SECTION II. EQUIPMENT DESCRIPTION AND DATA (Con't)
1-8. EQUIPMENT CHARACTERISTICS, CAPABILITIES, AND FEATURES (Con't).
l. VALVE STEM COMPONENTS.
Valve Cores. The valve core is assembled into the valve stem body and permits air,
under pressure, to enter but prevents it from escaping. There are two types of valve cores and two sizes
of each type. The two types are the visible spring type and the concealed spring type, and they are
interchangeable. Two sizes are provided for the standard bore and the large bore valve stems. The core
shell has a rubber washer that provides an airtight seal against the tapered seal inside the stem. Directly
below the shell is a cup that contains a rubber seat that, in the closed position, is forced against the
bottom of the shell forming an airtight seal. The pin on top of the valve core, when pushed down, forces
the cup away from the shell permitting air to flow.
Valve Caps. The valve cap is installed onto the end of the valve stem, furnishing a second
airtight seal. The cap also protects the threads on the end of the stem and keeps dirt and moisture out of
the valve body. The screwdriver type cap (NSN 2640-00-060-3550) has a forked tip that may be used to
install or remove the valve core. The plain cap (NSN 2640-00-255-9346) is generally used on rubber
cover valves and has a skirt that contacts the rubber cover on the valve stem. Screwdriver and plain caps
are interchangeable. The plastic cap (NSN 2640-01-098-2029) is used on all vehicles that service aircraft
or are dispatched on flight lines. Each of these caps should be finger-tightened only.