AUXILIARY MACHINERY
A term applied collectively to all machinery and apparatus forming the non propulsive equipment of a
ship.
- Deck auxiliaries, deck equipment, deck machinery – All machinery used for working the vessel and
handling the cargo: winches, windlass, steering gear, cranes, etc.
- Engine room auxiliaries – All machinery in the engine room which assist in the working of the
propulsion plant: coolers, heaters, pumps, separators, etc.
COMPRESSED AIR SYSTEMS FOR VARIOUS SHIPBOARD OPERATIONS
The main aim of a compressor, as the name suggests, is to compress air or any fluid in order to reduce its
volume. Some of the main applications of compressors onboard ships are main air compressor, deck air
compressor, AC compressor and refrigeration compressor. Failure to start or control air compressor can
be inconvenient, costly and can carry risks, which need to be managed.
Compressed air has many uses on board ship, ranging from diesel engine starting to the cleaning of
machinery during maintenance. Ships compressed air systems are usually divided into one or more of the
following:
• Main and auxiliary engine starting air system (high pressure).
• Service air.
• Control air.
• Instrument air.
• Deck services
Low pressure (5-8 bar) air may be supplied by either individual compressors or pressure reducing valves
fitted within the high-pressure circuit.
High Pressure System
The Main and Auxiliary Engine starting air supply is to be monitored carefully for excess oil and water.
Where compressors are fitted with cylinder lubrication then particular attention to the cylinder oil feed is
required. Moisture traps and drain valves are to be blown down at regular intervals. Should the blowdown
indicate excessive oil or moisture then the reason is to be immediately investigated.
All operating valves in the starting air system are to be operated slowly and with extreme caution. Do not
stand directly in front of a high-pressure valve when opening or closing. The Engine Room Staff are to be
made fully aware by the Chief Engineer of the importance of correct operation and maintenance of the
starting air compressors, and the effects of their failure during manoeuvring of the vessel. During
manoeuvring of the main engine, the starting air compressors are to be monitored locally for any sign of
overheating or problem.
Low Pressure System
Compressed air equipment which supplies low pressure air for control or instrument purposes must be
monitored constantly for moisture or other contaminants. Air, which is wet or contaminated, will have
detrimental effects upon engine manoeuvring systems and process control.
All filters and moisture traps are to be cleaned and serviced as per the maker’s instructions or at intervals
determined by operational experience. Short cycling of compressors indicated excessive consumption
(leakage) must be investigated immediately. Long periods of compressor running are also to be
investigated.
,Dryers
For engine room service, refrigerant tap driers are normal practice. These units give long service with
little maintenance; however, manufacturer’s instructions must be adhered to. In some cases, absorption
type driers are fitted which require strict change over routines.
Deck Service Compressors
Unwarranted use of these machines is to be avoided at all times. It is essential that any deck services are
shut down when not required. Supply from the main starting compressors via reducing valves is not to be
used for deck general service air supply unless an emergency exists.
Alarms
All compressor alarms, shut downs and measuring instruments are to be checked and calibrated at regular
intervals and in line with the Planned Maintenance requirements. Emergency Air Compressors are to be
tested as part of the weekly safety routines onboard.
Safety precautions
A recent case involving the failure of a control air compressor on board a ship illustrates how essential the
control air system is to safe operations. The compressor in question provided compressed air to the main
engine clutches. Failure of the air supply resulted in failure of the clutches. The ship sustained collision
damage and subsequent delays.
The control air receiver was insufficiently topped up to re-engage the clutches. It is recommended that
when one air compressor fails, the air receivers should be kept topped up at all times by the standby
compressor.
Repair of the air compressor should be prompt. The engine room should operate a watch system and the
Unattended Machinery Space notation should be considered suspended.
It is also recommended that the low air pressure alarm and set point be checked on a regular basis using
currently calibrated gauges.
Usually a two-stage, two-crank air compressor machine used aboard ship to supply compressed air. The
air is compressed in the first stage, cooled and compressed to higher pressure in the next stage.
Compressors must always be started at the unloaded condition since otherwise pressures build up rapidly
producing very high starting torques.
Compressed air has many uses on board ship, ranging from diesel engine starting to the cleaning of
machinery during maintenance. The air pressures of 25 bar or more are usually provided in multi-stage
machines. Here the air is compressed in the first stage, cooled and compressed to a higher pressure in the
next stage, and so on. The two-stage crank machine is probably the most common.
