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Tires
Mismatching

Equipment Operator Basic - Beginning construction equipment operators manual
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Figure  3-12.—Valve cores. UNDERINFLATED.— An underinflated tire is shown in figure 3-11, view B. This tire does not contain enough air for its size and the load it must carry. It flexes excessively in all directions and gets hot. In time, the heat weakens the cords in the tire, and it blows out. Underinflation also causes tread edges to scuff the road that puts uneven wear on the tread and shortens tire life. Never run a tire flat, or nearly flat, unless the tactical situation in combat requires it. When run flat for even a short distance or almost flat for a long distance, the tire may be ruined beyond repair. OVERINFLATED.—   An  overinflated  tire  is shown in figure 3-11, view C. Too much air pressure also causes tire failure. Excessive pressure prevents the tire from flexing enough and causes it to be constantly subjected to hard jolts. When an overinflated tire hits a stone or rut, the cords may snap and cause a break in the cord body. The center of the tread wears more rapidly and does not permit equal wear across the entire tread. Hard riding from too much air pressure also increases wear and tear on the vehicle. Valves For  speed  and  convenience  during  inflation,  valve stems should be readily accessible. They should be properly centered in the valve holes and slots to prevent scraping against the brake drums. They should be placed so the valves extend through the wheels. Valves on the inside duals should point away from the vehicle, and the valves on the outside duals should point toward the vehicle. On dual wheels, the valve of the outside dual is placed 180 degrees from the inside valve for speed and convenience  in  checking  pressures  and  inflation.  With this arrangement, the locations of the valves are always known even when you are checking them in the dark. Spare tires should be mounted so that the valve is accessible for checking and inflating. VALVE CORES.—  The valve core (fig. 3-12) is that part of the valve that is screwed into the valve stem and permits air, under pressure, to enter, but prevents it from escaping. Two types of valve cores and two sizes of each type are in use today. The two types are the visible spring type and the concealed spring type. The two types 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 seat inside the stem. Directly below the shell is a cup that contains a rubber seat, which,  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 (fig. 3-13) is also a component part of the valve and is screwed onto the end of the stem, providing a second airtight seal. The cap also protects the threads on the end of the stem and Figure  3-13.—Valve  caps. 3 -8







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