System consists of a single reservoir . Hydraulic power is supplied
to the A system from two engine driven pumps fitted to engines No1 and
No2 . The pump switches control solenoid operated blocking valves, with
the switches on, normal pump output is supplied to the system. A small
portion of the fluid that enters the pump is circulated through the
pump case for cooling and lubrication. As long as the engines are operating
regardless of the blocking valve position this small amount of fluid
leaves the pump and is cooled by a heat exchanger in the No3 fuel tank
heat exchanger before being returned to the system.
fluid shutoff valves controlled by there respective switches control
the fluid in the engine pump supply lines, when closed fluid flow to
the pump is isolated. (includes lubricating and cooling fluid). pulling
the fire switch on engine 1 or 2 will close these shutoff valves, the
fire switch also deactivates the low pressure warning light.
System A and therefore system B and stand by reservoirs are pressurized
by engine bleed air from engines 1 & 2 this is applied to the reservoir
to ensure a positive supply of fluid to the pumps.
A balance line connects the system A reservoir to the system B reservoir
at a level of 2.5 gall.
A system supplies the heavy
load items landing gear, trailing edge flaps.
Fluid Quantity................4.4 Gall (gear down)
................3.8 Gall (gear up)
™it's normal to see a reduction in the fluid quantity indication in
flight, due to the cold soak characteristics of the system
System Pressure............2,800 - 3100 PSI (red line @ 3,500)
Balance line to "B" system...........2.5 Gall
Operating time with the "A" fluid SOV closed 5 Min's
™ A system pumps max demand flow rate is 22 gal min 100% N2
Nose Wheel Steering
Trailing Edge Flaps
Leading Edge Devices
"B" system again contains a single reservoir supplying two
electric AC pumps. It's reservoir is more complicated that system "A"
in that it has an auxiliary reservoir separated by a baffle which
is open at the top ("little b"), this is reserved for alternate
extension of the leading edge slats and flaps using stand by hydraulic
power (more about that later).
Each pump is controlled by it's individual selection switch, with the
switch ON normal hydraulic output pressure is provided to the system.
As in the "A" system a portion of the fluid is used for cooling
and lubrication of the pump but is returned via a heat exchanger in
the no1 fuel tank. if the pressure falls below the preset level a warning
light will illuminate, sensors monitor the fluid temperature and if
activated will bring on an overheat light. A relay in the overheat sensing
circuit will cause the overheat light to go out when the affected pump
is turned off. A simplified view of the system is the same as the above
diagram but with no blocking valve or shut off valve (items 2 &
Fluid Quantity....................Full if system "A" quantity
over 2.5 gall
System Pressure............2,800 - 3100 p.s.i (red line @ 3,500)
Baffle level (little B)............1.1 gall
Do not operate a system "B" pump with less than 1,300
lbs in fuel tank No1
Any one hydraulic system "B" pump should not be operated more
than 5 times in 5 min's. After this period the pump must be left on
for 5 min's or off for 30 min's.
The standby system reservoir supplies fluid to an AC electric motor
driven pump. Positioning the standby rudder switch or the alternate
flap master to on will provide power to the standby motor, which in
turn supplies fluid pressure to the standby power module. System pressure
is indicated by a light. There is a overheat sensing to monitor fluid
temperature which will illuminate the overheat light for the standby
Fluid Quantity...............0.3 gall
System pressure........... 2,200 psi @ 1.14 gall per min for leading
edge devices ( the is no pressure gauge for the stand-by system only
a green light.
............ 2,975 to 3,075 @ 3 gll per min for lower rudder
Lower Rudder Stand-By Actuator
Leading Edge Devices (Extension Only)
Positioning the standby rudder switch to on , the system "A"
rudder power switch is selected off. With "A" system off hydraulic
fluid is isolated from the lower rudder power unit, standby system pressure
repositions a selector valve to allow the standby system to power the
lower rudder standby power control unit.
Positioning the alternate flaps master switch on arms the alternate
flap switches (2). Moving either switch to down opens the leading edge
flaps and slats sov. The standby system pressure then drives a hydraulic
motor portion of a pump assembly. The pump portion of this assembly
uses fluid from "little b" to extend the leading edge devices.