Hydraulic Reservoir; Hydraulic System Pump; Pressurized Hydraulic Oil Fill Cap; Hydraulic Oil Reservoir Draining - JLG G5-18A Service Manual

8.7

HYDRAULIC RESERVOIR

The hydraulic reservoir and fuel tank are part of the
frame. For this reason, neither tank can be removed. For
cleaning instructions, see Section 7.6.2, "Fuel/Hydraulic
Oil Tank."
Occasionally, fluid may seep, leak or be more forcefully
expelled from the filter head when system pressure
exceeds the rating of the filter head or filler cap. If the
return filter becomes plugged, return hydraulic oil will
bypass the filter when pressure reaches 22 psi (1,5 bar)
and return to the reservoir unfiltered.
Carefully examine fluid seepage or leaks from the
hydraulic reservoir to determine the exact cause. Clean
the reservoir and note where any seepage occurs.
Leaks from a cracked or damaged reservoir require that
the reservoir be flushed completely with water and
repaired by a certified welder using approved techniques.
If these conditions cannot be met, the reservoir must be
replaced in its entirety. Contact your local JLG distributor
should reservoir welding be required.
8.7.1

Pressurized Hydraulic Oil Fill Cap

The fill cap will allow the hydraulic oil reservoir to
pressurize to 2 psi (0,14 bar). Inspect the condition of the
cap seal to maintain proper reservoir pressure.
8.7.2

Hydraulic Oil Reservoir Draining

1. Park the machine on a firm, level surface, fully
retract the boom, support the boom, place the
transmission control lever in (N) NEUTRAL, engage
the park brake and shut the engine OFF.
2. Place an Do Not Operate Tag on both the ignition
key switch and the steering wheel, stating that the
machine should not be operated.
3. Open the engine covers. Allow the system fluids to
cool.
4. Remove the drain plug at the bottom of the hydraulic
oil reservoir.
5. Transfer the used hydraulic oil into a suitable,
covered container, and label as "Used Oil". Dispose
of used oil at an approved recycling facility. Clean
and reinstall the drain plug.
6. Wipe up any spilled hydraulic oil.
G5-18A, 2505/2505
8.7.3

Hydraulic Oil Reservoir Filling

1. Be sure the reservoir is clean and free of all debris.
2. Install new hydraulic oil filters.
3. Fill the reservoir with Mobilfluid
oil. Refer to Section 2.3, "Fluids, Lubricants and
Capacities."
4. Start the machine. Run engine to normal operating
temperature. Operate all hydraulic functions.
8.8

HYDRAULIC SYSTEM PUMP

8.8.1

Implement Pump Failure Analysis

The implement pump is the "heart" of the hydraulic
system, and whenever there is a problem in the system,
the pump often is blamed. However, implement pump
failure is seldom due to failure of pump components.
Pump failure usually indicates another problem in the
hydraulic system.
According to pump manufacturer statistics, 90-95 percent
of pump failures are due to one or more of the following
causes:
• Aeration
• Cavitation
• Contamination
• Excessive Heat
• Over-Pressurization
• Improper Fluid
In the event of pump failure, investigate further to
determine the cause of the problem.
8.8.2

Implement Pump Replacement

a. Implement Pump Removal
1. Park the machine on a firm, level surface, fully retract
the boom, support the boom, place the transmission
control lever in (N) NEUTRAL, engage the park brake
and shut the engine OFF.
2. Place an Do Not Operate Tag on both the ignition
key switch and the steering wheel, stating that the
machine should not be operated.
3. Open the engine covers. Allow the system fluids to
cool.
4. Drain the hydraulic oil reservoir. Refer to Section
8.7.2, "Hydraulic Oil Reservoir Draining."
5. Thoroughly clean the pump (1) and surrounding
area, including all hoses and fittings before
proceeding.
Hydraulic System
®
424 (ISO Grade 46)
8-11