Air Systems and Compressors Flashcards
State FOUR reasons for taking too long to fill the main starting air bottles
- Worn Cylinder Liner
- Worn Piston Rings
- Leaking/Open Drain
- Leaking/Open Valves
- Blocked Air Inlet Filters
- Seals Worn
- Incorrectly Seated Valves
State FOUR safety devices fitted to an air starting system of a large marine diesel engine
- Fusible Plug
- Bursting Disc
- Non return Valve
- High Pressure Relief Valve
- High Pressure Cut Off
- Unloader
Describe with the aid of a sketch, a protective device fitted to the water side of the intercooler and aftercooler
INCUDES SKETCH
BURSTING DISC
- This device is fitted and designed as a weak point to rupture and relive the pressure inside before the point the pressure would become dangerous or damage the main body.
Explain why the Bursting Disc is fitted
- To relive pressure build up by bursting and allowing that pressure to escape.
- High pressure can be caused by leaking tubes.
Describe the possible consequence should the Bursting Disc fail to operate
- Pressure can build up to a dangerous level
- Damage to the main body
with reference to air compressors
State how a deterioration in the efficiency would be detected
- Time Taken to Fill will Increase
- Overheating of Compressor
- High Air Temperature
- Large Increase in Running Hours
with reference to air compressors
State FOUR different causes for deterioration in the efficiency of a start compressor
- Worn Piston Rings/Liners
- Leaking Drain Valves
- Loss of Cooling to Inter-cooler/After-cooler
- Insufficient Cooling
- Suction Air Filter Blocked/Restricted
- Valve Malfunctions
with reference to air compressors
Describe a test for establishing performance
(International Association of Classification Societies)
- IACS Regulations, state that it must fill the air bottle to 30bar within 1hr.
1), Start one compressor and note down the time taken to fill to 30bar.
2), Start another compressor and note down the time it also takes to reach 30bar.
3), Compare both times.
4), Should take no longer than 1hr to fill.
with reference to air compressors
State THREE maintenance procedures that maintain their efficiency
- Regular Overhaul of Valves
- Regular Inspection/Cleaning of Filters
- Regular Overhaul of Drains and Unloaders
- Regular Cleaning of Main Body
- Maintaining Good Lubrication
Describe the manual procedure for manual starting of an air compressor
1), Change the mode selector switch to Manual.
2), Check the L.O sump level and ensure its in safe limits.
3), Ensure Inter-stage Drains and the Unloader Valve are Open to prevent load during start-up.
4), Open the Compressor Discharge Valve to allow compressed air to flow.
5), Open the Air Bottle Filling Valve to permit air charging into the receiver.
6), Open the Cooling Water Supply to prevent overheating during operation.
7), Manually Rotate the Compressor Flywheel to check for freeness and no mechanical obstruction.
8), Start the Compressor Motor.
9), Once compressor stabilizes., Close the Inter-stage Drains and Unloader Valve.
10), Monitor Pressure and Temperature.
11), Once air bottle is filled to required pressure, Open Inter-stage Drain and Unloader Valve. (to release moisture).
12, Stop Compressor
State FIVE important safety features fitted to the system
- Pressure Relief Valve
- Bursting Disc
- Unloader
- Fusible Plug
- Non Return Valve
- High Pressure Cut Off
State how a leaking air start valve may be detected when the engine is running
The start air branch pipe local to the affected unit will become hot.
- May Glow Red
- May Smell Burning of Paint
Explain the dangers of allowing a leaking air start valve to persist
- The compressed air may leak into the cylinder.
- If there is oil or unburnt fuel in said cylinder… a start air explosion will occur. Due to the compressed air and oil/unburnt fuel mixing.
Describe 3 methods of reversing an engine
Axial Moving Cams - Uses two sets of cams (Ahead & Astern) these cams are engaged by sliding the camshaft axially but can only be achieved by gear driven camshafts
Moving the Cam Follower - this is done by shifting the cam follower on top of a negative cam profile altering pump timings
Lost Motion - uses a servomotor to rotate the camshaft relative to the crankshaft, altering valve and injection timing for reversal
Explain what is meant by lost motion
Lost motion is the motion lost when rotating the camshaft as the engine is stopped.
