TM 1-1520-238-T-5
Change 6
7–27
7–7.
SYSTEM DESCRIPTION (cont)
7–7
c. Utility Hydraulic System.
(1) Purpose.
The purpose and use of the utility hydraulic system is to provide hydraulic pressure for
electrical or mechanical directional control of flight control servocylinders, APU start motor, rotor brake, tail wheel
lock actuator, pylon actuators, and weapon system components. The utility hydraulic system provides high
pressure for emergency operation of flight control servocylinders. A return accumulator provides area weapon
system (AWS) return pressure dampening. The utility hydraulic system provides visual indications of system
status.
(2) System Operation (fig. 7–12).
(a) The utility hydraulic pump draws low pressure fluid from the utility hydraulic manifold reservoir to
provide pressurized hydraulic fluid of 3000 psi to the utility hydraulic manifold. Fluid is then sent past a pressure
switch, filters, and a pressure transducer before exiting the utility hydraulic manifold. Output of the utility manifold
provides high pressure hydraulic fluid to the longitudinal, collective, lateral, and directional servocylinders, four
external stores controllers, AWS azimuth and elevation motors, and utility accumulator via a restrictor valve. The
utility hydraulic manifold supplies hydraulic pressure to the rotor brake using the pilot power quadrant RTR BK
switch and tail wheel control valve using the pilot TAIL WHEEL LOCK switch. During initiation of the APU start
sequence, the APU start motor is supplied with hydraulic pressure from the accumulator. Pressurized fluid in the
accumulator can also be used as a limited source for flight control servocylinders. An emergency hydraulic shutoff
valve shuts off the flow of fluid to the directional servocylinders and tail wheel lock control valve when the fluid
level is low. The hydraulic return accumulator dampens hydraulic pressure spikes generated by the AWS. The
fluid is then returned to the utility hydraulic manifold reservoir. The utility hydraulic manifold reservoir is serviced
and bled through the UTILITY GSE panel and the AGPU, or through use of a hand pump and a container of
hydraulic fluid. The low pressure fluid is filtered by a 45 micron screen filter (ADF) or a 5 micron cartridge filter
element (ADG). Nitrogen servicing of the accumulator is also accomplished at the UTILITY GSE panel.
