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| Illustration 1 | g01040648 |
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(1) Recovery Bottle with a vented cap
(2) Expansion Tank with a pressure relief cap | |
A pressure type cooling system offers two advantages:
- The cooling system can operate safely at a temperature that is higher than the normal boiling point of water.
- The cooling system prevents cavitation in the water pump.
Cavitation is the sudden formation of low-pressure bubbles by mechanical forces in liquids. The formation of air or steam pockets is more difficult within a pressure type cooling system.
The shunt line prevents cavitation by the water pump. The shunt line provides additional flow of coolant to the water pump inlet.
The recovery bottle (1) provides space for expansion of the coolant volume while the engine is running. Also, the recovery bottle provides space for expansion during the warm-up cycle. The recovery bottle also provides a means for checking the coolant level.
In many instances, a separate cooling source is used to supply coolant to the aftercooler. The coolant supply can be fresh water, or the coolant supply can be sea water. Because of the possible unknown composition of the cooling water, a special pump is needed to move the coolant through the system. Two types of pumps are available for use in the raw water circuit.
- A bronze pump is used when sea water enters the system. This type of pump will resist the corrosive action of the coolant that passes through the pump.
- A cast iron pump is used when the coolant is pure and noncorrosive.
Raw water is drawn in through the inlet of the auxiliary water pump. The raw water will flow through the fuel cooler before the auxiliary water pump inlet if the engine is equipped with the optional fuel cooler. The raw water is forced out of the pump and into the aftercooler. The raw water flows through the aftercooler and exits at the end of the aftercooler. The raw water then travels through the marine gear cooler(if equipped), the heat exchanger, and the exhaust elbow (if equipped). The raw water is then discharged.
The water pump is located on the side of the cylinder block. The water pump is gear-driven from the crankshaft.
Coolant from the heat exchanger is pulled into the inlet of the water pump by impeller rotation. The coolant exits the pump directly into the engine oil cooler.
After the water exits the oil cooler, the water is dispersed to three main components: cylinder block and head, turbocharger and exhaust manifold.
The coolant that was directed to the cylinder block next flows into the cylinder head.
The coolant exits the cylinder head and combines with the flow of coolant from the exhaust manifold and the turbocharger. The combined coolant then flows to the water temperature regulator. The coolant then flows through a deaerator in order to purge excess air to the expansion tank. The water is then returned to the heat exchanger in order to be cooled.
The coolant recovery bottle adds volume for expansion of the coolant in the engine cooling system. The coolant recovery bottle also provides a convenient way to check the coolant level. Coolant is forced into the bottle during the warm-up cycle. Coolant returns to the heat exchanger from the recovery bottle during the cool down cycle.
Air vents are provided on the water outlet of the turbocharger. The air vents aid in removing air from the system during the initial filling of the cooling system. The air vents also aid in removing air from the system after a flushing process.
Note: The water temperature regulator controls the direction of flow. When the coolant temperature is below the normal operating temperature, the water temperature regulator is closed. The coolant is directed from the cylinder head to the inlet of the water pump. When the coolant temperature reaches the normal operating temperature, the water temperature regulator opens. Coolant then travels to the heat exchanger for cooling.
Note: The water temperature regulator is an important part of the cooling system. The water temperature regulator divides coolant flow between the heat exchanger and the bypass in order to maintain the normal operating temperature. If the water temperature regulator is not installed in the system, there is no mechanical control, and most of the coolant will travel the path of least resistance through the bypass. This action will cause the engine to overheat in hot weather and the engine will not reach normal operating temperature in cold weather.
There are two types of systems for heat dissipation that are recommended for use with Caterpillar marine engines. These systems for heat dissipation involve the use of either inboard mounted heat exchangers or outboard mounted keel coolers.
Inboard mounted heat exchangers are typically designed as a shell that surrounds many thin tubes. Systems that are cooled with a heat exchanger require a sea water pump in order to circulate sea water through the thin tubes in the heat exchanger. Cooling system water is then circulated in the opposite direction through the shell that surrounds the tubes. Heat is transferred from the hot coolant to the cool sea water that is flowing through the thin tubes.
One alternative method of removing heat from coolant circuits on marine engines is by using a keel cooler (if equipped). A keel cooler is an outboard heat exchanger which is attached to the submerged part of the hull of a ship. The keel cooler is typically long sections of pipe. The pipes are attached to the hull of the boat near the keel. Coolant is circulated through the piping by the water pump that is driven by the engine. The keel cooler transfers heat from the coolant into the surrounding sea water. Two important factors that determine the effectiveness of the keel cooler are the operating speed of the vessel and the surrounding water temperature. This system is a closed system. Sea water does not enter any portion of the system.