MARINE WATER PUMPS
Two types of marine water pumps are in general use:
the metal impeller pump and
the
neoprene impeller
pump. Each pump has certain advantages and dis-
advantages (see Table
3)
and both are used exten-
sively with marine cooling systems. Two types of
pumps are necessary because water pumps are used
to perform different functions, depending on the type
of cooling system and the operating conditions.
Metal impeller pumps provide no suction lift but can
operate in hot, cold, or dirty water. Neoprene impeller
pumps provide a suction
lift,
but can be used only
with clean, cool water.
The metal impeller pumps are used for captive water
systems, and the neoprene impeller pumps are used
for sea water systems.
All
captive water system
pumps (metal impeller) are driven by
a
V-belt from
the engine crankchaft.
All
sea water pumps (neo-
prene impeller) for the J-series (except
MDJE,
Spec
AB)
are gear driven.
Captive Water Pump
Periodically check the captive water pump forwear or
signsof leakage from theshaft seal. Loosen thedrive
belt and move the water pump pulley back and forth.
The pulley should be tight on the shaft and
only
a
slight amount of bearing play should be felt. Rebuild
the pump if wear is excessive or if the seal leaks. Refer
to the section on
Water
Pumps
for water pumps
service procedures.
Sea Water
Pump
Periodically check the sea water pump for signs of
leakage from the shaft seal.
A
leaking shaft seal may
allow water to enter the crankcase and contaminate
the engine oil. Remove the pump end cover (see
Figure
18)
and inspect the impeller for cracking or
signs
of
wear. The impeller deteriorates with time
because of continuous flexing and must be period-
ically replaced. If the impeller fails, check for pock
marks on its end surfaces. This indicates that air has
been entering cooling system, reducing pump lubri-
cation and causing overheating. Check
all hose
connections for leaks that could admit air, and
tighten
as
required. If
the
impeller fails after short
service (under500 hours),
checkforpossibledefects.
If impeller blades have broken, locate and remove the
particles or they will impede water flow. When re-
installing, coat the impeller with grease, and make
certain the impeller cover is air-tight. Tighten the
cover screws to 15-17 inch-pounds (1.70-1.92 Nm).
Refer to the section on
Water
Pumps
for water pump
service procedures.
FIGURE
18.
END
COVER
REMOVAL
WATER PUMP REPAIR
This section covers removal, repair, and installation
procedures for all metal impeller and neoprene
impeller water pumps used with Onan marine liquid-
cooled engines. Repair Kits are available for most
water pumps. Table
3
shows the water pumps used
with Onan marine liquid-cooled engines. Metal
impeller pumps are required for circulating HOT
engine coolant. They are most commonly used with
marine cooling systems that use a heat exchanger.
Neoprene impeller pumps may be used only for
pumping
COOL water because the impeller deterio-
rates rapidly
in
hot water. They are most commonly
used for pumping sea water in marine cooling
systems.
24
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by any means, is strictly prohibited.
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