Answer EKM Question 30
Q30. With reference to bridge control of a large slow propulsion engine;
A. How starting and reversing achieved;
B. Investigate and propose remedial action if the engine,
(I) fails to turn on air;
(II) turns on air but fails to fire on fuel;
(III) fails to reverse.
Answer: A. Explain how starting and reversal achieved.
- For large propulsion engines the Bridge Control is achieved by using the telegraph to select the desired speed and direction.
- When the bridge telegraph is placed in Stop, the fuel is prevented from injecting as the fuel pump puncture valves are energised.
- When the bridge telegraph is moved to an ahead command, the air start and fuel cams are placed in the required direction, and the start command is given. This will admit starting air to the engine. Once the engine is turning above the starting speed, the air is closed and fuel is admitted.
- The quantity of fuel admitted will depend on the position of the telegraph handle, i.e. slow ahead, full ahead, etc.
- When the bridge telegraph is moved to an astern direction, the air start and fuel cams are reversed. Once the air start is reversed, the engine will start as detailed for the ahead start.
B. Describe the investigation and remedial action required action required if the engine
I. fails to turn on air;
- Low air bottle pressure or airline valves may be shut, Air bottle isolating v/v or automatic valve or distributor malfunction.
- Control air valves faulty or less control air pressure.
- Starting air automatic valve Jammed,
- Reversing has not taken place completely.
- Control valves for fuel or 'Start' is not in its end position.
- Bursting diaphragm on start 'airline damaged.
- Fuel lever on manoeuvring stand not on remote mode.
- Not sufficient spring air pressure to shut the exhaust valve, thereby causing loss of compression.
- Auxiliary/blower not running or not on 'AUTO' mode.
- No oil pressure due to exhaust V/V being open or insufficient spring air pressure.
- Start air disiributor has not activated Its end stop valve.
- Start air distributor piston is sticking or incorrectly adjusted or the control valve is sticking.
- Cylinder start air valves are defective or sticky.
II. Turns on air but fails to fire on fuel;
- In B&W engines, the puncture valves are not, properly vented.
- Fuel regulating linkage jammed or held back by the stop Cylinder
- Governor is defective and does not release the fuel linkage, or there is no boost air to governor.
- Rotary valve of the rotation direction safeguard is sticking.
- Shut down of fuel pumps.
- Fuel filter is blocked or fuel pump index is too low.
- Pre-set control air signal to the governor is too low.
- Check for any shut-downs still active. The shutdown panel would be examined, and if a trip is active the cause would be investigated and system made operational.
III. Fails to reverse
- Start air valve for that unit may be sticking, the remedy is to give a kick in the opposite direction and then switch back to the desired direction.
- The reverse control valve is jammed.
- The coil of the solenoid valve for the desired direction or rotation does not get voltage.
- Control air signal for desired direction of rotation does not reach the engine. Loosen piping and check the air route or the defective valve.
- The reversing servo motor of the fuel or start air distributor is jammed or gets stuck before reaching a new end position due to insufficient oil pressure, therefore the engine turns on air but no fuel is released as the rotation direction safeguard blocks it.
- If the engine is running in one direction and reversed, the propeller motion still continues therefore more air and fuel is required for starting against the propeller force.
- The propeller may tend to turn the engine in the original direction i.e opposite to the given movement, there for the rotational direction safeguard blocks the fuel.
Answer: A. Explain how starting and reversal achieved.
- For large propulsion engines the Bridge Control is achieved by using the telegraph to select the desired speed and direction.
- When the bridge telegraph is placed in Stop, the fuel is prevented from injecting as the fuel pump puncture valves are energised.
- When the bridge telegraph is moved to an ahead command, the air start and fuel cams are placed in the required direction, and the start command is given. This will admit starting air to the engine. Once the engine is turning above the starting speed, the air is closed and fuel is admitted.
- The quantity of fuel admitted will depend on the position of the telegraph handle, i.e. slow ahead, full ahead, etc.
- When the bridge telegraph is moved to an astern direction, the air start and fuel cams are reversed. Once the air start is reversed, the engine will start as detailed for the ahead start.
B. Describe the investigation and remedial action required action required if the engine
I. fails to turn on air;
- Low air bottle pressure or airline valves may be shut, Air bottle isolating v/v or automatic valve or distributor malfunction.
- Control air valves faulty or less control air pressure.
- Starting air automatic valve Jammed,
- Reversing has not taken place completely.
- Control valves for fuel or 'Start' is not in its end position.
- Bursting diaphragm on start 'airline damaged.
- Fuel lever on manoeuvring stand not on remote mode.
- Not sufficient spring air pressure to shut the exhaust valve, thereby causing loss of compression.
- Auxiliary/blower not running or not on 'AUTO' mode.
- No oil pressure due to exhaust V/V being open or insufficient spring air pressure.
- Start air disiributor has not activated Its end stop valve.
- Start air distributor piston is sticking or incorrectly adjusted or the control valve is sticking.
- Cylinder start air valves are defective or sticky.
II. Turns on air but fails to fire on fuel;
- In B&W engines, the puncture valves are not, properly vented.
- Fuel regulating linkage jammed or held back by the stop Cylinder
- Governor is defective and does not release the fuel linkage, or there is no boost air to governor.
- Rotary valve of the rotation direction safeguard is sticking.
- Shut down of fuel pumps.
- Fuel filter is blocked or fuel pump index is too low.
- Pre-set control air signal to the governor is too low.
- Check for any shut-downs still active. The shutdown panel would be examined, and if a trip is active the cause would be investigated and system made operational.
III. Fails to reverse
- Start air valve for that unit may be sticking, the remedy is to give a kick in the opposite direction and then switch back to the desired direction.
- The reverse control valve is jammed.
- The coil of the solenoid valve for the desired direction or rotation does not get voltage.
- Control air signal for desired direction of rotation does not reach the engine. Loosen piping and check the air route or the defective valve.
- The reversing servo motor of the fuel or start air distributor is jammed or gets stuck before reaching a new end position due to insufficient oil pressure, therefore the engine turns on air but no fuel is released as the rotation direction safeguard blocks it.
- If the engine is running in one direction and reversed, the propeller motion still continues therefore more air and fuel is required for starting against the propeller force.
- The propeller may tend to turn the engine in the original direction i.e opposite to the given movement, there for the rotational direction safeguard blocks the fuel.
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