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COOLING SYSTEM (EXTERNAL)
1.
DESCRIPTION
Westerbeke
marine
diesel
engines
are
equipped
with
fresh
water
cooling.
Transfer of heat from engine fresh water to sea water
is
accomplished by a heat exchanger, similar in function to an automotive
radiator.
Sea water
flows through the tubes of the heat exchanger
while fresh water flows around the tubes.
The sea water and fresh
water never mix with the result that the cooling water passages in the
engine stay clean.
2.
FRESH WATER CIRCUIT
Heat rejected dur ing combustion, as well as heat developed by fr ic-
tion, is absorbed by the fresh water whose flow is created by a fresh
water circulating pump.
The fresh water flows from the engine through
a fresh water cooled exhaust manifold, a heat exchanger, in most cases
an oil cooler, and returns to the suction side of the fresh water cir-
culating pump.
The flow is not necessarily in this order in every
model.
When starting a cold engine, most of the external flow to the
heat exchanger is prevented by the closed thermostat.
Some amount of
by-pass is maintained to prevent overheating in the exhaust manifold.
As the engine warms up, the thermostat begins to open up allowing full
flow of engine fresh water through the external cooling system.
3.
SEA WATER CIRCUIT
The sea water
flow
is created by a posi ti ve displacement neoprene
impeller pump (gear pump in certain special cases).
Normally the pump
draws sea water directly from the ocean via the seacock and sea water
strainer.
Sometimes a transmission oil cooler, or perhaps a V-drive,
will be piped on the suction side of the sea water pump.
Generally,
it is better to have as few devices on the suction side of the sea
water pump as possible to preclude priming difficulties.
Usually sea
water flows directly from the discharge of the sea water pump to the
heat exchanger sea water inlet.
After passing through the tubes of
the heat exchanger, the sea water may enter a transmission oil cooler,
if present and if sea water cooled.
Ultimately, the sea water enters
a water injected, wet exhaust system, the most popular type of exhaust
system in use.
In the case of larger engines the sea water flow is
di vided pr ior
to enter ing the exhaust systems so that a portion is
used to cool the exhaust system.
Full sea water flow would create
unnecessary exhaust back pressure.
4.
SEA WATER PUMP
The sea water pump is self priming and positive displacement.
It is a
rotary pump with a non-ferrous housing and a neoprene impeller.
The
impeller
has
flexible vanes which wipe
against a curved cam plate
within the
impeller
housing,
producing
the pumping action.
On no
account should this pump be run dry.
There should always be a spare
impeller and impeller cover gasket aboard.
107
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