A manhole cover is provided in the top of each
tank to gain access for cleaning and maintenance. A
Buns-N-Cork gasket is installed between the tank and
manhole cover plate to prevent leakage. The outer
tank manhole cover plate is fitted with a steam-out
The seawater supply riser enters the outer tank at
the top and terminates in a diffuser near the bottom.
The seawater required for pressurizing the tanks is
discharged through this line.
A pressure gage line extends from the top of the
outer tank to a pressure gage located in the pump
room. The gage has a red pointer, indicating the maxi-
mum allowable tanktop pressure for that set of tanks.
(Allowable pressures will vary for the different
classes of ships.) A warning plate attached near each
gage reads, THE MAXIMUM ALLOWABLE
TANK-TOP PRESSURE INDICATED BY THE
FIXED RED POINTER SHALL NOT BE EX-
CEEDED WHEN THE SHIP IS FUELED.
Two in-tank reservoirs for water-filled, static-
head gasoline gages are installed in the outer tank.
One reservoir is installed at the top of the tank and the
other at the bottom directly underneath the upper
reservoir. Stuffing boxes are provided where the tub-
ing for the gage passes up through the outer tank. The
stuffing boxes prevent leakage of gasoline and seawa-
ter out of the tank. They also prevent nitrogen in the
cofferdam from entering the tanks.
LPDs have water filled, static-head gages
but are scheduled to have them replaced with
TLIs. LHAs already have TLIs.
The outer tank is interconnected with the drawoff
tank by a sluice pipe. The sluice pipe extends from
near the top of the outer tank and terminates in a
diffuser at the bottom of the drawoff tank. The top of
the sluice pipe is flared to reduce friction. The outer
tank completely envelopes the drawoff tank.
The outer tank has a motor-driven stripping sys-
tem installed for deballasting the tank. The inde-
pendent hand-stripping system also ties into the outer
tank to remove water and sludge from the bottom of
The draw-off tank is the smaller of the two tanks. It
is the tank from which gasoline is drawn when servicing
or off-loading fuel. It is the first tank filled when
MOGAS is being received and the last tank emptied
when MOGAS is being off-loaded.
The gasoline supply riser extends from the extreme
top of the drawoff tank to the common suction header
of the gasoline pump. The recirculating header termi-
nates in a diffuser at midpoint in the draw-off tank.
The draw-off tank is provided with an independent
stripping system to remove water and sludge from the
bottom of the tank. This system is the same hand-oper-
ated type used with the JP-5 service tanks. The suction
line is fitted with a shutoff valve and extends from
three-fourths of an inch off the bottom of the lowest part
of the tank. The discharge line, fitted with a sight glass,
test connection, one-way check valve, and a shutoff
valve, terminates in two places: 24 inches off the bottom
of the outer tank, and overboard.
The draw-off tank also has a water-filled, static-
head gage, or a TLI.
The drain tank is a small tank located inside the
outer storage tank. The drain tank stores contaminated
MOGAS/water that is filtered/separated out of the
The cofferdam provides two-fold protection for the
storage tanks. The cofferdam is normally kept charged
with nitrogen (Nz) to 3 psi at 50% inertness or carbon
dioxide (COZ) at 35% inertness to reduce fire and ex-
plosion hazards. It also collects any leakage from the
The nitrogen supply line for purging and charging
the cofferdam terminates in a loop, which completely
encircles the outer tank. From this loop (located near
the top of the cofferdam), pipes (legs) extend down to
near the bottom. Each leg is fitted with a diffuser, which
serves to spread the inert gas throughout the space. A
stop valve for controlling the nitrogen entering the tank
is located in the main supply line at the pump room
An air escape riser, fitted with a shutoff valve,
extends from the top of the cofferdam and vents to
atmosphere at the 02 level. A bypass line is installed
around the shutoff valve. This line contains a