Page 45 - Introduction to Marine Engineering

32 Diesel engines

other Individual coolers. With less equipment in contact with sea water
the corrosion problems are much reduced in this system.
A sea water cooling system is shown in Figure 2.19. From the sea
suction one of a pair of sea-water circulating pumps provides sea water
which circulates the lubricating oil cooler, the jacket water cooler and the
piston water cooler before discharging overboard. Another branch of
the sea water main provides sea water to directly cool the charge air (for
a direct-drive two-stroke diesel).
One arrangement of a central cooling system is shown in Figure 2.20.
The sea water circuit is made up of high and low suctions, usually on
either side of the machinery space, suction strainers and several sea
water pumps. The sea water is circulated through the central coolers and
then discharged overboard. A low-temperature and high-temperature
circuit exist in the fresh water system. The fresh water in the
high-temperature circuit circulates the main engine and may, if
required, be used as a heating medium for an evaporator. The
low-temperature circuit circulates the main engine air coolers, the
lubricating oil coolers and all other heat exchangers. A regulating valve
controls the mixing of water between the high-temperature and
low-temperature circuits. A temperature sensor provides a signal to the

-HI

Jacket
water
cooler

Piston
water Lubricating
cooler oil cooler

Pumps
Sea water
suction

Figure 2.19 Sea water cooling system