COOLING FAN(S).--The fan(s) is located in
the cooling air duct between the flow modulator
and the fire damper. The fan(s) draws air from
the intake duct through the flow modulator. It
blows the air through the fire damper to the
module enclosure. The air enters the module
through the silencer. It passes across the ceiling-
mounted baffle within the enclosure and then
circulates around the engine. It exits through a
gap between the engine exhaust nozzle and the
exhaust eductor where it mixes with the engine
exhaust.
COOLING FAN CONTROLLER.--The fan
controller has a circuit to cycle the fan on and off
Figure 3-7.--No. 3 exhaust configuration.
automatically based on the enclosure temperature.
It also has circuitry to perform a GTGS system
fire stop, which is described later in this chapter.
engine (fig. 3-7) traverses the ship and discharges
It is provided with a NORMAL/ALTERNATE
from the aft, port side on the 01 level. Because
power supply selector switch. The NORMAL
of the location of the No. 3 exhaust, a seawater
source for the controller is the generator bus; the
trap is provided to trap and drain this water
ALTERNATE source is one of the other SWBDs.
overboard.
The fan will cycle on when a temperature switch
within the module enclosure senses a temperature
SILENCERS. --The silencers have sound-
of 175F. It cycles off when the temperature
deadening material. They are encased in a
decreases to 160F. The model 139 also cycles on
perforated stainless steel sheet cylinder. This is
and off based on the enclosure temperature. This
suspended in the center of the exhaust duct. This
function is controlled by the LOCOP; however,
unit with the duct wall insulation provides the
no separate fan controller is used.
required sound reduction to meet airborne noise
requirements.
FIRE DAMPER.--The fire damper is located
in the cooling air duct between the fan and module
BOUDARY LAYER INFRARED SUPPRESSION.
enclosure. It closes off the flow of cooling air to
--The purpose of the IR suppression system is to reduce the
the module when a fire is present within the
exhaust gas temperature before it is discharged
module. During normal operation, the fire
to the atmosphere. This minimizes heat sensing
damper is in the full-open position. A fire detected
of the ship by other vessels and aircraft.
by either of the two UV detectors within the
enclosure will cause the fire stop circuit within the
fan controller to close a set of contacts. This
energizes the fire damper motor and rotates the
damper to the closed position. The fire damper
is reset manually.
Exhaust Duct System
The exhaust ducts are round, insulated,
stainless steel structures. Each duct has a silencer
GREEN WATER TRAP.--Figure 3-7 shows
and an IR suppression system. The model 139 uses
the location of the green water (seawater) trap.
a BLISS-type IR suppression system similar to the
Because of the low location of the No. 3 engine
ones used on the CG main engines. Because of
exhaust duct exit relative to sea level, green water
their smaller size and lower gas flow rate, they
can enter the duct exit during high sea states. To
do not require eductors as do the main exhaust
stop the seawater from flowing down through the
ducts. The exhaust ducts from the No. 1 and No.
exhaust system, a tank is located in the duct near
2 engines run parallel to the main engine ducts
the exit. Any water that enters the duct is trapped
in the exhaust stacks. The duct from the No. 3
in the tank and drained overboard.
3-9
