73-21-14
 ALL  ú ú C01 Page 408 ú Nov 15/94
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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CFM56 ENGINES
737-300/400/500/ /MAINTENANCE MANUAL ////////////////////////
FUEL FLOW INDICATING SYSTEM - DESCRIPTION AND OPERATION
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 1.  General
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 A.  The fuel flow indicating system gives a visual indication of the fuel flow rate and fuel used for each engine.
 2.  Fuel Flow Transmitter (Fig. 1)
_____________________
 A.  The rate of fuel flow to each engine is measured by a fuel flow transmitter found on each engine on the left side of the fan case, just above the transfer gearbox (TGB).
 3.  Fuel Flow Indicator (Fig. 2)
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 A.  Fuel flow (FF) indication is displayed by a combination fuel flow/fuel used indicator (one for each engine) found on the pilot's center instrument panel.
 B.  Analog Fuel Flow Indicators
 (1)  
The fuel flow rate is displayed as graduations around the circular face of the dial and also by a digital display counter in the indicator. Total fuel used is displayed by the same digital display counter when the FUEL switch is put to the USED position.

 (2)  
The light for the fuel flow indicator is inside the indicator. The indicator is made of a 2 inch diameter case. The electrical connector to the indicator is at the rear of the indicator case.

 (3)  
The FUEL switch permits the digital display for the fuel used to be set back to the zero position when the FUEL switch is put in the RESET position.

 C.  Digital Fuel Flow Indicator on the Primary Engine Instrument System (EIS) Display
 (1)  
The fuel flow rate is displayed by the position of the yellow line on the outside of the circular dial display and by a digital display counter in the dial display. Total fuel used is displayed by the same digital counter when the fuel used PUSH button is pushed.

 (2)  
The indication is displayed in the lower area of the primary engine display. The electrical connector to the indicator is with a plug at the rear of the engine display unit.

 (3)  
The FUEL USED RESET button permits the digital display for fuel used to be put in the zero position when the button is pushed.

 D.  The fuel flow indicator displays fuel flow rates of 280 to 12,000 pounds per hour on indicators in pounds or 127 to 5,500 kilograms per hour on indicators in kilograms.
 4.  Operation (Fig. 3)
_________
 A.  The fuel flow transmitter uses the angular momentum of a rotor to measure the mass flow rate. It is made to minimize the drop in fuel pressure across the transmitter. External power is not necessary.
 (1)  
Fuel goes in the transmitter and flows to a swirl generator. The swirl generator causes the fuel to swirl around or turn as the fuel goes through the angled fins (Fig. 4).

 (2)  
The swirling fuel causes the rotor to turn. The rotor has two magnets attached to its surface. One magnet on the rotor induces a start pulse in a coil each time the magnet passes the coil.

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 73-31-00
 ALL  ú ú C03 Page 1 ú Nov 12/00
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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CFM56 ENGINES
737-300/400/500/ /MAINTENANCE MANUAL ////////////////////////

FUEL FLOW ELECTRICAL CONNECTOR D830
FUEL OUTLET
FWD

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CFM56 ENGINES
737-300/400/500/ /MAINTENANCE MANUAL ////////////////////////
SEE SEE
FUEL FLOW INDICATORS WITH THE FUEL USED DIGITAL DISPLAY IN KILOGRAMS

A 
B

1
READS FUEL FLOW ON SOME AIRPLANES
Fuel Flow Indicator Location
Figure 2 (Sheet 1)

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