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