TM 55-1520-240-23-6
7-135
UTILITY HYDRAULIC SYSTEM
7-135
DESCRIPTION
The utility hydraulic system provides hydraulic pressure
to operate seven subsystems throughout the helicopter.
The systems are engine start, cargo ramp and door,
cargo winch, cargo hook release, power steering and aft
swivel locks, and wheel brakes. In addition, the system
can be used to pressurize the flight control system
during ground checks.
NO BREAK - WORK HARDER
The following components are common to all
subsystems:
APU Start Accumulators
This accumulator is used to store hydraulic fluid under
pressure to start the APU. It is located in the ramp area
to the right of the aft transmission. In an emergency,
the pressure in the accumulator can be used to operate
the utility subsystems.
APU Start Module
Pressure from the APU start accumulator is released
through the APU start module to the APU motorpump
when an APU start is called for. The module also signals
the APU motorpump to shift from motor mode to pump
mode as its rpm increases. The module contains a
depressurization valve that is used to repressurize the
start accumulator for maintenance.
NO BREAK - WORK HARDER
The start module is located in the ramp area, aft of the
APU start accumulator.
APU Motorpump
The motorpump is mechanically coupled to the forward
end of the APU. When serving as a motor, it receives
hydraulic pressure from the APU start accumulator to
drive the APU to starting speed. When the APU starts,
it drives the motorpump as a pump. As a pump, it
supplies pressurized hydraulic fluid at 3350 psi to start
the engines or to power the utility subsystems.
NO BREAK - WORK HARDER
The motorpump can also be used to power the utility
hydraulic system if the utility pump fails.
Utility Pump
When the engines are running and the rotor system is
turning, the entire utility system is pressurized by the
utility pump through the pressure control module. The
pump is installed on the right side of the aft transmission
and is driven by the transmission. It delivers hydraulic
fluid to the pressure control module at 3,000 to 3,100
psi.
Pressure Control Module
The pressure control module receives input hydraulic
pressure from the APU motorpump, the utility pump, or
an external ground power unit and distributes it to the
various utility subsystems. The module is located high
in the aft cabin area at sta. 534, to the right of the aft
sync shafting.
Return Control Module
This module is the central collection point for all
fluid returning from the various subsystems to the
reservoir/cooler. A filter and a transfer cylinder are
mounted on the module. The filter has a visual
contamination indicator and a switch to light a caution
light on the maintenance panel in the ramp area. The
transfer cylinder supplies fluid to the ramp system to
compensate for the additional flow required when the
ramp is lowered.
NO BREAK - WORK HARDER
The return module is located high in the aft cabin area
at sta. 534, to the left of the aft sync shafting.
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