Figure 12-66.  A Boeing 777 hydraulic system. hydraulic fluid to operate the right thrust reverser, flight  control systems, and the normal brake system.  [Figure 12-67]  The hydraulic system reservoirs of the left and right system  contain the hydraulic fluid supply for the hydraulic pumps.  The reservoir is pressurized by bleed air through a reservoir  pressurization module. The EDP draws fluid through a  standpipe. The ACMP draws fluid from the bottom of  the reservoir. If the fluid level in the reservoir gets below  the standpipe, the EDP cannot draw any fluid any longer,  and the ACMP is the only source of hydraulic power. The  reservoir can be serviced through a center servicing point  in the fuselage of the aircraft. The reservoir has a sample  valve for contamination testing purposes, a temperature  transmitter for temperature indication on the flight deck, a  pressure transducer for reservoir pressure, and a drain valve  for reservoir draining.  The EDPs are the primary pumps for the left and right  hydraulic systems. The EDPs get reservoir fluid through the  EDP supply shutoff valves. The EDPs operates whenever the  engines operate. A solenoid valve in each EDP controls the  Reservoir Pumps 12-44 pressurization and depressurization of the pump. The pumps  are variable displacement inline piston pumps consisting of  a first stage impeller pump and a second stage piston pump.  The impeller pump delivers fluid under pressure to the piston  pump. The ACMPs are the demand pumps for the left and  right hydraulic systems. The ACMPs normally operate only  when there is high hydraulic system demand. Pressure and case drain filter modules clean the pressure  flows and the case drain flows of the hydraulic pumps. A  return filter module cleans the return flow of hydraulic fluid  from the user systems. The module can be bypassed if the  filter clogs, and a visible indicator pops to indicate a clogged  filter. The heat exchanger, which is installed in the wing fuel  tanks, cools the hydraulic fluid from ACMP and EDP case  drain lines before the fluid goes back to the reservoir. Filter Module Indication The hydraulic system sensors send pressure, temperature,  and quantity signals to the flight deck. A reservoir quantity  transmitter and temperature transducer are installed on each  of the reservoirs, and a hydraulic reservoir pressure switch  is located on the pneumatic line between the reservoir  Bleed air Supply Pressure Return EDP = Engine driven pump ACMP = AC motor pump ADP = Air driven pump L ACMP C1 ACMP C2 ACMP L ACMP L EDP R EDP Center Left Right LDG GR ALTN Extend DC HYD pump ISLN C1 ADP C2 ADP ISLN SOV Heat exchanger (left main tank) Heat exchanger (right main tank) Heat exchanger (right main tank) SOV return return return Main landing gear actuation LE slats primary drive Main gear steering Nose landing gear actuation Nose wheel steering Tail flight controls Wing flight controls Thrust reverser Tail flight controls Wing flight controls Thrust reverser TE flaps primary drive Tail flight controls Wing flight controls RAT Reservoir fill selector valve Altn/Res brakes Normal brakes