LEC Mechanical and Electrical Systems 3 — Questions and Answers
Question 1: What is the function of the 'alerter' (or vigilance device) on a locomotive?
- Warn of overspeed conditions detected by the speedometer
- Ensure the engineer is alert by requiring periodic acknowledgment (Correct answer)
- Alert dispatchers when the locomotive enters a restricted zone
- Sound a horn automatically at grade crossings
Correct answer: Ensure the engineer is alert by requiring periodic acknowledgment
The alerter requires the engineer to periodically press a button or move a control to confirm alertness; failure to respond triggers a penalty brake application.
Question 2: In a diesel-electric locomotive, what causes 'wheel slip' and how is it initially detected?
- Excessive brake cylinder pressure detected by pressure transducers
- Traction motors drawing unequal current detected by wheelslip relays or sensors (Correct answer)
- Fuel starvation causing uneven power delivery detected by RPM sensors
- Overheated axle bearings detected by hot-box detectors
Correct answer: Traction motors drawing unequal current detected by wheelslip relays or sensors
Wheel slip occurs when traction motor torque overcomes rail adhesion; it is detected by current imbalance between motors or by axle speed sensors.
Question 3: What is the role of the 'main reservoir' in a locomotive's air system?
- Store brake pipe air for emergency applications
- Provide the primary compressed air supply for all pneumatic systems (Correct answer)
- Equalize pressure between the locomotive and train line
- Supply air only to the windshield wipers and horn
Correct answer: Provide the primary compressed air supply for all pneumatic systems
The main reservoir stores compressed air from the compressor and supplies all locomotive pneumatic systems including brakes, controls, and auxiliaries.
Question 4: When a locomotive's cooling water temperature exceeds safe limits, what protective action typically occurs?
- The throttle is automatically advanced to increase fan speed
- The engine automatically reduces power or shuts down to prevent damage (Correct answer)
- The fuel pump is disabled to reduce combustion heat
- The dynamic brakes are applied to reduce locomotive speed
Correct answer: The engine automatically reduces power or shuts down to prevent damage
High coolant temperature triggers a power reduction or engine shutdown to protect the diesel engine from thermal damage.
Question 5: What does 'motoring' mean in locomotive operation terminology?
- Operating the locomotive in dynamic brake mode
- Using traction motors to propel the locomotive forward (Correct answer)
- Starting the diesel engine from shutdown
- Running the locomotive at minimum throttle to maintain speed
Correct answer: Using traction motors to propel the locomotive forward
Motoring describes the mode where traction motors receive electrical power and convert it to mechanical energy to move the locomotive.
Question 6: Which component in the brake system equalizes brake cylinder pressure across all cars when the engineer makes a service brake application?
- Relay valve
- Brake pipe
- Distributing valve (control valve) (Correct answer)
- Equalizing reservoir
Correct answer: Distributing valve (control valve)
The distributing valve (control valve) on each car senses brake pipe pressure reduction and proportionally applies brake cylinder pressure to that car's brakes.
Question 7: What is the purpose of the 'fuel prime' switch or priming pump on a diesel locomotive?
- Increase fuel pressure for high-throttle operation
- Remove air from the fuel system to ensure reliable starting (Correct answer)
- Regulate fuel temperature before injection
- Switch between primary and reserve fuel tanks
Correct answer: Remove air from the fuel system to ensure reliable starting
The fuel prime switch activates a pump to fill fuel lines and remove air, which is necessary for reliable diesel engine starting after shutdown or fuel system work.
LEC Mechanical and Electrical Systems 3
What is the function of the 'alerter' (or vigilance device) on a locomotive?