engine start is reduced to 250 psig by the HP
equipment and pneumatic controls. It supplies
reducing valve and then to 85 psig through a series
purified LP air to the electronics and to the HP
o f orifices. The ships do not have HP
air system dryers. Some uses of LP air in the
engineering plant include the following areas:
air start capability for its main engines. The CG-
class ships have air pressures of 220 psig through
FO fill and transfer compensating system
the reducing valves and 45 psig through the
orifices. All ships have HP air start capability for
the ships' generators. The 3000 psig of air is
WHB control air
reduced to starting pressure by the start air valve.
The 3000 psig of air is also used to back up the
Seawater temperature control valves
LP air supply through a reducing station in the
No. 1 engine room. The pressure varies between
FO coalescer
ships. For the proper setting, consult your ship's
Clutches and/or brakes
EOSS.
FFG LOW-PRESSURE AIR SYSTEM
The system has LP air compressors, air dryers,
purifiers, main receivers, and a piping system. The
The SS air is provided by two LP, screw-type
piping system has valves, reducing stations, and
compressors that have a capacity of 100 scfm at
connections necessary to distribute compressed air
a discharge of 125 psig. The compressors provide
to various services. A reducing station is provided
air to a vital air main, a nonvital air main, and
in the HP air system to supplement the SSAS
a loop branching off the vital air main that
when compressed air consumption exceeds ship's
supplies air to electronics equipment. Dry air is
compressor output. Automatic shutoff valves,
delivered to the electronics equipment by the
called priority valves, are installed downstream
processing of air from the vital main through
from all mission essential (vital) equipment and
dehydrators. The vital air main piping is cross
upstream from all nonessential (nonvital) services.
connected between the two compressors and
If air pressure falls below a prescribed setting,
provides control air to the vital services in the
these valves close and eliminate use of non-
machinery spaces. The nonvital services are fed
essential services during the reduced pressure
from the nonvital air main through priority valves.
period.
The priority valves are located between the vital
Ships have so many variations as to the type
and nonvital air mains. These priority valves are
and number of compressors, the system pressure
settings, and priority valve settings that we will
designed to shut off air to the nonvital air main
if the demands on the whole system (vital and
not attempt to cover this material. Refer to the
nonvital) are greater than the compressors can
ship's equipment technical manuals and EOSS for
provide and if the pressure falls to 85 psig.
a more in-depth description of each individual
A cross connection through a manifold reduc-
system.
ing station automatically provides HP air to the
vital air main. The HP air at 3000 psi is reduced
CG, AND DD,
to the SSAS pressure and thereby backs up the
HIGH-PRESSURE AIR SYSTEM
vital air main. The reducing station is set at
80 psig so it will deliver air when the vital main
The HP air system provides HP air to the
has dropped to 80 psig.
weapons systems, aviation equipment, gas turbine
starting, and backup air for the SSAS. The system
FFG HIGH-PRESSURE AIR SYSTEM
has two compressors that supply 3000 psig of air
to the storage flask. The air then goes into the
The FFG HP air system has two HP air
system through a dehydrator. The dehydrator
compressors capable of providing 3000 psig to the
provides moisture-free, oil-free, and contaminant-
system. Each compressor is provided with an air
free air to the system.
dehydrator to remove solid contaminants and
The HP air system is primarily maintained by
particulate and vaporous water and oil from
A Division. As a GS, you will find it is used in
the air. An air flask is installed at each
the engine room as the primary/emergency air
compressor downstream of the dehydrators. The
start for the ship's main engines and generators.
air compressors are designed for continuous
The HP air flasks are located in each engine room
automatic operation. A pressure switch located
and the No. 3 generator room. Air for the main
4-22