737 Flight Crew Operations Manual
Engines, APU -
Engine System Description
Boeing Proprietary. Copyright © Boeing. May be subject to export restrictions under EAR. See title page for details.
7.20.8 D6-27370-866-EGP
Engine Fuel System
Fuel is delivered under pressure from fuel pumps located in the fuel tanks. The
fuel flows through a fuel spar shutoff valve located at the engine mounting wing
stations. The fuel passes through the first stage engine fuel pump where pressure
is increased. It then passes through two fuel/oil heat exchangers where IDG oil and
main engine oil heat the fuel. A fuel filter then removes contaminants. Fuel
automatically bypasses the filter if the filter becomes saturated. Before the fuel
bypass occurs, the fuel FILTER BYPASS alert illuminates on the fuel control
panel. The second stage engine fuel pump adds more pressure before the fuel
reaches the hydro mechanical unit (HMU). To meet thrust requirements, the EEC
meters fuel through the HMU.
The spar fuel shutoff valve and engine fuel shutoff valve allow fuel flow to the
engine when both valves are open. The valves are open when the engine fire
switch is in and the start lever is in IDLE. Both valves close when either the start
lever is in CUTOFF or the engine fire switch is out. SPAR VALVE CLOSED and
ENG VALVE CLOSED lights located on the overhead panel indicate valve
position.
Fuel flow is measured after passing through the engine fuel shutoff valve and is
displayed on the display unit. Fuel flow information is also provided to the FMS.
Engine Oil System
Oil from the individual engine tank is circulated under pressure, through the
engine to lubricate the engine bearings and accessory gearbox. The oil quantity
indicator, oil temperature indicator, oil pressure indicator and LOW OIL
PRESSURE alert are all located on the display unit.
The oil system is pressurized by the engine driven oil pump. Oil from the pump,
goes to the engine bearings and gearbox. Sensors for the oil temperature indicator,
oil pressure indicator and LOW OIL PRESSURE alert are located downstream of
the oil pump prior to engine lubrication.
Oil is returned to the oil tank by engine driven scavenge pumps. From the
scavenge pumps oil passes through a scavenge filter. If the filter becomes
saturated with contaminants, oil automatically bypasses the filter. Prior to the oil
bypassing the scavenge filter, the OIL FILTER BYPASS alert illuminates on the
upper display unit.
Prior to returning to the oil tank, the oil passes through the main engine oil cooler
where it is cooled by engine fuel to maintain proper oil temperature.
September 26, 2013
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