SkyTrak 6036 Service Manual - Manual (Page 277)

8.61 Model 6036 Legacy
Hydraulic System
Occasionally, fluid may seep, leak or be more forcefully
expelled from the filter head (Fig. 8 -26, 11) when system
pressure exceeds the rating of the filter head or breather.
If the return filter becomes plugged, return hydraulic oil
will bypass the filter when pressure reaches 25 psi
(1,7 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 removed from the vehicle, 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
JLG or the nearest JLG Authorized Service Center (ASC)
should reservoir welding or replacement be required.
8.10.1 Hydraulic Reservoir Replacement
The fuel tank and the hydraulic reservoir (Fig. 8-26, 1
and 2) are one unit and are removed together. Refer to
Section 7.8.2, “Fuel/Hydraulic Oil Tank” for information
on the fuel tank/hydraulic reservoir removal. Support the
fuel tank/hydraulic reservoir with a suitable device. Loos-
en, but DO NOT remove, the hex nuts (10) on the car-
riage assemblies. Slide the unit to the left to allow the
carriage bolt heads to come through the slots in the
frame.
Install the replacement fuel tank/hydraulic reservoir
(Fig. 8-26, 1 and 2) sliding the carriage bolt assemblies
into the slots in the frame. Slide the unit to the right and
secure it to the vehicle by tightening the hex nuts (10).
8.11 HYDRAULIC SYSTEM PUMP
The gear pump (Fig. 8-27) is attached to the transmission
and driven by the pump main shaft by meshing with an
internal transmission gear.
Figure 8-27 Gear Pump
The pump draws fluid through a 2" inside diameter hose
via negative displacement.
Fluid is forced from the pump through a 3/4" inside
diameter hose to the unloader valve. Hydraulic system
pressure begins at the pump. Various factors are involved
in creating the relatively high pressure used in the hydraulic
system. Pump rpm, controlled via a transmission input
shaft (and dependent on engine rpm), the internal pump
gears and passageways and the differential between
pump inlet (2" I.D.) and outlet (3/4" I.D.) openings, all
contribute to pressure supplied to the unloader valve. The
unloader valve ultimately regulates maximum system-
operating pressure of 3000 psi (207 bar) for various
vehicle functions.
8.11.1 Pump Failure Analysis
The pump is the “heart” of the hydraulic system, and
when there is a problem in the system, the pump often is
blamed. Yet, 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.
DANGER:
NEVER weld in, on, near or
around the hydraulic reservoir. Hydraulic fluid
and fumes can cause the reservoir to explode.
This can result in death or serious personal
injury.
MT1690