National Crane Published 08/16/19 Control # 112-05 2-1
500E2 SERVICE MANUAL HYDRAULIC SYSTEM
SECTION 2
HYDRAULIC SYSTEM
SECTION CONTENTS
Hydraulic System Description. . . . . . . . . . . . . . . . 2-1
General Adjustment And Repair Procedures. . . . 2-1
Hydraulic System Maintenance Precautions . . . . 2-2
Label Parts When Disassembling . . . . . . . . . . . . . 2-2
Welding Precautions . . . . . . . . . . . . . . . . . . . . . . . 2-2
Hydraulic Oil Recommendations. . . . . . . . . . . . . . 2-2
Draining and Flushing. . . . . . . . . . . . . . . . . . . . . . 2-2
Removing Air From the Hydraulic System . . . . . . 2-3
Parts Replacement . . . . . . . . . . . . . . . . . . . . . . . . 2-4
Maintenance Records . . . . . . . . . . . . . . . . . . . . . . 2-4
Hydraulic Oil Reservoir . . . . . . . . . . . . . . . . . . . . . 2-4
Hydraulic Filter. . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4
Oil Cooler Service & Maintenance (Optional) . . . . 2-4
Servicing The Control Valves. . . . . . . . . . . . . . . . . 2-5
Disassembly And Reassembly Of Control
Valves To Replace Seals. . . . . . . . . . . . . . . . . . . . 2-5
Replacing Spool Seals. . . . . . . . . . . . . . . . . . . . . . 2-5
Unloader Valve Service . . . . . . . . . . . . . . . . . . . . . 2-6
Control Valve Relief Adjustment . . . . . . . . . . . . . . 2-7
HYDRAULIC SYSTEM DESCRIPTION
The hydraulic system of this machine is an open center type
consisting of a fixed displacement three section high
pressure pump which supplies oil to a main control valve and
a winch control valve. The main control valve is equipped
with a main inlet and a mid inlet. The main inlet supplies oil to
the turn function, the mid inlet supplies the remainder of the
crane function requirements. The main control valves
contain inlet section reliefs or port reliefs which limit pressure
in the hydraulic system to acceptable levels and control
crane movements. See Specification Section for pressure
settings.
The large single section control valve supplies oil to winch up
and down. The inlet section contains a screw adjustable
main relief. The first work section of the multi-section main
control valve controls turn right and left.This work section is
supplied oil by the main inlet section which contains a screw
adjustable relief valve. The remaining work sections are
boom telescope, boom lift, and outrigger functions in that
order. The oil to these sections is supplied by the mid inlet
section which also contains a main relief valve. The winch
and the main circuits are all connected through shuttles to a
pressure gage located on the control console.
The hydraulic oil is supplied by a truck frame mounted oil
reservoir, which is equipped with a replaceable canister type
return oil filter. The truck power take off driven hydraulic
pump is sized to supply 34 GPM (129 Lpm) to the winch
circuit, 18 GPM (68 Lpm) to the boom lift and telescope
circuits and 10 GPM (38 Lpm) to the turn function at 2500
rpm pump shaft speed. Higher pump speeds may result in
excessive heat generation in the hydraulic system. The
pump is not bidirectional and can only be used when the
shaft rotates only in the proper direction. If you need to verify
or change pump rotation, contact your National Crane
distributor or National Crane Product Support.
The crane hydraulic system includes a hydraulic capacity
alert system. This system is a hydraulically operated,
maximum capacity sensing device that monitors lift cylinder
pressure. As pressure in the lift cylinder approaches its
maximum predetermined level, which can be monitored on
the console mounted range gages, a hydraulic pressure
switch activates an integral hydraulic dump circuit in the
main control valve, disabling the crane functions which
increase the over capacity condition.
All load bearing cylinders on this machine are protected from
inadvertent movement or collapse due to hose failure by pilot
operated check valves or by pilot operated counterbalance
valves if overhung loads must be controlled.
The standard swing gearbox is locked in place by an integrally
mounted spring applied brake and a dual counterbalance motor
holding valve. The swing brake and counterbalances are piloted
open and closed by operating swing left or right and are
automatically reapplied by ceasing the swing function.
Maximum swing speed can be limited using the swing speed
adjustment valve.
GENERAL ADJUSTMENT AND REPAIR
PROCEDURES
Before adjustments and repairs are started on a crane, the
following precautions shall be taken as applicable:
• Place a warning tag in a conspicuous place at the
controls stating that the machine requires adjustment or
repair before it can be operated.
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