40 Questions
What happens to the paralleling valve when the engine reaches 16% RPM?
It closes the path of fuel flow between the secondary and primary pump elements.
Why does the fuel pump go into parallel mode during engine starting?
To maximize fuel pump volume.
What happens when the back pressure is felt due to the closed paralleling valve?
The secondary pump check valve closes.
At what pressure does the secondary pump pressure switch close?
150 PSI
Why does a cockpit light illuminate when the secondary pump pressure switch closes?
To indicate that the pump is in parallel mode.
What is the purpose of the low pressure fuel filter in the fuel flow path?
To remove impurities from the fuel.
Why does each element have a separate fuel flow path in parallel mode?
To maximize fuel pump volume.
What initiates the closure of the paralleling valve?
Engine reaching 16% RPM
What happens when the engine speed governor reacts to speed variations?
Moves the roller cage against the multiplying linkage
What is the role of the pilot servo valve rod in governing engine speed?
Affects roller cage position through the multiplying linkage
How does the spring cap react during acceleration when the power lever is moved upwards?
Slides down the pilot servo valve rod and compresses the flyweight speeder spring
What function does the pilot servo valve serve in controlling air/fuel ratio changes?
Slows the movement of the pilot servo control rod
When the pilot valve rod moves downwards, what happens to the roller?
Moves down the incline plane and to the left
What is the purpose of compressing the flyweight speeder spring during acceleration?
Forcing the flyweights to an under-speed condition
How does the roller cage position affect engine operation?
It returns the engine to a steady governed state
Which component helps prevent sudden air/fuel ratio changes in engine operation?
The pilot servo valve
What differentiates the variable displacement pump from the constant displacement gear type pump?
The variable displacement pump changes pump displacement to meet varying fuel flow requirements without changing speed.
How is the pumping action produced in a variable displacement pump?
By moving the rotor to impart a reciprocating motion to the plungers.
How is the action of a variable displacement pump infinitely varied?
By altering the inclination of a cam-plate to change the length of plunger stroke.
What causes variations in the movement of the servo piston in a variable displacement pump?
Variations in pressure difference across the servo piston.
How does a fuel control unit regulate pump pressure and delivery in a variable displacement pump?
Automatically and accurately when integrated with a variable flow pump.
What is mechanically linked to the cam-plate in a variable displacement pump?
Servo piston
What is biased by springs to give full stroke position of the plungers in a variable displacement pump?
Servo piston
What effect does varying fuel servo pressure have on a servo piston in a variable displacement pump?
Causes corresponding variations in cam-plate angle.
What happens to the burner pressure as the engine slows down?
It decreases
What does the multiplying linkage and roller mechanism do in response to the decrease in burner pressure?
Moves further to the right
What happens when the new flyweight force reaches equilibrium with the speeder spring force?
The flyweights return toward an upright position
What is the purpose of allowing the engine to stabilize at idle before shutdown?
To enable gradual turbine cooling
Why is it essential to follow a shutdown procedure on a simplified fuel control unit?
To prevent overheating of the engine
What is the role of the fuel shut-off valve during the shutdown process?
It remains closed
How do the flyweights position themselves after responding to a speed change?
Return toward an upright position
Why does burner pressure decrease as the engine slows down?
To decrease fuel flow
What does a supervisory electronic engine control system do?
Receive information from various engine sources and limit fuel flow
Which signals does the control amplifier in the system receive?
Turbine gas temperature (TGT) and two compressor speed signals (N1 and N2)
At what point does the electronic circuit in the control system start to function as a fuel limiting device?
Near full power
How does the pressure regulator in the installation regulate fuel flow?
By reducing fuel flow to the spray nozzles
Which signals does the fuel flow regulator in the system receive?
N3 compressor speed, gas path pressure, and power lever position
What role does the control amplifier play in the system?
Receives signals from turbine gas temperature and compressor speeds
When does the pressure regulator reduce fuel flow to the spray nozzles?
When predetermined TGT and compressor speed values are reached
What triggers the electronic circuit to act as a fuel limiting device?
Near full power, predetermined TGT, and compressor speed values being reached
Learn about the operation of the fuel pump below 16% RPM at the DEFENCE AEROSKILLS TRAINING ACADEMY. Understand the parallel mode operation as depicted in Figure 10 and how the paralleling valve functions at different RPM levels.
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