ENGINEERING SUPPORT AND AUXILIARY
EQUIPMENT AND SYSTEMS
ships. The reciprocating type is rated at 200 cfm and is
As a GS or even an engineer, you should know the
important role the engineering auxiliary equipment and
installed on DD-963 and DDG-993 class ships.
systems play in the overall operations of the ship. Even
There are two LPACs installed on the DD-963,
though most of the support and auxiliary equipment are
DD-993, and FFG-7 class ships. Because of the ship
located in the engineering spaces, their systems extend
size, lower compressor capacity, and air volume
throughout the ship. For the most part, you and your
demand, there are three LPACs installed on the CG-47
shipmates may forget what services this equipment and
and DDG-51 class ships.
these systems provide until your telephone rings and the
captain is on the line telling you he has soap in his eyes
Normal Operation
and hair and no water to rinse with. As a GS, you are not
directly responsible for the making and distribution of
Gas turbine-powered ships will normally have at
fresh water. You are, however, responsible for the
least two LPACs aligned for operation to provide
production of the steam or electricity that is needed to
low-pressure air for maintenance, service, control,
operate the distilling plants.
pneumatic power, and other utility purposes. For those
This chapter will provide you with some basic
ships with only two compressors, the normal alignment
component descriptions for support and auxiliary
is to have one unit in constant run and the other in
equipment and their systems. It also will discuss
standby. However, if one unit is out of commission, then
operations, system interaction, and maintenance
only one unit will be available.
requirements. Because of the similarities in the
For those ships with three compressors, normal
equipment, system designs, and service requirements,
operations will have the cutout pressure switches set at
all the topics in this chapter will be discussed in general
125 psig, 120 psig, and 115 psig. The compressor run
terms.
status will depend on the pressure cutout selection. For
example, the compressor set at 125 psig will be in
constant run. The unit set at 120 psig will be designated
OPERATION AND MAINTENANCE OF
as intermittent. The third unit, set at 115 psig, will be in
SUPPORT AND AUXILIARY
emergency standby.
EQUIPMENT
Even though multiple units are installed on gas
The proper operation of and good maintenance
turbine ships, they may not all be needed during routine
practices for the support and auxiliary equipment should
operations. During normal operations, one compressor
be high on your list of priorities. Your attention to these
will usually provide sufficient air to supply the system.
priorities should minimize the need for telephone calls
Each LPAC has its own low-pressure air subsystem.
like the one we just described. In this section, we will
Each subsystem consists of the LPAC, a dehydrator, and
highlight some of the operational and maintenance
a main receiver. When in operation, each LPAC system
requirements that are crucial to the efficient
supplies air to a common vital air piping header. This
performance of the support and auxiliary equipment.
header usually runs longitudinally near the centerline of
the ship. The mission-essential equipment services are
LOW-PRESSURE AIR COMPRESSORS
isolated from the nonessential services by two priority
valves, which actuate at 85 psig. These priority valves
Basically, the reciprocating and helical screw are the
do not operate very frequentlyonly when they are
two types of low-pressure air compressors (LPACs)
needed. For example, if a large leak develops in the air
used on gas turbine-powered ships. The helical-screw
system, the priority valve will activate to maintain
type is the most widely used. It is rated at 100 cfm and
sufficient operating air pressure to mission-essential
is installed on the CG-47, DDG-51, and FFG-7 class
equipment. If the leak becomes too large for the priority