Air is drawn in on the suction stroke through the first-stage suction valve via the silencer/filter. The
suction valve closes on the piston upstroke and the air is compressed. The compressed air, having reached
its first-stage pressure, passes through the delivery valve to the first-stage cooler. The second-stage
suction and compression now take place in a similar manner, achieving a much higher pressure in the
smaller, second-stage cylinder.
After passing through the second-stage delivery valve, the air is again cooled and delivered to the storage
system. The machine has a rigid crankcase which provides support for the three crankshaft bearings. The
cylinder block is located above and replaceable liners are fitted in the cylinder block. The running gear
consists of pistons, connecting rods and the one-piece, two-throw crankshaft.
, Fig: Two stage air compressor
The first-stage cylinder head is located on the cylinder block and the second-stage cylinder head is
mounted on the first: each of the heads carries its suction and delivery valves. A chain-driven rotary-gear
pump provides lubricating oil to the main bearings and through internally drilled passages in the
crankshaft to both connecting rod bearings. Cooling water is supplied either from an integral pump or the
machinery space system. The water passes into the cylinder block which contains both stage coolers and
then into the first and second stage cylinder heads.
A water jacket safety valve prevents a build-up of pressure should a cooler tube burst and compressed air
escape. Relief valves are fitted to the first and second-stage air outlets and are designed to lift at 10%
excess pressure. A fusible plug is fitted after the second-stage cooler to limit delivered air temperature
and thus protect the compressed-air reservoirs and pipework.
Cooler drain valves are fitted to compressors. When these are open the machine is 'unloaded' and does not
produce compressed air. A compressor when started must always be in the unloaded condition. This
reduces the starting torque for the machine and clears out any accumulated moisture in the system. This
moisture can affect lubrication and may produce oil/water emulsions which line the air pipelines and
could lead to fires or explosions.
The compressor motor is started and the machine run up to speed. The lubricating oil pressure should be
observed to build up to the correct value. The first-stage drains and then the second-stage drains are
closed and the machine will begin to operate. The pressure gauge cocks should be adjusted to give a
steady reading. Where manual drains are fitted they should be slightly opened to discharge any moisture
which may collect in the coolers. The cooling water supply should be checked, and also operating
temperatures, after a period of running loaded.
To stop the compressor, the first and second-stage cooler drain valves should be opened and the machine
A term applied collectively to all machinery and apparatus forming the non propulsive equipment of a
ship.
- Deck auxiliaries, deck equipment, deck machinery – All machinery used for working the vessel and
handling the cargo: winches, windlass, steering gear, cranes, etc.
- Engine room auxiliaries – All machinery in the engine room which assist in the working of the
propulsion plant: coolers, heaters, pumps, separators, etc.
COMPRESSED AIR SYSTEMS FOR VARIOUS SHIPBOARD OPERATIONS
The main aim of a compressor, as the name suggests, is to compress air or any fluid in order to reduce its
volume. Some of the main applications of compressors onboard ships are main air compressor, deck air
compressor, AC compressor and refrigeration compressor. Failure to start or control air compressor can
be inconvenient, costly and can carry risks, which need to be managed.
Compressed air has many uses on board ship, ranging from diesel engine starting to the cleaning of
machinery during maintenance. Ships compressed air systems are usually divided into one or more of the
following:
• Main and auxiliary engine starting air system (high pressure).
• Service air.
• Control air.
• Instrument air.
• Deck services
Low pressure (5-8 bar) air may be supplied by either individual compressors or pressure reducing valves
fitted within the high-pressure circuit.
High Pressure System
The Main and Auxiliary Engine starting air supply is to be monitored carefully for excess oil and water.
Where compressors are fitted with cylinder lubrication then particular attention to the cylinder oil feed is
required. Moisture traps and drain valves are to be blown down at regular intervals. Should the blowdown
indicate excessive oil or moisture then the reason is to be immediately investigated.
All operating valves in the starting air system are to be operated slowly and with extreme caution. Do not
stand directly in front of a high-pressure valve when opening or closing. The Engine Room Staff are to be
made fully aware by the Chief Engineer of the importance of correct operation and maintenance of the
starting air compressors, and the effects of their failure during manoeuvring of the vessel. During
manoeuvring of the main engine, the starting air compressors are to be monitored locally for any sign of
overheating or problem.
Low Pressure System
Compressed air equipment which supplies low pressure air for control or instrument purposes must be
monitored constantly for moisture or other contaminants. Air, which is wet or contaminated, will have
detrimental effects upon engine manoeuvring systems and process control.
