TM 55-1520-240-23-6
7-135
UTILITY HYDRAULIC SYSTEM
(Continued)
7-135
Cargo Ramp and Door System Description
The ramp is hinged to the fuselage at the floor line and
supported by two actuating cylinders. The cylinders
are operated by hydraulic fluid through a control valve
to raise the ramp. The ramp lowers by gravity, with the
actuating cylinders serving as hydraulic dampers.
NO BREAK - WORK HARDER
The ramp can be stopped at any intermediate point on
its way up or down and hydraulically locked in position.
NO BREAK - WORK HARDER
A cargo door is an integral part of the ramp assembly.
When the ramp is up, the door is fully extended to
completely enclose the ramp area of the fuselage.
NO BREAK - WORK HARDER
When it is down, the door retracts into the ramp.
Extension and retraction is by a motor inside the ramp
that drives a sprocket and chain assembly. The motor
is controlled through a sequence valve that times the
doors motion to the position of the ramp. An override
valve allows the cargo door to remain open or closed
regardless of ramp position.
NO BREAK - WORK HARDER
The ramp system can be isolated from the rest of the
utility hydraulic system by a solenoid valve in the utility
pressure control module. The normally-open valve is
closed through a switch on the overhead HYDRAULIC
control panel in the cockpit.
NO BREAK - WORK HARDER
If normal pressure is not available from the utility
hydraulic system, the ramp can be operated by
pressurizing the system accumulator with the
handpump.
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