The recirculation pressure-holding valve has:
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a valve body
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a poppet valve
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a screwed end
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a spring
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a seal.
The screwed end attaches to the valve body and is locked with a pin. This assembly contains the poppet valve, the seal and the spring. If the fuel pressure is less than 1.07 bar (15.5 psi), the spring keeps the poppet valve in the closed position against the seal.
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C. Recirculation Pressure-Holding Valve 218QM(219QM)
(Ref. Fig. 004A)
The recirculation pressure-holding valve has:
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a valve body
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a poppet valve
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a screwed end
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a spring
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a seal.
The screwed end attaches to the valve body and is locked with a pin. This assembly contains the poppet valve, the seal and the spring. If the fuel pressure is less than 1.07 bar (15.5 psi), the spring keeps the poppet valve in the closed position against the seal.
**ON A/C ALL
If the fuel pressure becomes larger than 1.07 bar (15.5 psi) the poppet valve lifts from the seal. This causes the pressure in the recirculation pipe to decrease to the set pressure. When this occurs, the spring moves the poppet valve to the closed position.
7. Operation/Control and Indicating
________________________________
R **ON A/C 001-049, 051-099, 101-149, 151-199, 201-299, 401-499,
Some of the fuel supply to the engine is used to decrease the temperature of the oil in the IDG. The fuel goes through the IDG heat exchanger to the FRV. The recirculation system then moves the heated fuel along the recirculation pipe and into the wing tank outer cell. The pressure holding valve keeps the fuel in the recirculation pipe to a specified pressure, thus the fuel does not boil. The control of the recirculation system operation is fully automatic. Two temperature sensors (Ref. 28-46-00) in each wing tank send the fuel temperature data to the FLSCU (Ref. 28-46-00). The FLSCU has two computers which are:
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the Fuel Level-Sensing Control Unit 1 (FLSCU1)
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the Fuel Level-Sensing Control Unit 2 (FLSCU2).
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Some of the fuel supply to the engine is used to decrease the temperature of the oil in the IDG. The fuel goes through the IDG heat exchanger to the FRV. The recirculation system then moves the heated fuel along the recirculation pipe where it is joined by cold fuel from the cooling fuel pipe. The cold fuel decreases the temperature of the fuel in the recirculation pipe. The recirculation system then moves the (lower temperature) fuel into the wing tank through holes at the end of the recirculation pipe and the piccolo tube.
The control of the recirculation system operation is fully automatic. A temperature sensor (Ref. 28-46-00) in each wing tank sends the fuel temperature data to the FLSCU (Ref. 28-46-00). The FLSCU has two computers which are:
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the Fuel Level-Sensing Control Unit 1 (FLSCU1)
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the Fuel Level-Sensing Control Unit 2 (FLSCU2).
**ON A/C ALL
The fuel temperature data from the LH wing goes to the FLSCU1, while the fuel temperature data from the RH wing goes to the FLSCU2. Thus the FLSCU1 (together with the No. 1 engine FADEC) (Ref. 73-20-00) controls the recirculation system in the LH wing. The FLSCU2 (together with the No. 2 engine FADEC) controls the recirculation system in the RH wing.
Each FRV controls the fuel flow from the IDG oil cooling system (Ref. 73-10-00) to the recirculation system. It will only open when the related FADEC sends an open signal.
An IDG shut-off level sensor is located in each wing (Ref. 28-46-00). The sensors send fuel level data to the FLSCUs. When the fuel level in the wing tanks reaches a certain level the FLSCUs signal the FADEC to stop the recirculation system.
R **ON A/C 001-049, 051-099, 101-149, 151-199, 201-299, 401-499,
The FLSCU1 or FLSCU2 sends a signal to close the related FRV (through the FADEC) if one of these conditions occur:
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the fuel temperature sensor in the wing tank inner cell sends a high fuel temperature signal (52.5 deg.C (126.50 deg.F) approximately)
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the fuel temperature sensor in the wing tank outer cell sends a high fuel temperature signal (55 deg.C (131.00 deg.F) approximately)
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