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CHAPTER 1 GENERAL INFORMATION AND OPERATING INSTRUCTIONS
NMC-WOLLARD
2021 Truax Blvd. Eau Claire, WI 54703 ● P: 715-835-3151● F: 715-835-6625 ● www.nmc-wollard.com
TML-704H Maintenance Lift Manual No. 310547
1 DESCRIPTION
1.4.5 Independent Hydraulic System
The independent hydraulic system powers the platform raise/lower, stabilizer
raise/lower, and power steering functions of the unit. The system consists of
the engine-driven hydraulic pump, electric-driven hydraulic pump, oil
reservoir, control valves, oil lters, and hydraulic work cylinders (stabilizer,
steering and platform lift); check, ow control and gate valves; and the
associated plumbing, ttings and hoses.
Hydraulic Oil Reservoir
See Chapter 2 for uid specication and capacity.
The hydraulic oil reservoir is behind the operator's station. The tank is made
of welded aluminum to reduce internal corrosion and scale buildup. The
reservoir is tted with a magnetic drain plug, sight gauge, and a vented ller/
strainer installed in the center of a cleanout cover.
A shuto valve and an 80-mesh external Y-strainer are installed in the suction
line between the reservoir and the pumps. A 10-micron lter unit, with a
replaceable element and a shuto valve are installed in the return line.
Hydraulic Pumps
Two hydraulic pumps are in the independent hydraulic system. The main
pump is driven by the vehicle engine. The other pump is electric-driven and is
powered by the alternator/battery electric system. The electric pump functions
on demand as an emergency unit only. Check valves on the pressure lines for
both pumps prevent interaction between pumps. The engine-driven pump is a
xed-displacement gear type mounted on the engine package. The main
pressure relief valve is with the engine package and limits system pressure to
a specied setting. All main valves in the system are open-center types and
allow unused hydraulic oil to return freely to reservoir when no functions are
being used.
Platform Lift System
The platform assembly is raised and lowered by a single-acting work cylinder
installed within the scissor assembly. A pilot-operated check valve installed on
the cylinder locks the cylinder in place when in raised (extended) position.
The platform is not powered down-the cylinder retracts because of the weight
of the platform and scissor assemblies. Check valves allow oil to be diverted
from cylinder blind end directly to rod end to keep rod end full of oil when
lowering the platform.
How the Platform Works
Actuating and/or holding the "Operational (Platform) Safety" switch energizes
Operate Safety Valve SV3, diverting oil from the Power Steering Unit to
directional valve bank SV1/SV2. This is necessary to provide hydraulic power
for the lift and stabilizer functions.
SEPTEMBER 01, 2015
Property of American Airlines
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