TM  1-1520-240-10            2-6-1 SECTION  VI.  HYDRAULIC SYSTEMS 2-6-1.  Hydraulic Power Supply System. The  hydraulic  power  supply  system  consists  of  three separate systems. They are the No. 1 flight control sy- stem, No. 2 flight control system, and a utility system. Each system includes a variable delivery pump and res- ervoir cooler. In addition, each flight control system has a  power  control  module,  and  the  utility  system  has  a pressure control module. Each flight control system is connected to the utility system by a Power Transfer Unit (PTU). All systems are serviced by a common fill module and are pressurized to prevent pump cavitation. 2-6-2.  Flight Control Systems. The No. 1 and No. 2 flight control systems are identical. they ar parallel in operation, hydraulically separated, and electrically integrated. The flight control system operate at approximately 3,000 psi, which is reduced to 1,500 psi for ILCA operation. They power four upper dual boost actuators (3,000 psi) and four ILCAs (1,500 psi). Each flight control system powers one piston of each actuator. No. 1 flight control system is pressurized by a pump on the forward transmission. No. 2 system is pressurized by a pump on the aft transmission. The power control mod- ules consist of pressure-line and return-line filters. No.1 system power control module is in the forward pylon. No. 2 system power control module is in the aft pylon. The accumulators  dampen  low  frequency  pressure  surges and provide stored hydraulic power for peak loads. The PTU in each system allows ground checkout of the flight control systems with the rotors stopped. Each PTU consists of a pump driven by a hydraulic motor which is pressurized by the utility hydraulic system. The PTU’s are controlled by the PWR XFER 1 and 2 switches on the HYD panel in the overhead switch panel. 2-6-3.  FLT CONTR Switch. The FLT CONTR (flight control) switch is located on the HYD panel in the overhead switch panel (fig. 2-6-1). It is a  three-position  center  locked  switch  labeled  2  ON, BOTH, and 1 ON. this switch can be used to turn off one of the flight control systems, provided the other one is operating. Turning off one of the flight control hydraulic systems disables the corresponding AFCS and causes the remaining AFCS to make full corrections. In addition, the respective AFCS OFF and HYD FLT CONTR caution capsules will illuminate. The FLT CONTR switch shall be set to BOTH during all flight conditions. At BOTH , both solenoid valves are deenergized open and both flight control systems are pressurized. When the FLT CONTR switch is set to 1 ON, the two-way sole- noid valve on No. 2 power control module is energized closed. This causes No. 2 pressure-operated valve to close,  depressurizing  No.  2  system.  When  the  FLT CONTR switch is moved to 2 ON, the two-way solenoid valve  on  No.  2  power  control  module  is  deenergized open, and No. 2 system is pressurized. Simultaneously, No. 1 solenoid valve closes and No. 1 system is turned off. 2-6-4.  Utility Hydraulic System. The utility hydraulic system supplies hydraulic power to the wheel brakes, power steering actuator, swivel locks, centering cams, ramp actuating cylinders, hydraulic car- go door motor, actuator for the center cargo hook, cargo/ rescue winch control valve, two engine starters. PTU;s and APU start circuit. When the APU is running, the utility hydraulic system is pressurized by an APU driven pump. When the APU is not running and the rotors are turning, the utility hydraulic system is pressurized by an aft trans- mission driven pump. The utility hydraulic system incorporates a pressure con- trol module which isolates utility subsystems from each other. When a failure occurs in one utility hydraulic sub- system, the remaining subsystems continue to operate normally if the BRK STEER and RAMP PWR switches in the cockpit are set to OFF. The APU starting subsystem of the utility hydraulic sys- tem includes three accumulators which accelerate the APU to start, maintain reservoir pressure throughout the start cycle, and control operation of the APU motor pump. The APU starting subsystem also includes a two-stage hand pump for charging the APU start accumulators. The APU is normally recharged by the APU motor-pump after the  APU  is  started.  An  additional  accumulator  in  the brake system provides for limited brake operation in the event of utility hydraulic system failure. the steering sys- tem also has an accumulator to keep the swivel locks engaged when the BRK STEER switch is OFF. Normal operating pressure range for the utility hydraulic system is 2500 to 3500 psi. During APU operation pres- sure is increased to approximately 3350 psi for engine starting.  (See  table  2-15-1  for  flight  control  and  utility hydraulic system capacities and fig. 2-15-3 for accumula- tor precharge pressures.) Figure  2-6-1.  Hydraulics Control Panel