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Flexible Impeller Pumps - 14649 8

It is important that Jabsco engine cooling pumps and systems are matched during the design of ship’s engineinstallations. Once installed, safety margins must be safeguarded, i.e. the emphasis must be on PREVENTIVE, not corrective maintenance.Cooling systems most commonly used for marine propulsion engines are:

â–  Heat exchanger cooling â–  Keel cooling â–  Direct cooling

Heat Exchanger Cooling

Engine CoolingIntroduction This is also known as a closed system The heat exchange r, which can be single-pass or two-pass type, should be capable of handling approximately 10% more thanthe maximum engine heat rejection rate and may be fitted separately or as an integral part of the expansion/header tank. Thistank allows venting of air or combustion gases absorbed by the cooling water during engine operation and provides a positive pressure on the fresh water pump inlet. This pump, fitted in the coldest part of the primary circuit, has a capacity which will maintain a water temperature differential of approximately 45°F (8ËšC) across the cylinder block at full load. The engine operatingtemperature is regulated by a marine thermostat to about 185°F (85ËšC) on most engines. To provide an adequate safety margin for commercial diesel engines, which may be expected to operate more than 2500-3000 hours per year, size and rpm of the Jabsco raw water pump should be selected to give a flow capacity of approximately 15 GPM for every 100 HP maximum engine load and rpm.If an exhaust manifold is fitted in the raw water or fresh water circuit, the raw water pump flow capacity should be 10-15% higher. , i.e. the primarycooling circuit is isolated from the surrounding atmosphere.A centrifugal pump circulates fresh, treated water through the cylinder block passages and around the tube stack of a heat exchanger. The Jabsco raw water pump draws raw water (from sea or lake) through the ship’s hull inlet and pumps it through the heat exchanger tubes where it removes the heat transmitted from the primary circuit before discharging overboard. Additional coolers , such as oil coolers, charge air coolers, must be fitted AFTER the pump but in a compromise betweenreliability, size and weight, and pump delivery. Head should be about 10–13 psi of water at maximum rpm. Safety margins in pump inlet systems, are extremely critical so any restrictions or bends, other than seacock and inletstrainers, are to be avoided at all costs (see also Suction Systems).Raw water from the exhaust manifold is often injected into the exhaust pipe (AFTER an exhaust elbow to prevent raw waterflowback into the cylinders) which may then be ducted through areas where a hot pipe would create a hazard. This is known as a WET EXHAUST system. In addition, mixing of water with exhaust gases will reduce exhaust noise. However, on small engines the raw water flow should not be less than 2
1 / 2 -4 GPM for adequate silencing.
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