pump. The system controls allow either electric
return excess system flow to the LO sump tank.
pump to be designated NORMAL with the other
The valve is fully open at a sensed pressure of 20
psig. Control air from the ship's LP vital air main
designated as STANDBY. The normal pump runs
at low speed only for preheating the LO and runs
is used for the operation of this valve.
at high speed during normal operating conditions.
With the pump controller mode switch in the
Temperature Regulating Valve
AUTO position, operation of the pumps is
controlled by a set of pressure switches. If the oil
This air pilot-operated valve is located at the
pressure to the reduction gear hydraulically most
inlet to the LO cooler and regulates the amount
remote bearing begins to drop below 13 psig, a
of oil flow through the cooler. The temperature
pressure switch closes and causes the standby
sensing element is mounted in the oil supply
pump to start operating at low speed. If the oil
piping to the reduction gear. Based on the signal
pressure continues to drop below 11 psig, another
from the temperature sensor, the valve regulates
pressure switch closes and the standby pump
the amount of flow through the cooler and
switches to high speed. A further drop in pressure
bypasses the rest. The valve is set to maintain a
to 9 psig closes a third pressure switch. It also
110 5F oil temperature to the reduction gear.
causes the air-motor driven coast down pump to
Control air from the ship's LP vital air main is
start operating by opening the solenoid valve to
used for operation of this valve.
the coast down pump air motor.
When the oil temperature is below 90F,
Lube Oil Cooler
preheating of the oil is required. A connection to
the lube oil fill, transfer, and purification system
The LO coolers are designed to maintain the
allows use of one of the LO service pumps to
LO temperature at 110 5F. The coolers on the
circulate oil through the LO purifier heater.
different class ships have physical differences, but
Priming lines are provided at each pump so that
they function the same. We will describe these
the operation of either service pump will maintain
differences in the following paragraphs.
a continuous oil prime to the other two pumps.
CG, AND DD LUBE OIL COOLER.--
A relief valve set at 80 psig is located at each
service pump discharge to protect the system from
A LO cooler is installed in each LO service system
overpressurization.
downstream from the LO pumps. The cooler has
If the propeller shaft is rotating during an
a shell assembly, a tube bundle, and inlet and
electric power failure on the ship, the electric
outlet water boxes. The cooler is a single-pass shell
pumps stop. This loss of pressure causes the LO
and tube type of heat exchanger. Seawater is used
coast down pump to start and continue to run
as the cooling medium. It enters the inlet water
box through the inlet connection, makes one pass
until the propulsion plant can be secured. The
duration of operation of this pump is limited by
through the tubes, and is discharged through the
outlet water box. Seawater flow is regulated by
the quantity of air stored in the HP air flasks
provided in the engine room. The discharge of the
a pneumatically operated valve controlled by a
temperature sensor installed in the LO piping
coast down pump goes into the reduction gear oil
inlet header via the LO service filter. The
downstream from the cooler. The LO inlet is at
discharge bypasses the rest of the LO service
the opposite end from the water inlet, resulting
system. If the electric pumps restore normal
in counterflow heat transfer.
system pressure to 15 psig, a pressure switch opens
and the air solenoid valve that controls air flow
FFG LUBE OIL COOLER.--This cooler is
to the pump motor closes and stops the coast
made of two shell and tube type of heat
down pump. The coast down pump also stops if
exchangers piped in series. Seawater from the
main seawater cooling system circulates through
the propulsion shaft stops rotation.
the tubes in a single pass through each shell of
the cooler in series. The LO flows through each
Unloading Valve
shell in series. The oil enters the cooler through
the upper shell and leaves the cooler through the
This air pilot-operated valve senses the oil
lower shell. Vent connections are provided on
pressure at the reduction gear hydraulically most
both the upper shell and water box, and drain
remote bearing and regulates the oil supply flow
to maintain 15 psig at that bearing. If the sensed
connections are provided on the lower shell and
water box.
pressure exceeds 15 psig, the valve will open and
4-9
