High temperature circuit cooling system

In ships, the high-temperature cooling circuit is mainly used to cool internal combustion engines and more powerful (usually second-stage) gas compressors. As the variety of these possible systems and the limited scope of the topic do not allow us to discuss all possible options, the principles of operation of a high-temperature cooling system will be illustrated by the example of the main engine cooling.
The closed-loop, high-temperature (HT) cooling water system of the main engine has two circulators with electric drive (otherwise one pump can be driven from the crankshaft or various combinations of several different gear types). The system supplies cooling water for cooling the main engine cylinders, their heads, exhaust valves and turbocharger.
Circulation pumps supply cooling water to the main engine intake manifold and direct part of it to the water heater or fresh water generator. Water from the cooling system is continuously drained from the top of the cooling unit to the fresh water expansion tank, which is shared by the high temperature cooling circuit system with the low temperature cooling circuit system (other cooling systems may have separate expansion tanks).
The three-way valve controlled by the HT cooling water circuit thermostat is in the return line to the circulating water pumps. This valve ensures the connection of the high-temperature and low-temperature circuits of the central cooling system. In operation, this valve directs the required amount of water from the high-temperature cooling system side to the low-temperature cooling side (another way of cooling the water in the HT cooling circuit is possible - using heat exchangers). In this way, the correct operating temperature of the unit is maintained by the cooling water leaving the engine.
Additional water is supplied from the low temperature (LT) system circuit to the HT cooling circuit system via a dedicated valve (Figure 9), which is opened each time the main engine is running or may be running.
In order to reduce the ingress of air into the central freshwater cooling system, the circulating water is returned to the suction piping of the high-temperature cooling water pumps through a deaerator from which air or gas is removed to the freshwater expansion tank.
A freshwater expansion tank that is common to both circuits of the central freshwater cooling system (high and low temperatures) is designed to provide the required static pressure in the freshwater cooling systems. This tank also allows for the thermal expansion of the cooling water due to the different water temperatures when the engine is switched off and running at full load. If the level in the tank rises too much, it is poured into the dirty bilge water tank through the installed overflow line.

Example of a high temperature circuit cooling system for a main engine