using the 4 mm wrench, loosen the setscrew
on the side of the compensator (facing you) which is
in line with the adjustment screw. This is a jam nut
screw which holds the main adjustment from turn-
ing. Loosen it 1 turn.
b. Next, using the 6 mm wrench adjust the main
adjustment clockwise to increase or counterclock-
wise to decrease. The pressure should read between
400-440 psi (27.5 to 30 Bar).