Air Compressor Onboard the Ship Working and Operation

Image of two stage air compressor
Image credits: Brian S. Elliott license under  Creative Commons Attribution-Share Alike 4.0 International

Air compressor onboard the ship will help for many applications. Such as starting the main engine and also using to clean some machinery at the time of maintenance. The pressure of compressed air is about 25 bar usually in the case of multistage machinery. But the pressure of the air for starting the marine diesel engine is about 30 bar. The operation of compressing the air is like, at the first stage the air will get compressed and then the air will get cooled. And in the next step, the air will again be compressed at high pressure. The most common type is the two-stage crank type.

Air Compressor Onboard the Ship Working:

Air compressor onboard the ship working is like, at the first stage the air will be drawn to the chamber at the suction stroke through the suction valve by passing through the filter. And then the piston of the compressor will go upward and then the air gets compressed. And at this time the air will achieve the maximum compression at high pressure. After this, the sir will passes to the first stage cooler through the delivery valve between it. Then with the same manner, next the second stage compression ill take place by taking suction from the first stage of the compression.

Through this, the air will achieve much high-pressure compression by the second stage smaller cylinder. The first stage compressor cylinder is larger while the second stage compression cylinder is smaller. And after the second stage compression, the compressed air will passes to the cooler through a delivery valve. And next to the storage system.

Air Compressor Onboard the Ship Construction:

Air compressor onboard the ship working and construction is, the crankcase that presents in the system is very strong enough to withstand the high pressure. Also, this crankcase will give support to the bearings of the crankshaft. There will be some replaceable liners in the cylinder block. Also, the cylinder block will be in the upper part. Then the running gear has the piston, connecting rods and the crankshaft. The cylinder head of the first stage compressor will be on the cylinder block meanwhile the cylinder head of the second stage compressor will be on the head of the first stage compressor.

Also, both cylinder heads have their own suction valve and delivery valve. The lubrication to the main bearing is done by the chain driving rotary gear pump. Also, the lubrication for the crankshaft and the connecting rod is through the internal drilled passage. The cooling water will get from the pump or will also get from the machinery space system. The cooling water initially goes to the cylinder block that has stage coolers. After that, it will pass to the first stage cylinder head and then to the second stage cylinder head.

Also, there will be a safety valve for jacket water. This will help to prevent the pressure build-up which will later affect the compressor system. And there will be a relief valve on the first stage air outlet and on the second stage air outlet. Also, after the second stage cooler, there will be a fusible plug on it. This will use to regulate the temperature and protect the compressor system and also the air reservoir. Also, the cooler drain valve will use to unload the system and thus to stop compression. This will happen when only the drain is in an open condition.

Related Articles: Marine heat exchangers: Working and Operations.

Air Compressor Onboard the Ship Precautions:

Air compressor onboard the ship working and precautions include, the compressor will start and then come to speed. Then we should check the lubrication oil pressure for the correct value. When the system starts to operate, then the drain in the first stage and the drain in the second stage should close. Also, check the pressure gauge cocks to get the steady readings. If there is any manual drain will fit, then it should discharge frequently to remove the moisture that presents in the cooler. Also, we should concern about the cooling water supply, operating temperature after the system achieve some speed.

And in the case of stopping the compressor, we should not forget to open the first stage and the second stage cooler drains. also, before stopping the compressor, the system should run in unload condition for about three minutes. After these steps, now we can stop the compressor system and the drains should remain open. Also, take care to isolate the cooling water if the system is stopping for a long time.

In the case of automatic compression operations, it needs some additional equipment to work. An unloader is there in the system. This is to ensure that the system will start at the unload condition. The most common type to achieve the unload condition is the depressors. This will help to hold the suction valve to remain in their seats. Also, there will be automatic drains that will help to remove the moisture content. And the usual equipment relief valve is there to avoid the backflow. Also, a special kind of oil-free compressor will use for supplying the control air. To remove the moisture and the impurities, this air will passe to the filter.


To maintain the system, there will be some checks that we should do frequently such as crankcase oil level, cooling water system, parameters like pressure and temperature. Also, there will be some frequent need of repairing some equipment. Checks the suction air valves and the delivery air valves at each stage. The fast and frequent opening and closing of the valve will cause damage. So we should take care to check the seats of the valves frequently.

The use of bad lubrication oil and the presence of such dirt will cause overheat to the system. All valves in the system should check regularly and also the parts should examine and clean perfectly. If you find any damage or worn parts, it should replace at the moment. So all the spare equipment should available on the ship.

Note: The article and the pictures should not be copied or reproduced without the permission of Marinewheel.

Conclusion: Here is the full details of the Air compressor working, operations and maintenance. Hope you got the idea about this. Comment your queries and opinions below.


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