LCAC-class ships, the APUs have sealed bearings,
LCAC-Class Ships
which do not require external lubrication.
The fifth model of ac generator, found only on the
Even though the lubricating oil systems installed on
LCAC-class ships, supplies 400-Hz, 120-to 208-volt ac
gas turbine-powered ships use a variety of oils, they all
power. You have already read about the LCAC electrical
have the same primary goals and basic system design.
power system in chapter 6 and earlier sections of this
The goal of all these systems is to provide cooling and
chapter.
lubrication to the generator bearings. Regardless of the
class of ship, the basic design of the lubricating oil
PHM-Class Ships
system is the same. The system draws oil from a sump
through a positive-displacement pump, where it is
The sixth model generator is installed only on the
pumped through an oil cooler (seawater cooled) and
PHMs and supplies the PHM-class ships with 400-Hz,
then through a filter assembly. Lubricating oil is then
450-volt ac power. You have already read about the
distributed to the generator bearings, and then (in most
PHM's electrical power distribution system in chapter 6
cases) gravity drained back to the sump.
and in earlier sections of this chapter.
DESIGN DIFFERENCES. Except for those on
the DDG-51 class ships, the majority of the generator
GENERAL MAINTENANCE AND
oil systems installed on gas turbine-powered ships are
REPAIR PROCEDURES
of this design. On the DDG-51 class ships, however,
three differences make the lubricating oil system unique
For the CG-, DD-, DDG-993, and DDG-51 class
from all of the other Allison generator sets. These
ships, probably 90 percent of all generator maintenance
differences are shown in figure 7-33. In the DDG-51
will be performed at the shipboard level. As a GSM, you
class ships, the first difference is that the generator
will be responsible for most of this maintenance. Only
shares the reduction gear oil system. The second
a small portion of the overall maintenance will be
difference is the installation of a generator scavenge
performed by the GSEs. In fact, the primary concern of
pump. The last difference is the installation of a jet
the GSEs will be to maintain the internal cleanliness of
pump eductor.
the external switches and their wiring connections. On
the other hand, as a GSM, you will be concerned with
Look closely at figure 7-33 and follow along as we
maintaining all of the generator's support components
describe the function of the jet pump eductor. Since the
and systems, including the lube oil and cooling systems.
generator no longer has its own sump, gravity draining
of the generator bearing housing is not very efficient, a
Because of the small number of design and
condition that could cause flooding of the bearing
operational differences among the models of the
housing. That is why a lube oil scavenging system was
generators installed on the CG-, DD-, DDG-993, and
DDG-51 class ships, the maintenance and upkeep of
installed. The pump, however, only operates when the
these generators and their associated systems will be the
generator is operating; therefore, the scavenging system
primary focus of our discussion. We will occasionally
only solves half of the problem. The other half of the
mention the LCAC, PHM, and FFG electrical systems.
problem was what to do with the excess oil during
For detailed information concerning these ships, we
prelube operations. That is why the eductor was
recommend you consult the appropriate technical
installed. Look again at figure 7-33. Notice that the
manuals.
prelube oil is used twice. Not only does it provide
sufficient pre-start lubrication for the reduction gear and
Lubricating Oil System
generator, it also powers the eductor that scavenges oil
from the generator oil return lines.
All of the generators installed on the CG-, DD-,
Now that we have briefly discussed the basic system
DDG-993, and DDG-51 class ships use 2190 TEP oil
operations and some of the system design differences,
for bearing lubrication. Except for those installed on the
let's move on and discuss some of the common
DDG-51 class ships, all of these generators have their
maintenance and repair procedures you will probably be
own independent oil sump. On the DDG-51 class ships,
required to perform.
the generators share the lubricating oil that also supplies
TESTS AND INSPECTIONS. All generator tests
the reduction gear. On the FFG-class ships, however, the
and inspections, if not performed during the normal
generators use 9250 (diesel) oil. On the PHM-class
watch routine, will be covered in the PMS.
ships, the SSPUs use 23699 oil for lubrication. On the
