PFCS Brakes (R SYS) T/R S Sample valve From RSVR servicing Heat exchanger ACMP filter module GND SVC RTN disk SYS pressurized XDCR Temp XDCR ACMP EDP Pressurized XDCR GND SVC pressurized disk RLF valve RSVR pressurized SW Return filter module RSVR pressurized module EDP filter module EDP supply shutoff valve RSVR pressurized shutoff valve Drain valve RSVR pressurized relief valve RSVR temperature XDCR Pressurized air Supply Pressure Return Depress solenoid valve Temperature XDCR Pressurized  XDCR Figure 12-67.  Right hydraulic system of a Boeing 777. A left system is similar. pressurization module and the reservoir. The ACMP and EDP  filter modules each have a pressure transducer to measure  pump output pressure. A temperature transducer is installed in  the case drain line of each filter module and measures pump  case drain fluid temperature. A system pressure transducer  measures hydraulic system pressure. A pressure relief  valve on the EDP filter module protects the system against  overpressurization.  [Figure 12-67] The hydraulic system reservoir of the center system contains  the hydraulic fluid supply for the hydraulic pumps. The  reservoir is pressurized by bleed air through a reservoir  pressurization module. The reservoir supplies fluid to the  ADPs, the RAT, and one of the ACMPs through a standpipe.  The other ACMP gets fluid from the bottom of the reservoir.  The reservoir also supplies hydraulic fluid to the landing gear  alternate extension system. The center hydraulic system supplies pressurized hydraulic  fluid to operate these systems.  [Figure 12-68] The ACMPs are the primary pumps in the center hydraulic  system and are normally turned on. The ADPs are the demand  pumps in the center system. They normally operate only  when the center system needs more hydraulic flow capacity.  The RAT system supplies an emergency source of hydraulic  power to the center hydraulic system flight controls. A  reservoir quantity transmitter and temperature transducer  are installed on the reservoir. A hydraulic reservoir pressure  switch is installed on the pneumatic line between the reservoir  and the reservoir pressurization module. Reservoir Center Hydraulic System •  Nose landing gear actuation •  Nose landing gear steering •  Alternate brakes •  Main landing gear actuation •  Main landing gear steering •  Trailing edge flaps •  Leading edge slat •  Flight controls  12-45