39 Questions
What is the purpose of adjusting the engine signal in a testing mode?
To reduce the overspeed setting by a fixed amount
Why is it important to have a 2nd person standing by during full tests after major overhauls?
To manually shut down the engine in case it runs away
What is the significance of having full test point manifolds at an easily accessible point?
Makes testing all alarm and shut-down points much easier
What is the purpose of the automatic valve in an air start system?
To isolate the compressed air from the engine and only open when there is a signal to initiate a start.
How does the pilot air signal the automatic valve to open in an air start system?
When a start signal is applied, the pilot air signal the valve to open.
What is the function of the non-return valve in an air start system?
To prevent the reverse flow of compressed air into the system.
Why do many manufacturers opt for air start valves direct into individual cylinders for diesel engines?
To provide a very capable system that delivers timed air into the cylinders to sequentially turn the engine over to start.
What is the potential risk associated with air start systems if key equipment fails?
The potential for explosions to take place.
How can an air start system be tested to ensure it trips at a lower speed?
By fitting it with a test weight.
What are the advantages of using air start valves directly into individual cylinders?
Precise control over engine starting and sequential turning over of the engine.
What is the preferred method to avoid running a large engine in overspeed conditions?
Fitting the device with a test weight to trip at a lower speed.
How does the air start system drawing help in understanding potential areas of failure?
By visualizing the system design and components where failure may occur.
What are two basic shut-down sensors that marine engines typically come with?
Low Lubricating Oil Pressure and High Cooling Water Temperature
Name two other shut-down sensors that can be fitted to marine engines.
High Exhaust Temperature and High Lubricating Oil Temperature
What is the purpose of a 'Falling Pressure' switch in the context of marine engines?
To monitor Low Lubricating Oil pressure
Describe how the 'Falling Pressure' switch operates when the pressure falls below a set point.
Pressure falls in bellows, spring forces 'Trip lever' down, 'Trip lever' releases the 'Reset lever', and 'Electrical contact' opens to shut down the machine.
What is a bi-metallic strip used for in the context of temperature sensing?
A bi-metallic strip is used to sense temperature changes.
Why is it suggested to concentrate on simpler electro-mechanical devices for examination purposes?
It is often better to concentrate on simpler electro-mechanical devices for examination purposes.
What is the purpose of a Crankcase Oil Mist Detector?
To detect oil mist in the crankcase and prevent potential hazards.
Why are safety sensors like Pressure Sensing and Temperature Sensing essential in marine engines?
Pressure Sensing and Temperature Sensing are essential for monitoring critical parameters in marine engines.
What is the role of a Hydraulic Governor in engine protection?
A Hydraulic Governor helps in controlling the engine speed to prevent overspeed.
What is the purpose of the bi-metallic strip in the context described?
To move and open the electrical contact to shut down the machine in case of high temperatures
Why are electronic overspeed devices preferred over mechanical ones?
Electronic controls allow testing without physically running the engine at an overspeed condition.
What happens when the main pin in the mechanical overspeed trip mechanism strikes the plunger?
The plunger operates the trip mechanism.
How does the auxiliary weight behave when the speed of the shaft increases?
The aux weight is pulled outwards due to centrifugal force.
What is the function of the U-Lock Staple in the mechanical overspeed trip mechanism?
To hold the adjusting nut in place.
Why is it important to remove the test setting after conducting an overspeed test on the engine?
To prevent the engine from tripping during normal operation.
How do electronic overspeed devices eliminate the need for physically running the engine at an overspeed condition during testing?
By allowing the overspeed to be temporarily reduced while manually increasing the engine's speed.
What initiates the movement of the main pin in the mechanical overspeed trip mechanism?
The force from the auxiliary weight overcoming the spring.
Describe the role of the adjusting nut in the mechanical overspeed trip mechanism.
To control the position of the main pin.
What is the purpose of the feedback link in a governor system?
To increase tension of the speeder spring and return the pilot valve to neutral position.
Define 'Gain' in the context of governors.
Gain represents the amplification or reaction of the governor to a change in engine speed.
How does an electronic governor differ from a mechanical governor?
Electronic governors provide finer control and can be interlinked with specific load profiles.
What components are involved in an electronic governor system?
Fuel rack, Servo, Emergency stop solenoid, Speed setting signal, Overspeed, Low lubrication oil, High temperature, Control unit, Comparator, Sensors, Speed sensors.
How does the comparator contribute to the operation of an electronic governor system?
The comparator uses signals to provide a final output speed to the control unit for adjustments.
What is the role of the actuator in an electronic governor system?
The actuator receives signals from the speed control and adjusts the fuel supply based on power and speed sensing.
Why is it important for an electronic governor system to sense overspeed?
To prevent the engine from operating beyond safe speed limits and causing potential damage.
How do voltage and current transformers contribute to the functioning of an electronic governor system?
They measure power output to provide data for speed control adjustments.
Explain the purpose of paralleling lines to other units in an electronic governor system.
To synchronize the operation of multiple units for efficient power generation.
Study Notes
Safety Sensors
- Marine engines typically come with basic shut-down sensors, including low lubricating oil pressure, high cooling water temperature, and overspeed.
- Additional shut-down sensors can be fitted, including high exhaust temperature, high lubricating oil temperature, and low cooling water pressure.
Pressure Sensing
- A "Falling Pressure" switch can be used to detect low lubricating oil pressure.
- The switch operates by a spring forcing a trip lever down, releasing a reset lever, which opens an electrical contact, shutting down the machine.
Temperature Sensing
- A bi-metallic strip can be used to detect high cooling water temperature.
- Overspeeding an engine incorrectly may cause damage.
Overspeed
- Electronic systems can test overspeed without actually overspeeding the engine.
- The engine speed can be electronically adjusted to reduce the overspeed setting by a fixed amount.
- Full overspeed testing requires the engine to be run up to the full overspeed value and must be done with caution.
Air Starting Systems
- Compressed air is used to start the engine in air starting systems.
- Air start valves directly inject air into individual cylinders to turn the engine.
- The system has potential risks of explosion if key equipment fails.
Hydraulic Governor
- The hydraulic governor regulates engine speed by adjusting fuel supply.
- The servo piston is connected to the fuel rack, which reduces fuel supply when the engine speed increases.
- The feedback link moves down, increasing the tension of the speeder spring, which moves the pilot valve back to the neutral position.
Electronic Governor
- Electronic governors sense speed changes and alter fuel to react to that change.
- They provide a finer degree of control, especially in main engines, where they can be interlinked with specific load profiles.
- The electronic governor system consists of speed sensors, a comparator, a control unit, and fuel rack servo.
Test your knowledge on safety devices used in marine diesel engines with this quiz. Explore topics such as pressure sensing, temperature sensing, overspeed protection, crankcase explosions, and more.
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