operate at pressures above 500 psi. Hydraulic systems
from the tank, salt water reenters from the gravity tank
may operate at pressures as high as 3000 psi. Those
or from some other source of salt water supply. The
with maximum design pressures in excess of 300 psi
storage tank is thus kept completely filled at all times,
may be fabricated from stainless steel tubing or from
preventing the formation of gasoline vapor.
the copper or steel used for lower pressure systems.
Some ships are provided with a specially
constructed inert-gas piping system for lines running
GASOLINE SYSTEMS
inside the ship. A double-pipe gasoline line is formed
by running brass piping inside a steel tube, and filling
Gasoline is a highly volatile mixture of liquid
the space between with an inert gas. The brass piping
hydrocarbons. It is used as a fuel for internal
carries the gasoline. The free passage of the inert gas
combustion engines in aircraft, automotive equipment,
throughout the system is ensured by installing bypass
and various other applications. Gasoline vapor, when
tubes at each joint.
explosive mixture which can be set off by a slight spark
COMPRESSED AIR SYSTEMS
or flame. Gasoline vapor is heavier than air. Therefore,
it tends to collect at the bottom of storage spaces or it
Air is a mixture (not a chemical combination) of
may travel along an air current a considerable distance.
several gases. The most important of these are nitrogen
If the vapor is then ignited, it flashes back to the source,
and oxygen, with small amounts of argon and neon.
causing an explosion. If liquid gasoline is present along
Compressed air is neither poisonous nor
with the vapor, the explosion is followed by fire. The
flammable, but it should be handled carefully. Air
volatility of gasoline is demonstrated by the fact that
tanks, lines, and fittings can rupture from too much
one quart of uncovered gasoline upon complete
pressure. Carelessness with compressed air can also
evaporation will mix with 520 cubic feet of air to form
cause eye injuries.
an explosive mixture. This amount of air is normally
contained in a space 10 by 6 l/2 by 8 feet. Air can
Compressed air systems are fabricated from brass
absorb 28 percent gasoline vapor at normal atmospheric
and copper piping materials, bronze silver-brazed
pressure. However, an explosive mixture exists only
fittings, and bronze valves. Moisture and oil must be
when the percentage of gasoline vapor in the air is
kept out of compressed air systems. Moisture is
between 1.4 and 2.5 percent.
damaging to the piping and causes excessive wear in
air-operated equipment. Oil is dangerous in
Remember that gasoline is not only a potential
high-pressure (600 psig and above) compressed air
source of an explosive mixture, but is also a toxic
systems because it can form an explosive mixture with
hazard. Keep it away from your skin, and do not inhale
the air. Oil and moisture separation filters and, where
the vapors. Do not smoke or use naked lights in the
necessary, air dryers are provided to remove these
vicinity of gasoline.
contaminating substances from the system.
Remember also that a leaktight gasoline piping
The major air systems found aboard ship are (1) the
system is essential to the safety of your ship. To ensure
high-pressure air system, (2) the ship's service air
that gasoline piping systems are leaktight, inspect all
system, (3) gas ejecting systems, (4) starting and control
joints and valves frequently. Always use nonsparking
systems for diesel engines, and (5) combustion control
tools when you are repairing gasoline piping systems.
air systems.
Some ships have a gasoline system designed to
prevent explosions resulting from the ignition of
The High-Pressure Air System
gasoline vapor during the fueling of aircraft and small
boats. This system may be either an inert-gas blanket
The high-pressure air system provides air at 3000
system or a saltwater displacement system. In the first
psi or 4500 psi for charging air banks. This system is
type, inert gas is admitted to the storage tank and forms
also used at required pressure for services such as
a blanket over the gasoline, thus preventing the
counterrecoil, diesel engine starting, gas ejection,
formation of an explosive vapor. In the second type, the
torpedo charging, and torpedo workshops. When the
storage tank is first filled with salt water so that all air
service requires air at less than 3000 psi, the outlet from
is excluded. Then gasoline is pumped into the tank,
the high-pressure system is equipped with a reducing
forcing a corresponding amount of salt water out at the
valve.
bottom and into a gravity tank. As gasoline is pumped
15-48