TM 1-1520-238-10
2-54
Change 4
(6) Rotor Brake Solenoid Valves.
Valves are
controlled by a three-position switch OFF, BRAKE, and
LOCK on the pilot PWR lever quadrant adjacent to the
PWR levers (fig 2-19). When the switch is positioned to
BRAKE, utility system pressure regulated to 337 psi is ap-
plied to stop the rotor brake disc on the main transmission.
When positioned to LOCK, the brake off solenoid valve
traps 3000 psi pressure between the manifold and the ro-
tor brake actuator.
b. Utility Accumulator.
The accumulator is a multi-
purpose installation unique to the utility hydraulic system.
It is located on the right side of the helicopter directly be-
neath the APU. It stores hydraulic fluid at 3000 psi. The
accumulator is charged by nitrogen gas. A gas storage
tank supplies the charge and is serviced through a charg-
ing port (fig 2-31). The utility hydraulic manifold pressure
is used for rotor brake application, APU starting, and
emergency use of flight control operation.
2.38.3 Hand Pump.
A hand pump is installed next to
the primary system GSE panel on the right side of the heli-
copter. The pump provides one method of charging the
fluid pressure in the utility accumulator as well as a meth-
od for the ground crew to fill both the primary and utility
reservoirs. Low pressure fluid entering the fill port is fil-
tered by a 45 micron screen filter (before MWO
1-1520-238-50-52) or a 5 micron cartridge filter (after
MWO 1-1520-238-50-52). A lever may be moved to any of
three positions. This, in turn, will open one of three me-
chanically operated check valves to the accumulator or to
either reservoir. Section XV contains servicing instruc-
tions.
2.39 PRESSURIZED AIR SYSTEM (PAS).
The PAS cleans, pressurizes, regulates, and distributes
air to the air turbine starters, fuel boost pump, fuel trans-
fer pump, external fuel tanks, hydraulic reservoirs, heat
exchangers, defog nozzles, engine cooling louver actua-
tors, utility receptacle, ice detector sensor, and environ-
mental control unit (ENCU). The pressurized air system
has three sources of air: The primary source is the shaft
driven compressor; the other sources are bleed air from
the No. 1 engine and from an external air source.
M01-137
UTILITY
MANIFOLD
CHARGING
PORT
Figure 2-31.
Utility Manifold
