very clean because the oil stored in them can go
seawater. This is because they are in solution.
directly into either the MRG or the CRP system.
Water, however, can be separated from oil
Lube oil levels within these tanks are
because water and oil are immiscible (incapable
monitored by a liquid level indicating system. The
of being mixed). Also, the specific gravities of the
materials to be separated must differ. Particle size,
and the indicating meter.
fluid viscosity, and length of the centrifuge period
The transmitter is the level detector unit
influence the effectiveness of the centrifugal
mounted vertically within the tank by brackets or
process. In general, the greater the difference in
flanges. A magnet-equipped float moves along the
specific gravity between the liquids to be separated
and the lower the viscosity of the oil, the greater
causes the meter to show the number of gallons
the rate of separation. Lube oils are heated before
of oil in the tank.
being centrifuged to decrease their viscosity.
Storage tanks are nothing more than small
Centrifugal purifiers used on naval ships have
enclosed compartments with fill and suction
bowls of two types, tubular and disc. Refer to
piping connected to them. These storage tanks
volume 1, chapter 7, of this TRAMAN series, for
also have overflow piping attached to prevent
additional information on these purifiers.
overfilling and overpressurizing the tanks.
Settling tanks are similar to storage tanks
1. Tubular type. The tubular type has a small
except that they have heating coils installed in
diameter and rotates at a comparatively high
them to speed up the settling process. Settling
speed. The bowl has a three-wing device that keeps
tanks allow the oil to stand while accumulated
the liquid rotating at the speed of the bowl and
water and other impurities settle to the bottom.
prevents slippage. The tubular bowl is fed through
The settling action is caused by the difference in
a nozzle at the bottom.
specific gravity of the impurities and oil. The force
2. Disc type. The disc type is large in diameter
and rotates at a comparatively lower speed. This
to form at the bottom of the tank; the number
bowl is fitted with a series of discs that separates
of layers depends on the different specific gravities
the liquid into thin layers. Liquid is ordinarily fed
directly toward a series of holes punched through
the disc stack; the liquid flows upward through
up the settling but also increase the efficiency of
these holes, depending on specific gravity.
In Navy ships, combined storage and settling
tank capacity is two times the combined capacity
In both the tubular and disc types, separated
of the involved LO sumps. The recommended LO
oil moves toward the center for discharge into one
storage on hand is one for one; that is, for each
of the covers; the separated water moves toward
gallon of sump capacity, a gallon should be in
the outside and is delivered from the bowl into
the other cover. Solids separated from the liquids
are retained in the bowls.
LUBE OIL PURIFIERS
Some ships are being outfitted with a self-
cleaning centrifugal purifier whose operation is
Centrifugal purifiers, frequently called cen-
similar to the self-cleaning FO purifier. It is
trifuges, are used extensively in naval service to
remove LO impurities. A centrifuge is a bowl or
more than 0.3 percent water and not more than
0.02 percent solids.
hollow cylindrical vessel that rotates at high speed
while a liquid (in this case contaminated oil) passes
Purification of Lube Oil
through it. The centrifugal force created by the
high rotative speed acts perpendicular to the axis
of rotation and causes solid impurities to be
The purity of LO is essential to the operation
of the ship's machinery. Dirt, sludge, water, or
deposited on the bowl's inner surface. Water
entrained in the oil is segregated in a layer
and scratch metal surfaces. Contaminants in oils
used for hydraulic applications, such as in the
CRP system, could clog small ports and filtering
are insoluble in one another. For example,
mechanisms in the controls.
Two primary methods of purification are in
gasoline and diesel fuel cannot be separated from
use at the shipboard level. One method is the
LO; likewise, salt cannot be removed from