The air compressors on ship are important equipment that provides the initial power for the ship from static to navigation operation. The output power of modern large-scale ship diesel engines is increasing day by day, and the cylinder diameter and journal size of diesel engines are getting larger and larger. Ship air compressors have become an indispensable device that affects the safe navigation of ships.

What is air compressor on ship?

Air compressors on ship compress normal temperature and pressure air into high-temperature and high-pressure compressed air through single-stage or multi-stage compression, and provide it to the starting air system, pneumatic control system and other equipment of the ship’s main engine and auxiliary engine to help the ship’s engine work.

However, as the size of the ship increases, the demand for compressed air will also increase, and the start and stop of the ship air compressor will become more frequent.

Ship air compressors also provide compressed air for many pneumatic equipment such as hydraulic jacks, heat exchangers, boilers and cleaning tools on ship, as the power source of these applications. The normal operation of the air compressor will directly affect the safe and reliable navigation of the ship.

Ship air compressors working principle

Ship air compressors include reciprocating air compressors, screw compressors, centrifugal compressors, scroll compressors, and other types.

Take the reciprocating compressor as an example: the reciprocating piston air compressor on ships is driven by the motor to rotate the shaft, and then the connecting rod drives the piston to produce reciprocating motion, so that the volume of the piston chamber composed of the air valve, piston and cylinder changes, and the purpose of compressing air is achieved. When the pressure ratio is relatively large, multi-stage compression is used.

(KT Series 20 – 40 Bar Middle Pressure PET Piston Air Compressor)

Considering the rated power and volume of the marine air compressor and other factors, two-stage compression is generally selected. The atmosphere is compressed in the low-pressure cylinder, and then passes through the inter-cooler to release heat to the cooling water under isobaric pressure, and then enters the high-pressure cylinder. The gas is further compressed to the required pressure and stored in the air tank.

The air compressor with two-stage compression can improve the gas transmission coefficient and reduce the force on the piston. At the same time, an inter-cooler is set between the high-pressure cylinder and the low-pressure cylinder.

The gas compressed in the low-pressure cylinder is cooled to room temperature by the inter-cooler and then enters the high-pressure cylinder for compression. The temperature at the compression end is almost the same as that at the low-pressure cylinder, thus ensuring good lubrication conditions for the cylinder, saving compression work, and improving efficiency. The temperature at the compression end is relatively lower.

There is another type of compressor on ship, breathing air compressors are specially designed high-pressure air compressors for diving and marine works, which is also known as scuba compressor. It can develop high pressure and clean breathing air to help people to breath easier in deep water environment where fluid pressure can be very high.

(KBC Series Air Compressor)

Air compressors on ship troubleshooting

In consideration of the importance of ship air compressors, there will usually be two air compressors on board, one for normal use and one for standby. These air compressors need to withstand humid environments, as well as the salt present in water and air.

Not all metals can withstand these conditions, so using marine air compressors that are not designed for these specific conditions may cause equipment failures or even safety hazards.

As the operating time of the air compressors on ship increase, any abnormality may be a sign of failure. Fault phenomena have certain characteristics, such as visible, audible, and tactile, which can be summarized as follows:

Startup problem: such as the air compressor is not working, sudden shutdown, severe vibrations, or the motor rotation speed is unstable during operation, etc.

Performance problem: such as reduced exhaust volume, low exhaust pressure, slow pressure rise rate, etc.

Abnormal sound : such as various abnormal knocking sounds, friction sounds, air leakage sounds, etc.

Abnormal temperature: such as oil and water temperature indications are too high or too low, the surface temperature of parts and compressed gas temperature are too high, etc.

Abnormal appearance: such as an excess of oil and water droplets mixed in the compressed air, too much humidity, too high dew point, and other phenomena.

In addition to the above faults, ship air compressors may also have some problems that are difficult to judge and solve.

In order to ensure that the air compressor can operate smoothly and reliably for a long time and extend the service life of the unit, it is necessary to strictly follow the equipment operating procedures, formulate a detailed maintenance plan, conduct regular inspections and maintenance, keep the equipment clean, remove oil and water from compressed air, and reduce the intrusion of dust and debris into the oil cooler and cooling pipes.