JLG G5-18A Service Manual - Manual (Page 96)

Hydraulic System
8-6 G5-18A, 2505H, 25.5
8.6.3 Charge Pressure Checking
1. Attach a pressure gauge to the test port (3) on the
hydrostatic transmission (4) to check the system
pressure. The pressure should be 350-410 psi
(24,1- 28,2 bar) with the engine at low idle.
2. The charge pressure relief valve is preset at the
factory and is not adjustable.
8.6.4 Boom Function Pressure Checking
1. Attach 5000 psi (345 bar) gauge to the test port (5)
at the rear of the implement pump to check the
system pressure. Make sure the gauge is visible
from inside the cab.
2. See Section 8.6, “Hydraulic Pressure Diagnosis,” for
start up procedure. Check the boom function
pressure with the park brake on and the service
brake off at full throttle. Retract each boom circuit
function until the cylinder bottoms. Each circuit
function pressure should be 3585-3665 psi
(247-252,7 bar) at full throttle.
Note: With the machine at operating temperature, the
3585-3665 psi (247-252,7 bar) pressure reading at the
main control valve is 125 psi (13,3 bar) HIGHER than the
3450-3550 psi (237,8-244,7 bar) of each individual valve
section function. DO NOT adjust the main control valve
relief pressure below 3585-3665 psi (247-252,7 bar).
To check individual valve section pressures, install a tee
and test port between the cylinder being checked and
the corresponding valve section on the main control
valve.
The individual valve section relief valves are preset at the
factory and are not adjustable.
8.6.5 Steering Pressure Checking
1. Attach a pressure gauge to the test fitting (5) at the
rear of the implement pump. The pressure reading
should be 2490-2590 psi (171,7-178,6 bar) with the
steering wheel fully turned to the steering stop in
one direction.
2. There is no adjustment for steering pressure.
8.6.6 Fan Speed Pressure and Direction
Checking
1. Place a piece of paper over the face of the radiator
core. If the paper is held in place, the fan is rotating
in the right direction.
2. Attach a pressure gauge to the test fitting (6) at the
rear of the implement pump.
3. If the machine is equipped with either the variable
fan option or the variable, reversing fan option; run
the engine at high idle and measure the fan speed
using a suitable portable stroboscope adjustable to
fractional RPM, and with the ability to distinguish
actual RPM from harmonic frequencies. The fan
speed must be a minimum of 2800 RPM at high idle.
4. Connect the JLG Analyzer and activate the Test
Mode to drive the fan to the maximum fan RPM.
Note: Refer to
5. The pressure reading should be 2400 psi (166 bar)
at high idle.
MY8650
4
3
MY8640
5
6