The operation of the two-stage regulator is similar
ACETYLENE CYLINDERS.--Acetylene stored
in principle to the single-stage regulator. The difference
in a free state under pressure greater than 15 psi can be
is that the total pressure decrease takes place in two
made to break down by heat or shock, and possibly
steps instead of one. On the high-pressure side, the
explode. Under pressure of 29.4 psi, acetylene becomes
pressure is reduced from cylinder pressure to
self-explosive, and a slight shock will cause it to
intermediate pressure. On the low-pressure side, the
explode spontaneously. However, when dissolved in
pressure is reduced from intermediate pressure to
acetone, it can be compressed into cylinders at
working pressure. Because of the two-stage pressure
pressures up to 250 psi.
control, the working pressure is held constant, and
The acetylene cylinder (fig. 6-27) is filled with
pressure adjustment during welding operations is not
porous materials, such as balsa wood, charcoal, and
required. A two-stage regulator is shown in figure 6-26.
shredded asbestos, to decrease the size of the open
The acetylene regulator controls and reduces the
spaces in the cylinder. Acetone, a colorless, flammable
acetylene pressure from any standard cylinder that
liquid, is added until about 40 percent of the porous
contains pressures up to 500 psi. It is of the same
material is filled. The filler acts as a large sponge to
general design as the oxygen regulator, but it will not
absorb the acetone, which, in turn, absorbs the
withstand such high pressures. The high-pressure
acetylene. In this process, the volume of the acetone
gauge, on the inlet side of the regulator, is graduated
increases as it absorbs the acetylene, while acetylene,
from 0 to 500 psi. The low-pressure gauge, on the outlet
being a gas, decreases in volume. The acetylene
side of the regulator, is graduated from 0 to 30 psi.
cylinders are equipped with safety plugs, which have a
Acetylene should not be used at pressures exceeding 15
small hole through the center. This hole is filled with a
metal alloy, which melts at approximately 212F or
psi.
releases at 500 psi. When a cylinder is overheated, the
ACETYLENE.--Acetylene is a fuel gas made up
plug will melt and permit the acetylene to escape before
of carbon and hydrogen. It is manufactured by the
a dangerous pressure can build up. The plughole is too
chemical reaction between calcium carbide, a gray
small to permit a flame to burn back into the cylinder if
stone like substance, and water in a generating unit.
the escaping acetylene should become ignited.
Acetylene is colorless, but it has a distinctive odor that
can be easily detected.
WELDING TORCHES.--The oxyacetylene
welding torch is used to mix oxygen and acetylene gas
Mixtures of acetylene and air that contain from 2 to
in the proper proportions, and to control the volume of
80 percent of acetylene by volume will explode when
these gases burned at the welding tip. The torch has two
ignited. However, with suitable welding equipment and
needle valves, one for adjusting the flow of acetylene
proper precautions, acetylene can be safely burned with
oxygen for welding and cutting purposes. When burned
with oxygen, acetylene produces a very hot flame that
has a temperature between 5,700F and 6,300F.
Figure 6-27.--Acetylene cylinder.
Figure 6-26.--Two-stage regulator.
6-20
