Operational procedure of main air compressor or Checks to be done on main air compressor during start, stop and operation

The compressor you see is a two cylinder , two stage, double acting, water cooled compressor.

The air is inducted into compressor through the air filter. the compressed air is cooled by an inter-cooler and after cooler.
Oil water separators are provided to separate the oil and moisture from the compressed air.
Low pressure and high pressure stage drains are connected to an automatic unloader, which unloads the compressor while starting and stopping.
The compressed air delivered to an air reservoir for storage.

Before you start the compressor you have to carry out a few checks -

  • Lube oil level: Check if the oil level in the sump is normal through the level gauge. if the level is high oil will carry over. a low level of oil will result in improper lubrication.
  • Delivery side valves: Check if air bottle filling valve and the compressor delivery valve are open. If you start the air compressor with the delivery side valves shut, the relief valve will lift. be careful, the compressor may explode if the relief valve malfunctions.
  • Drain valves: Make sure that the low pressure and high pressure stage drain valves are open. the drains are connected to the unloader. starting the compressor with the drain valves shut will overload the compressor.
  • Cooling water system valves: Ensure that all the seawater and fresh water system are open. the cooling water temperature and the air temperature will increase, if the cooling water flow is restricted.
  • Load on generators: Confirm that the generators can take of the compressor. this compressor motor consumes 30 kilo watts while running. the starting current will be higher.

Checks during starting of compressor :

  • Starting of air compressor : Start the compressor now. confirm that the automatic unloader has closed the drain, you can hear the sound of air draining stop. In addition, confirm that the compressor is loaded.
  • Compressor motor current : Check the current drawn by the compressor motor in the ammeter. If it is the higher than normal, it indicates that the compressor is overloaded.

During operation checks :

  • Lube oil pressure : Check if the lube oil pressure is normal around 2.8 bar. low lube oil pressure will lead to improper lubrication.
  • Cooling water temperature and pressure : Monitor the cooling water temperature and pressure. the cooling water pressure should be around 3.0 bar. Maintain the cooling water inlet temperature between 30 to 40 degrees centigrade. The cooling water pressure and temperature will affect the air temperature.
  • Delivery of air temperature : Monitor the delivery air temperature will affect the cylinder lubrication and reduce the efficiency of the compressor.
  • LP and HP delivery air pressure : Check the first and second stage delivery air pressure. observe the time taken for filling the air reservoir.
  • Air reservoir pressure : The time taken for pressure to rise in the air reservoir will indicate the performance of the compressor.
  • Abnormal noise or vibration : Checks for any abnormal noise or vibration. stop the compressor immediately if you hear any abnormal noise. do not start the compressor without investigating the reasons for abnormality.
  • Checks during the stopping of compressor : When you stop the compressor, check whether the unloader opens to drain the air. In compressor where an unloader is not fitted, you should open the drains before stopping. And stop the compressor.


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