JLG 723A Service Manual - Manual (Page 87)

8-5 L2906H, 2906H, 3507H, 619A, 723A, 29.6LP, 29.6, 35.7
Hydraulic System
NEVER replace a hydraulic hose or other component
with a part not specifically designed for this machine. Use
only factory approved parts for best performance and
safety.
Removal and replacement of hoses, tube lines, fittings,
etc. usually involves straightforward procedures. When
removing a hydraulic hose or other component, be aware
that o-rings are used throughout the hydraulic system.
ALWAYS replace a used o-ring with a new part.
Check all routing of hoses, wiring and tubing for sharp
bends or interference with any rotating members. Install
appropriate protective devices such as tie wraps and
conduit to help shield hoses from damage. All tube and
hose clamps must be tight.
8.6 HYDRAULIC PRESSURE DIAGNOSIS
8.6.1 Pressure Checks and Adjustments
In general, follow the steps below whenever conducting
pressure checks and performing adjustments:
1. Park the machine on a firm, level surface. Engage
the park brake, place the transmission control lever
in (N) NEUTRAL, place the neutral lock lever in the (N)
NEUTRAL LOCK position, level the boom and turn
the engine OFF.
2. Pressure tee fittings are conveniently located in
each hydraulic circuit. Install a pressure gauge
capable of measuring at least 10% more pressure
than that which the circuit being checked operates
under.
3. Start the engine. Operate machine functions several
times to allow hydraulic oil to reach operating
temperature. The hydraulic oil temperature should
be between 38-49° C (100-120° F). If a temperature
gauge or thermometer is unavailable, the hydraulic
oil reservoir should be warm to the touch.
4. Fully depress the accelerator pedal as required.
Place and hold the joystick in the position needed to
operate the particular machine function being
checked. Continue holding the joystick in position
until pressure readings are taken.
5. Check the pressure gauge reading. It should read as
described in the appropriate section. If the reading is
not as specified, turn the engine OFF and check
other components in the system. Verify that all
related hydraulic components and electrical
switches, sensors, solenoids, etc. are operating
correctly.
6. As a last resort, adjust the appropriate relief valve, if
applicable. Turning the adjustment screw clockwise
will increase the pressure; turning the screw
counterclockwise will decrease the pressure.
8.6.2 Main Control Valve Pressure Checking
Attach 345 bar (5000 psi) gauge to the test port (1) at the
rear of the implement pump to check the system
pressure. Make sure the gauge is visible from inside the
cab.
See Section 8.6, “Hydraulic Pressure Diagnosis,” for start
up procedure. Check the main control pressure with the
park brake on and the service brake off at full throttle.
Retract a boom circuit function until the cylinder bottoms.
The main control valve pressure should be 250 ± 2,8 bar
(3625 ± 40 psi) at full throttle. Repeat for each boom
circuit to verify the correct main control valve pressure.
If a pressure adjustment is required, adjust the main relief
cartridge (2) on the main control valve. Recheck pressure
after any adjustment has been made.
MZ5500
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