RAW
WATER
COOLING
CIRCUIT
DESCRIPTION
The
raw
water
cooling circuit is driven by a positive dis-
placement impeller pump. This pump draws
in
water directly
from an ocean, lake, or river, through the seacock, then to a
raw water strainer. The raw water is drawn through the
strainer to the self-priming pump and to the heat exchanger
where
it
cools the engine's circulating fresh water coolant.
The raw water is then discharged into the water injected
exhaust elbow mixing with and cooling the exhaust gases.
This mixture
of
exhaust gas and raw water is driven through
the exhaust system and overboard.
Transmission
oil
cooler.
In
some installations the raw water
is also used to cool the engine's transmission by passing
through a transmission oil cooler. Similar to a heat
exchanger, the transmission fluid is cooled by the raw water
and then passes into the exhaust elbow. The oil cooler should
be cleaned and pressure tested at about the same interval as
the heat exchanger, every
1000 hours.
TRANSMISSION
OIL
COOLERS
The
heat exchanger functions as part
of
the fresh water sys-
tem and the raw water system. The heat exchanger is a cop-
per tube which encloses a number
of
small copper tubes.
Raw water is pumped through the small copper tubes and
fresh water coolant from the engine is circulated around the
copper tubes. The raw water removes heat from the fresh
water coolant. A zinc anode is located
in
the raw water por-
tion
of
the exchanger to help control the effects
of
electroly-
sis. This area
of
the exchanger should be periodically
inspected and cleaned. To keep the exchanger operating effi-
ciently,
it
should be removed from the engine every 1000
hours to be thoroughly cleaned and pressure tested.
PETCOCK
CLEAN
OUT
DEBRIS
HEAT
EXCHANGER
NEW
REPLACE REPLACE
CLEAN
ZINC
ANODES
AND
REUSE
The
raw
water
pump
is
a self-priming pump with a non-fer-
rous housing and a Neoprene impeller. The impeller has flex-
ible vanes which wipe against a curved cam plate within the
impeller housing, producing the pumping action. The raw
water pump impeller should be checked every
500 operating
hours for wear. Should the pump fail,
it
can be disassembled
and overhauled. Check for internal wear within the pump
such as the cover plate, cam and impeller housing. Replace
components that show excess wear.
Engines & Generators
44
.
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