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Location of the Fuel Return Valve on the Engine Figure 013
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B. Description
(Ref. Fig. 014)
(1) The rectangular-shaped FRV (starting from top and clockwise) has 6 fuel nipples for connection with the tubing which follows:
- Fuel return line to the fuel tank (WRT)
PRE SB CFM 73-0096
- Shut-off signal line from the HMU (P Stop)
END OF PRE SB CFM 73-0096
POST SB CFM 73-0096
- Bypass line to the fuel pump LP stage (CLP)
END OF SB CFM 73-0096
- Line from the fuel pump HP stage (PSF)
- Cold fuel line from the fuel pump LP stage (CLP)
- Hot fuel line from the IDG oil cooler (HLP)
- Fuel drain line.
(2) The FRV has also 2 electrical receptacles for connection with the channels A and B of the ECU.
C. Operation
(Ref. Fig. 015)
(1) The fuel return valve controls 2 flow levels :
(a) The first level recirculates 500 kg.h (1100 lb.h) including 300 kg.h (726 lb.h) of hot fuel and 200 kg.h (440 lb.h) of cold fuel.
(b) The second level recirculates 1000 kg.h (2203 lb.h) including 600 kg.h (1320 lb.h) of hot fuel and 400 kg.h (881 lb.h) of cold fuel.
(2) The mixing of the recirculated fuel is such that its temperature is maintained below 100 deg.C (212 deg.F) continuously and 110 deg.C (230 deg.F) transiently. Both levels of the fuel return valve are controlled by the ECU based on the engine oil temperature value:
- On ground: Only the first level is selected when engine oil temperature (TEO) is greater or equal to 90 deg.C (194 deg.F)
- In flight
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Description of the Fuel Return Valve
Figure 014
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R R Operation of the Fuel Return Valve Figure 015 (SHEET 1)
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R R Operation of the Fuel Return Valve Figure 015 (SHEET 2)
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The first level is selected when TEO is greater or equal to 90 deg.C (194 deg.F) The second level is selected when TEO is greater or equal to 95 deg.C (203 deg.F)
PRE SB CFM 73-0096
(3) The fuel is not recirculated when the FRV receives an HMU hydraulic signal at the engine shutdown or when the ECU does not command first or second level of recirculated fuel if any of the following conditions is met:
- N2 less than 50 percent
- measured fuel flow greater than 5520 lb.h (2504 kg.min)
- when the ECU receives the inhibition signal to shut off the FRV
END OF PRE SB CFM 73-0096
POST SB CFM 73-0096
(4) The fuel is not recirculated when the ECU does not command first or second level of recirculated fuel if any of the following conditions is met:
- N2 less than 50 percent
- measured fuel flow greater than 5520 lb.h (2504 kg.min)
- when the ECU receives the inhibition signal to shut off the FRV
END OF SB CFM 73-0096
(5) The shut off piston of the valve is equipped with a dual position switch to provide closed/not closed indication. These position switch indications are processed by the ECU.
R **ON A/C 001-049, 051-099, 101-105, 151-199, 201-211,
7. Burner Staging Valve
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A. General (Ref. Fig. 016) The purpose of the Burner Staging Valve (BSV) is to deliver fuel to either all 20 fuel nozzles, or every other fuel nozzle (10 total) as commanded by the ECU. Fuel passes directly through the BSV manifold/mounting bracket to 10 fuel nozzles which are always on when the engine is in operation.
NOTE : With the introduction of 5BK ECU software, the BSV system is no
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longer commended or recognized by the ECU.
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Location of the Burner Staging Valve
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