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(2) High-Pressure and Low-pressure Relief
Valves. Regulates fluid pressure from the pump and
the return to the manifold.
(3) Reservoir Low-Level Indication Switch.
Switch is activated by the manifold reservoir piston.
This illuminates an OIL LOW PRI HYD segment light
on the pilot caution/warning panel to indicate minimum
operating level.
(4) Fluid Level indicator. Located in the manifold
reservoir housing allows visual inspection of the
reservoir oil level.
(5) Filters. Filters on both manifold pressure
and return sides have mechanical impending bypass
indicators for visual inspection. These indicators operate
on differential pressure. Both impending bypass indicators
illuminate the OIL BYP PRI HYD segment
on the pilot caution/warning panel. Only the return filter
has bypass provisions.
TM 1-1520-238-10
Figure 2-29. Primary Hydraulic System
Change 4 2-51
TM 1-1520-238-10
(6) Pressure Switch. Senses primary system
pressure and informs the pilot and CPG of a low oil
pressure condition by illuminating the PRI HYD PSI
segment on the pilot caution/warning panel and PRI
HYD segment on the CPG panel. This switch illuminates
the segments until the system pressure is above
2050 psi and will again illuminate the segments when
pressure falls below 1250 psi.
(7) Pressure Transducer. Measures hydraulic
pressure on the pressure side of the manifold and
transmits this value to the left side of the pilot dual hydraulic
gauge.
2.38.2 Utility Hydraulic System. The utility hydraulic
system (fig 2-30) provides hydraulic power to the
utility side of the lateral cyclic, longitudinal cyclic, collective,
and directional servo actuators. This system
also provides hydraulic power to the rotor brake, area
weapon, external stores, tail-wheel lock, ammo carrier
drive, and APU starter. The utility hydraulic pump (on
the accessory drive case of the main transmission right
side) is identical to that in the primary system. The hydraulic
heat exchanger may still be installed on some
helicopters. The heat exchanger is obsolete and is being
removed through attrition. The only significant difference
in the two systems is the manifold, with an
associated accumulator and gas reservoir. Additional
components in the system are the accumulator, rotor
brake, and the utility hydraulic return accumulator
that dampens hydraulic pressure surges caused by sudden
actuation of the gun turret.
a. Utility Manifold. The utility manifold (fig 2-31)
is installed on the aft main fuselage deck on the right
side. It stores, filters, supplies, and regulates the flow
of utility hydraulic fluid. Demands on the utility system
are much greater than those on the primary system,
and the utility manifold installation is therefore
larger, with a reservoir capacity of 1.3 gallons. Total
system capacity is about 2.6 gallons. An air-pressure
reliefvalve, low-pressure reliefvalve, high-pressure relief
valve, reservoir low-level indicating switch, fluidlevel
indicator, return filter, pressure filter, pressure
switch, and pressure transducer, are identical in function
to the primary system components. The pilot caution/
warning panel provisions are also similar; but the
lights are labeled OIL LOW UTIL HYD, OIL BYP
UTIL HYD, and UTIL HYD PSI. Low utility hydraulic
pressure also illuminates the CPG UTIL HYD light.
2-52
The utility manifold also incorporates several other features
not duplicated on the primary manifold. These
are the utility accumulator hydraulic pressure transducer
and rotor brake solenoids.
(1) Low-Level and Auxiliary isolation
Valves. Permit hydraulic fluid to flow to the external
stores, ammo carrier drive, tail wheel lock actuator,
and area weapon turret. If the reservoir fluid level decreases
significantly, the reservoir piston, driven by
PAS air, will contact and close the low-level valve. The
auxiliary isolation valve, which normally requires two
sources of pressure to permit fluid flow, will then close
and deny hydraulic power to the area weapon turret,
the external stores actuators, and the ammo carrier
drive.
(2) Shutoff Valve. Located in the pressure line
to the directional servo and TAIL WHL unlock actuator
is actuated by the low-level switch in the utility system
reservoir. The utility side of the directional servo actuator
and the TAIL WHL unlock actuator will be inoperative
if a low utility system fluid level is sensed.
(3) Accumulator isolation Valve. Normally
isolates accumulator pressure from the rest of the utility
system but allows system flow from the pump to
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