Section V. TUBES
32-14. Types of Tubes.
32-15. Tube Flaps. Tube flaps (fig. 32-22) usually are
constructed of a strip of semihard rubber with tapered
ends that form a circle. Flaps are required in tube-type
a. Standard. Standard tubes (fig. 32-19) are
tires that are used on flat-base rims. They protect the
circular rubber containers that fit inside the tire and hold
tube from being pinched between the tire bead and the
the air that supports the vehicle. Though it is strong
rim and from irregularities on the base of the rim.
enough to stand only a few pounds of air pressure when
not confined, the tube bears extremely high pressures
32-16. Types of Valves.
when enclosed in a tire and wheel assembly. Because
the tube is made of comparatively soft rubber to fulfill its
function, it is easily chafed, pinched, punctured, or
a. Cured-On Valve.
otherwise damaged. Standard tubes generally are made
of butyl, a synthetic rubber that has air-retention
(1) Rubber-Covered Valve. Cured-on valve
properties superior to natural rubber. Standard tubes are
stems (fig. 32-23) have a rubber base that is vulcanized
made of one layer of rubber molded in the shape of a
on the outer surface of the tube and cannot be removed
doughnut. They are used regularly for standard tires.
unless it is cut off for replacement. The rubber-covered
stem is bendable when the stem is longer than 3
b. Combat. Combat tubes (fig. 32-20) are
constructed the same as standard tubes except that they
are smaller than standard tubes with the same size
(2) All-Metal-Stem Cured-On Valve. This valve
markings. Because the inside cross section of combat
(fig. 32-24) is mounted to the tube the same way as the
tires is smaller, combat tubes only will be used with
rubber-covered valve, but this type uses a nonbendable,
combat tires. However, in the event that combat tubes
all metal stem.
are not available, it is permissible to use the next size
smaller standard tube.
b. Cured-On Large-Bore Valve. Cured-on large-
bore valve stems generally are used on tubes for very
c. Bullet Resisting. Bullet-resisting tubes (fig. 32-
large tires such as for earthmovers. The large bore
21) are of a heavy, thick construction that automatically
permits rapid inflation and deflation of tubes. Except for
seals bullet punctures.
Bullet-resisting tubes are
size, they are similar to the cured-on valve described
identified by their extra weight and thickness and
generally have green-painted valve stems.
c. Cured-In Valve. Cured-in valve stems (fig. 32-
25) are similar to cured-on valve stems except that the
rubber base is inverted and vulcanized to the inner
surface of the tube. The rubber base also may be
vulcanized directly to the rubber body of the tube.
Figure 32-20. Combat Tubes.
Figure 32-19. Standard Tube.