SECTION II. EQUIPMENT DESCRIPTION AND DATA (Con't)
1-8. EQUIPMENT CHARACTERISTICS, CAPABILITIES, AND FEATURES (Con't).
j. TUBES AND FLAPS.
(1) Tube Description. Standard tubes are circular rubber containers that fit inside the tire
and hold the air that supports the vehicle. Though strong enough to withstand only a few pounds of
pressure when not confined, the tube bears extremely high pressures when enclosed in a tire and wheel
assembly. Tubes are made of comparatively soft rubber and can be easily chafed, pinched, punctured,
or otherwise damaged. Standard tubes are generally made of a synthetic rubber called butyl, which has
air retention properties superior to natural rubber.
(2) Flap Description. Flaps are circular in shape and fit inside a tire assembly between the
tube and rim. The flap is made of a thicker, more durable synthetic rubber and protect the tube from
being chafed, pinched, punctured, or otherwise damaged from rim components.
(3) Tube Applications. All tubeless tires are required to be marked on the sidewall as
"tubeless." Never use tubes in a tire and rim assembly that is designated or marked tubeless. Tubeless
rims are designed to be airtight without a tube. Tubeless tires are built with an additional inner liner on
the inner cavity of the tire and adding a tube to a tubeless tire and rim assembly may cause the tire to
run hotter (because of the extra rubber mass).
k. VALVE STEMS.
(1) Valve Stem Description. Valve stems are either cured to or mounted on tubes or rim
bases for tubeless tires. Valve stems are used to admit or discharge air pressure from the tube or
tubeless tire cavity. The valve stem consist of a metal stem, a removable core that acts as a check
valve, and a valve cap. Construction is generally brass or brass with a rubber coating.
(2) Tube, Cured-on Valve Stems. Cured-on valve stems are non-removable and have a
rubber base that is vulcanized on the outer surface of the tube. There are two types of Cured-on stems:
the non--bendable, all-metal stem and the rubber covered stem, which is bendable when the stem is
longer than 3 inches (7.6 cm). Rubber covered stems have a rubber base vulcanized to the outer surface
of the tube and a rubber coated stem. All-metal stems have a rubber base vulcanized to the outer
surface of the tube and a bridge washer fastened to the base of the valve stem by a hex locknut.