FAM 114

Utility Hydraulic System
2. The utility hydraulic power system supplies hydraulic fluid (MIL-H-83282) at a nominal pressure of 3,500 PSI at zero flow (without AFC 484) or 3,475 PSI (with AFC 484) and a minimum of 3,350 PSI at full flow to operate the main engine start system, Engine Air Particle Separator (EAPS) system, Engine Exhaust Device (EED) system (without AFC 475), cargo hoist subsystem, external rescue hoist subsystem, and the Power Transfer Unit (PTU). A reduced pressure of 3,000 PSI operates the ramp and hatch subsystem, rotor positioning subsystem, and fluid cooler. A reduced pressure of 1,215 PSI operates the rotor brake subsystem.

a. The utility system pump is mounted on and driven by the aft transmission. The pump is the primary source of pressurized fluid for the utility systems when the rotors are turning. Helicopters with AFC 484 have an improved utility hydraulic pump.

b. A hydraulic pump-motor on the Auxiliary Power Unit (APU) supplies fluid at 3,450 PSI at zero flow and a minimum of 3,300 PSI at full flow to start the main engines and operate the utility subsystems on the ground. The pump-motor operates as a hydraulic pump when the APU is running. It also operates as a motor to start the APU gas turbine engine and to supply fluid pressure to the PTU during ground operations. The APU pump-motor does not have sufficient flow to operate the EED at full speed.

c. Pressure reducing valves in the utility system and the rotor brake subsystem reduce 3,500 PSI (without AFC 484) or 3,475 PSI (with AFC 484) to a nominal 3,000 PSI in all the utility subsystems except the EED, EAPS, and the hoist systems.

3. Auxiliary Power Unit Start Modules. The APU start module contains an APU start valve, five cubic-inch accumulator, APU start sequence valve, four check valves, and bleed valve. The APU start module is mounted at FS 531 below WL 44, above the hatch hinge.

4. '''Engine Air Particle Separator Control Module.''' The EAPS control Module contains a solenoid fan control valve, two flow regulators, fan motor replacement indicators, and five check valves. There are two EAPS control modules, one each for the right and left engines. They are mounted on the right and left sides of the cabin ceiling, forward of FS 410.

5. Rescue Hoist and Boom Control Module. The rescue hoist boom and control module contains a hoist brake and power solenoid valve, boom control solenoid valve, flow regulator, hoist brake and power pilot valve, relief valves, and two check valves. The rescue hoist module is mounted on the cabin ceiling, aft of FS 168.

6. HANDPUMP. A hydraulic handpump on the right side of the aft fuselage (FS 425, WL 10) can be used for the following functions: a. To pressurize the accumulator for starting the APU.

b. To manually pressurize the utility hydraulic subsystems in a hydraulic power failure or during ground servicing. To replenish the pressurized reservoir by pumping fluid from a hydraulic filler into the return line. d. To bleed the utility hydraulic system.

7. FLUID COOLER. A fluid cooler is mounted in the aft pylon. It cools the fluid discharged by the rotor positioning motor, case drains from the utility system pump, APU pump-motor, rotor positioning motor, EAPS fan motors, EED fan motors (without AFC 475), external rescue hoist, and cargo winch. A hydraulic driven cooling fan draws air through the cooler. The cooler motor shuts down during engine starting.

8. PRESSURIZED RESERVOIR (TANK). An airless, pressurized reservoir is mounted in the aft pylon. It maintains the return fluid pressure at approximately 69 PSI when system pressure is 3,000 PSI.

9. POWER TRANSFER UNIT. The power transfer unit is mounted in the aft fuselage at FS 509, WL 33. The hydraulic motor portion of the unit is driven by hydraulic fluid supplied from the APU pump-motor. The hydraulic pump portion of the unit uses No. 2 flight control system fluid to operate the flight control system. The pump portion can be used to check out the flight control system during ground operations. A POWER TRANSFER UNIT switch, with ON and OFF positions, is provided to control the PTU should the No. 2 flight control pump fail. When the switch is placed in OFF, the electrical circuit is disabled (refer to CONTROL VALVE AND FLOW LIMITER (POWER TRANSFER