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Chapter 4
Keel coolers should be installed below the waterline far enough to avoid the aerated water close to the sur-
face. Recessed and shielded coolers must allow for unobstructed flow around the coolers. The keel coolers
should be installed so that air pockets are not present during the initial fill. Vents at all high points along the
connecting pipes will be necessary.
Keel coolers should not be fitted where they would be exposed to pounding seas or hull flexing. The bow
of the vessel is not considered to be a good location whereas adjacent to the keel, where it is the strongest
area of the vessel, is the preferred location.
De-aeration
Warning! Air in the engine coolant can cause the following problems:
1.
Air accelerates the corrosion within the engine water passages that can lead to high water temperatures
as silt deposits on the surface of the cooler reducing the heat transfer. Premature failure of the engine can
occur.
2.
Air expands more than coolant when heated and may cause loss of coolant from the engine system through
the expansion tank overflow.
3.
In an extreme case, air will collect in one area and cause a loss of coolant flow around the cylinder block
resulting in piston seizure and major engine damage.
Radiator cooled
Radiator cooled engines are typically used for emergency units or if the engine is located more than 4m
above the sea water, such as on the deck of barges.
The radiator cores are fully tinned to give the best corrosion protection and are therefore capable of operat-
ing in worldwide environments. The design allows for air on temperatures of 50
rev/min, 50% ethylene glycol and 200Pa duct allowance. The air velocity over the radiator is 5m/s for both
the NA/turbo and turbo aftercooled engines. A pusher fan is used that has an airflow of 1.8m
turbo and 2.5m
/s for the aftercooled engines at 1800 rpm.
3
Expansion Tank
The expansion volume in the tank must be large enough for the entire cooling system. Since the engine cool-
ant expands about 5% between cold and hot engine operating temperatures, the expansion tank must have
a volume equal to 5% of the entire cooling system volume.
When designing the larger expansion tank the following allowance should be made:
•
A 50 kPa pressure cap should be fitted to pressurise the system.
•
3% to 5% of total system capacity for expansion losses
•
10% of total system capacity for volume loss on hot shut down
•
5% of total system capacity for working volume
The illustration (I) shows the allowances required when designing a larger expansion tank.
Engine bleed (Vents)
Warning! Joining the bleed pipes into a common vent will reduce the total water flow and may result in aerated
water flowing back into the engine resulting in the engine overheating and possible failure.
The engine bleed system provides a continuous flow of water through the expansion tank as a method of
removing air from the engine coolant. Depending on the model of the engine there can be up to three bleed
pipes which need to be connected to the top of the expansion tank. Each bleed must be connected to the
expansion tank without using tee's or other fittings that would join the bleed pipes together in a common
vent.
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C at both 1500 and 1800
o
/s for the Na/
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