Figure 4-5.Acetylene cylinder.
225 cubic feet of acetylene. Just because a cylinder has
a 225-cubic-foot capacity does not necessarily mean it
has 225 cubic feet of acetylene in it. Because it is
dissolved in acetone, you cannot judge how much acety-
lene is left in a cylinder by gauge pressure. The pressure
of the acetylene cylinder will remain fairly constant until
most of the gas is consumed.
An example of an acetylene cylinder is shown in
figure 4-5. These cylinders are equipped with fusible
plugs that relieve excess pressure if the cylinder is
exposed to undo heat. The standard Navy acetylene
cylinder contains 225 cubic feet of acetylene and weighs
about 250 pounds. The acetylene cylinder is yellow, and
all compressed-gas cylinders are color-coded for iden-
tification. More on the color coding of cylinders is
covered later in this chapter.
MAPP (methylacetylene-propadiene) is an all-pur-
pose industrial fuel having the high-flame temperature
of acetylene but has the handling characteristics of
propane. Being a liquid, MAPP is sold by the pound,
rather than by the cubic foot, as with acetylene. One
cylinder containing 70 pounds of MAPP gas can accom-
plish the work of more than six and one-half 225-cubic-
foot acetylene cylinders; therefore, 70 pounds of MAPP
gas is equal to 1,500 cubic feet of acetylene.
Total weight for a MAPP cylinder, which has the
same physical size as a 225-cubic-foot acetylene cylin-
der, is 120 pounds (70 pounds which is MAPP gas).
MAPP cylinders contain only liquid fuel. There is no
cylinder packing or acetone to impair fuel withdrawal;
therefore, the entire contents of a MAPP cylinder can be
used. For heavy-use situations, a MAPP cylinder deliv-
ers more than twice as much gas as an acetylene cylinder
for the same time period.
Because of its superior heat transfer characteristics,
MAPP produces a flame temperature of 5300°F when
burned with oxygen. MAPP equals, or exceeds, the
performance of acetylene for cutting, heating, and braz-
MAPP is not sensitive to shock and is nonflamma-
ble in the absence of oxygen. There is no chance of an
explosion if a cylinder is bumped, jarred, or dropped.
You can store or transport the cylinders in any position
with no danger of forming an explosive gas pocket.
The characteristic odor, while harmless, gives warn-
ings of fuel leaks in the equipment long before a dan-
gerous condition can occur. MAPP gas is not restricted
to a maximum working pressure of 15 psig, as is acety-
lene. In jobs requiring higher pressures and gas flows,
MAPP can be used safely at the full-cylinder pressure
of 95 psig at 70°F. Because of this, MAPP is an excellent
gas for underwater work.
Bulk MAPP Gas
Bulk MAPP gas facilities, similar to liquid oxygen
stations, are installed at some activities where large
supplies of the gas are used. In bulk installations, MAPP
gas is delivered through a piping system directly to the
user points. Maximum pressure is controlled centrally
for efficiency and economy.
Cylinder-filling facilities are also available from
bulk installations that allow users to fill their cylinders
on site. Filling a 70-pound MAPP cylinder takes one
man about 1 minute and is essentially like pumping
water from a large tank to a smaller one.
MAPP Gas Safety
MAPP gas vapor is stable up to 600°F and 1,100
psig when exposed to an 825°F probe. The explosive
limits of MAPP gas are 3.4 percent to 10.8 percent in air
or 2.5 percent to 80 percent in oxygen. As shown in