737 Flight Crew Operations Manual
Hydraulics -
System Description
Boeing Proprietary. Copyright © Boeing. May be subject to export restrictions under EAR. See title page for details.
D6-27370-866-EGP 13.20.3
Hydraulic fluid used for cooling and lubrication of the pumps passes through a
heat exchanger before returning to the reservoir. The heat exchanger for system A
is located in main fuel tank No. 1 and for system B is in main fuel tank No. 2.
CAUTION: Minimum fuel for ground operation of electric motor-driven
pumps is 760 Kgs in the related main tank.
Pressure switches, located in the engine–driven and electric motor–driven pump
output lines, send signals to illuminate the related LOW PRESSURE light if pump
output pressure is low. A check valve, located in each output line, isolates the
related pump from the system. The related system pressure transmitter sends the
combined pressure of the engine–driven and electric motor–driven pump to the
related hydraulic system pressure indication.
System A Hydraulic Leak
If a leak develops in the engine–driven pump or its related lines, a standpipe in the
reservoir prevents a total system fluid loss. With fluid level at the top of the
standpipe, the reservoir quantity displayed indicates approximately 20% full.
System A hydraulic pressure is maintained by the electric motor–driven pump.
If a leak develops in the electric motor–driven pump or its related lines, or
components common to both the engine and electric motor–driven pumps, the
quantity in the reservoir steadily decreases to zero and all system pressure is lost.
System B Hydraulic Leak
If a leak develops in either pump, line or component of system B, the quantity
decreases until it indicates approximately zero and system B pressure is lost. The
system B reservoir has one standpipe which supplies fluid to both the engine–
driven pump and the electric motor–driven pump. However, with fluid level at the
top of the standpipe, fluid remaining in the system B reservoir is sufficient for
power transfer unit operation.
A leak in system B does not affect the operation of the standby hydraulic system.
Power Transfer Unit
The purpose of the PTU is to supply the additional volume of hydraulic fluid
needed to operate the autoslats and leading edge flaps and slats at the normal rate
when system B engine–driven hydraulic pump volume is lost. The PTU uses
system A pressure to power a hydraulic motor–driven pump, which pressurizes
system B hydraulic fluid. The PTU operates automatically when all of the
following conditions exist:
• system B engine–driven pump hydraulic pressure drops below limits
• airborne
• flaps not up.
September 26, 2013
To Next Page
Loading...
