icing condition exists when the inlet air
bleed air system on a DD-class ship, as we describe
temperature to a GTE is 41F or less and the
the system.
humidity of the inlet air is 70 percent or greater.
Bleed air is taken from any operating GTE and
Bleed air from the header enters the anti-icing
generator through a bleed air regulator valve,
system piping for each GTM and GTGS and is
which reduces the pressure to 75 psig. It then
directed to the anti-icing, air-flow regulator
enters the header. The various valves that
valves. The forward and after bleed air header
control the flow can be operated from the PACC
risers provide the hot bleed air for each GTM and
in CCS or the PLCC in the engine room. The
GTGS in the No. 1 and No. 2 engine rooms. The
AUTO MODE can be used to automatically set
bleed air header in the No. 3 generator room
the valves in sequence during GTE start, or they
provides the hot bleed air for the No. 3 GTGS.
can be sequenced individually by the operator.
The anti-icing, air-flow regulator valves control
The operator can also operate the valve manually
the flow of hot bleed air into the intake of each
by overriding the electrical signal at the valve.
GTE. This maintains the temperature of the
Bleed air for starting goes through two
inlet air to each GTE at 38F, or greater, during
separate pipes. Hot bleed air flows to the mixing
engine operation. Each valve is a double-
valve through the high-temperature bleed air
pneumatic, piston-actuated, butterfly-vane,
valve. Bleed air also flows through the masker air
regulating valve. This valve is electronically
valve through the masker air cooler where it is
controlled by an associated anti-icing temperature
cooled to about 190F. The cool bleed air then
controller. These controllers are enabled or
flows through a filter to remove any solid
disabled by the seven anti-icing ON/OFF push-
contaminants and then to the masker/start
button switch indicators on the PLCC and
transfer valve. I n the start position the
PACCs. (NOTE: This system is described as it
masker/start transfer valve allows the cool bleed
currently exists. SHIPALTS have been issued that
air to flow to the mixing valve. In the mixing
remove the electronic controls of the valves and
valve, the hot bleed air and cool bleed air are
make them manually operated.)
mixed to maintain a temperature of about 400
The controller used to operate the anti-icing
to 450F. Air then flows through a start air filter
valve for each GTE intake combines and
and then to the motor air-regulator valve. The
compares three signals with the fixed temperature
motor air-regulator valve regulates start air at 45
signals. The three input signals are CIT, NG G, and
psig for starts and 22 psig for motoring. Another
bulk air temperature. The fixed temperature
valve in the start system is the mixing bypass valve.
signals are 38F or bulk air temperature. The
This valve allows only the cool bleed air to pass
comparison of these signals determines the
to the starter during motoring.
torque motor control positioning signal. This
Start air on the FFG-class ships flows from
signal drives the anti-icing valve torque motor,
the GTE into a common header through a
which positions a poppet valve in the valve's
reducing valve where it is reduced to 75 psig. It
pneumatic regulating control assembly. The
then passes through the bleed air cooler, which
poppet valve, in turn, regulates the amount of
maintains the air at a temperature of about 400F;
pressure the 100 psig ship's service (SS) air can
from there it passes to the start air system and
exert on the valve's pneumatic actuating pistons;
to the motor air-regulator valve. This valve
the position of the pistons determines the valve
operates the same as on the CG-, and DD-
setting. When SS air pressure on the pistons is not
class ships.
working, a spring in the valve's actuator assembly
maintains the valve's butterfly vane in the closed
ANTI-ICING AIR SYSTEM
position.
When the GTM anti-icing temperature
The anti-icing systems on the CG-, and DD-
controller is enabled, it maintains the temperature
class ships differ greatly from the FFG-class
of the inlet air in the intake at 38F. The controller
ships. We will describe these systems separately.
maintains this temperature by comparing bulk air
temperature to the controller's 38F fixed
CG, and DD Anti-Icing System
temperature reference. However, when changes
in engine speed are made, the speed sensor (NG G)
The gas turbine anti-icing systems take hot
signals the controller to complement immediately
bleed air from the bleed air header and distribute
the increase or decrease in intake air flow with
it to each GTM and GTGS intake to prevent the
a corresponding increase or decrease in hot bleed
formation of ice under an icing condition. An
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