All filters and moisture traps are to be cleaned and serviced as per the maker’s instructions or at intervals
determined by operational experience. Short cycling of compressors indicated excessive consumption
(leakage) must be investigated immediately. Long periods of compressor running are also to be
investigated.
,Dryers
For engine room service, refrigerant tap driers are normal practice. These units give long service with
little maintenance; however, manufacturer’s instructions must be adhered to. In some cases, absorption
type driers are fitted which require strict change over routines.
Deck Service Compressors
Unwarranted use of these machines is to be avoided at all times. It is essential that any deck services are
shut down when not required. Supply from the main starting compressors via reducing valves is not to be
used for deck general service air supply unless an emergency exists.
Alarms
All compressor alarms, shut downs and measuring instruments are to be checked and calibrated at regular
intervals and in line with the Planned Maintenance requirements. Emergency Air Compressors are to be
tested as part of the weekly safety routines onboard.
Safety precautions
A recent case involving the failure of a control air compressor on board a ship illustrates how essential the
control air system is to safe operations. The compressor in question provided compressed air to the main
engine clutches. Failure of the air supply resulted in failure of the clutches. The ship sustained collision
damage and subsequent delays.
The control air receiver was insufficiently topped up to re-engage the clutches. It is recommended that
when one air compressor fails, the air receivers should be kept topped up at all times by the standby
compressor.
Repair of the air compressor should be prompt. The engine room should operate a watch system and the
Unattended Machinery Space notation should be considered suspended.
It is also recommended that the low air pressure alarm and set point be checked on a regular basis using
currently calibrated gauges.
Usually a two-stage, two-crank air compressor machine used aboard ship to supply compressed air. The
air is compressed in the first stage, cooled and compressed to higher pressure in the next stage.
Compressors must always be started at the unloaded condition since otherwise pressures build up rapidly
producing very high starting torques.
Compressed air has many uses on board ship, ranging from diesel engine starting to the cleaning of
machinery during maintenance. The air pressures of 25 bar or more are usually provided in multi-stage
machines. Here the air is compressed in the first stage, cooled and compressed to a higher pressure in the
next stage, and so on. The two-stage crank machine is probably the most common.
Air is drawn in on the suction stroke through the first-stage suction valve via the silencer/filter. The
suction valve closes on the piston upstroke and the air is compressed. The compressed air, having reached
its first-stage pressure, passes through the delivery valve to the first-stage cooler. The second-stage
suction and compression now take place in a similar manner, achieving a much higher pressure in the
smaller, second-stage cylinder.
After passing through the second-stage delivery valve, the air is again cooled and delivered to the storage
system. The machine has a rigid crankcase which provides support for the three crankshaft bearings. The
cylinder block is located above and replaceable liners are fitted in the cylinder block. The running gear
consists of pistons, connecting rods and the one-piece, two-throw crankshaft.
, Fig: Two stage air compressor
The first-stage cylinder head is located on the cylinder block and the second-stage cylinder head is
mounted on the first: each of the heads carries its suction and delivery valves. A chain-driven rotary-gear
pump provides lubricating oil to the main bearings and through internally drilled passages in the
crankshaft to both connecting rod bearings. Cooling water is supplied either from an integral pump or the
machinery space system. The water passes into the cylinder block which contains both stage coolers and
then into the first and second stage cylinder heads.
A water jacket safety valve prevents a build-up of pressure should a cooler tube burst and compressed air
escape. Relief valves are fitted to the first and second-stage air outlets and are designed to lift at 10%
excess pressure. A fusible plug is fitted after the second-stage cooler to limit delivered air temperature
and thus protect the compressed-air reservoirs and pipework.
Cooler drain valves are fitted to compressors. When these are open the machine is 'unloaded' and does not
produce compressed air. A compressor when started must always be in the unloaded condition. This
reduces the starting torque for the machine and clears out any accumulated moisture in the system. This
moisture can affect lubrication and may produce oil/water emulsions which line the air pipelines and
could lead to fires or explosions.
The compressor motor is started and the machine run up to speed. The lubricating oil pressure should be
observed to build up to the correct value. The first-stage drains and then the second-stage drains are
closed and the machine will begin to operate. The pressure gauge cocks should be adjusted to give a
steady reading. Where manual drains are fitted they should be slightly opened to discharge any moisture
which may collect in the coolers. The cooling water supply should be checked, and also operating
temperatures, after a period of running loaded.
To stop the compressor, the first and second-stage cooler drain valves should be opened and the machine
