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-A pre-loaded spring, which opposes the force produced by the flyweights, and is calibrated to the overspeed setting.
Overspeed governor test.
At each engine start, N2 increases and the flyweight device applies an upward force on the bottom of the governor pilot valve.
As the governor pilot valve continues to move up, Psf pressure is ported to one side of a piston, which is connected to a micro-switch dedicated to the ECU starting logic.
The micro-switch informs the ECU that the governor system is in operation.
Below 38-45% N2 speed, the micro-switch is open.
Above 45% N2, the switch closes, confirming that the overspeed governor system is in operation.
The switch remains closed until N2 drops below 45%.

EFG

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CTC-201-269-01
EFFECTIVITY
73-21-18 Page 25
ALL CFM56-5B ENGINES FOR A319-A320-A321
ENGINE SYSTEMS Jan 03

CFMI PROPRIETARY INFORMATION
CFM56-5B TRAINING MANUAL
EFG
HYDROMECHANICAL UNIT
Overspeed Governor System in-speed condition.
During regular engine operation, the force of the flyweight device is not strong enough to overcome the force of the pre-loaded spring.
In this in-speed condition, the pilot valve continues to send Psf and Pb fuel pressures to the Delta P pilot valve in order to modulate the by-pass valve for normal operations.

EFG

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CTC-201-267-01
EFFECTIVITY

73-21-18 Page 27
ALL CFM56-5B ENGINES FOR A319-A320-A321
ENGINE SYSTEMS Jan 03

CFMI PROPRIETARY INFORMATION
CFM56-5B TRAINING MANUAL
EFG

HYDROMECHANICAL UNIT
Overspeed Governor System in an overspeed condition.
When N2 reaches 98%, the flyweight force equals the spring force.
As speed continues to increase, the pilot valve moves up, slightly restricting Psf  flow to the Delta P regulator.
When speed reaches the overspeed value of 106%, the Psf supply to the Delta P valve is reduced to Pb and this causes the by-pass valve to stroke further open.
More fuel is by-passed, decreasing fuel flow to the FMV and, therefore, less fuel is available for combustion.
As a result, N2 decreases until it is below the overspeed value.
When N2 returns to the normal range, the preloaded spring can now oppose the force of the flyweights, so the pilot valve moves back down and the pressure ported to the Delta P regulator is returned to Psf.

EFG

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CTC-201-268-01
EFFECTIVITY
73-21-18 Page 29
ALL CFM56-5B ENGINES FOR A319-A320-A321
ENGINE SYSTEMS Jan 03

CFMI PROPRIETARY INFORMATION
CFM56-5B TRAINING MANUAL

EFG

HYDROMECHANICAL UNIT

Pressurizing and shut-off valve.
During engine start, the pressurizing and shut-off valve establishes a minimum Psf pressure to ensure proper operation of the regulators, and piston force margins.
　
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