Chapter 4 N38143 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. Air expands more than coolant when heated and may cause loss of coolant from the engine system through the expansion tank overflow. 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. 2. 3.
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 o C at both 1500 and 1800 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 3 /s for the Na/ turbo and 2.5m 3 /s for the aftercooled engines at 1800 rpm.
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. Page 26