Jacket Water Cooling System of Main Engine Marine Diesel Engine

 Below Fig shows a typical jacket water system for marine diesel engines.

Header Tank/ Expansion Tank:  

    Expansion tank having mainly three functions storage fresh water, Maintain constant head and allow for the expansion/contraction of the water as its temperature changes. It is also known as a Make up water tank.

Air Separator/ De-Aerator: 

 It is an important component in the system, de aerator removes the air accumulated in the system. Air is accumulated in the system because of the heating of water or improper purging after maintenance. If its not removed air lock in the system likely to happen

J.W Cooler

Cooling can be done by dedicated coolers which cools the hot jacket water from the main engine. Cooling medium is fresh water or sea water, in new ships central cooling systems are used, where fresh water as a cooling medium. 

Circulating Pump:

 There are two jacket water circulating pumps used onboard with a discharge pressure of 3-4 bars. The Circulating Pump takes suction from the deaeration tank to the main engine.


When the main engine is not running or the ship is passing through colder areas it is necessary to keep the jacket water temperature at 80-85 degree Celsius. To do this job a Pre heater is provided, which will not allow the jacket water temperature below 80-85 degree Celsius.

Fresh Water Generator: Fresh water generators act as a cooling component in the jacket water system. It uses the waste heat for producing distilled water.

Valve controller

      Which will control the three way valve according to the jacket water engine outlet temperature. If the temperature at outlet is less than the desired value valve controller bypass the cooler with the help of 3 way valve

You can answer following question

> Explain Jacket water system of main engine

> Why Freshwater generator incorporated with jacket water system?

> Use of De-aerator in jacket water system 


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