The valve stem is probably the one component in the tire and wheel assembly that is most taken for granted and least thought about.
Like Rodney Dangerfield, it "don't get no respect" or at least not much despite the fact it performs the vital function of enabling inflation pressure to be added to the tire and then seals it in. When valve stems fail to seal or leak, you have a problem.
Commercial tire dealers have to stock a lot of different valves to service all different customers.
Be sure always to buy quality valve stems from a reputable supplier. The Tire & Rim Association (T&RA) and the Society of Automotive Engineers (SAE) have established standards for design and performance requirements for aging and ozone resistance.
Good valve stems should be marked with the TR (Tire & Rim) number, the manufacturer's name or trademark, part number and country of origin. Not all manufacturers will put all of this information on the valve stem, but the more information you have, the more reputable the manufacturer is and will stand behind its quality product.
In the last several years, cheap, off-shore valves have been coming into North America. The quality of these valve stems varies from one manufacturer to another and from one shipment to another.
There may not be markings on these valve stems, so if a problem does arise with them, it is difficult to impossible to go back to the manufacturer. If the price is too good to be true, run away.
There are several components to the valve stem assembly: the valve stem, grommet or O-ring, valve core and valve cap. Each performs a vital function in ensuring that tires are properly inflated for thousands of miles. If any one of these fails or goes missing, the tire is in jeopardy.
Let's look at each.
Most tire valve stems are made of brass since brass is corrosion resistant, can be alloyed for ease of machining and can be bent easily to facilitate servicing.
Rubber also adheres to brass fairly easily, a trait that is necessary especially for high-pressure valves used in truck tires, which need good rubber grommet-to-metal adhesion to keep the grommet attached to the valve.
The most common valve stems for steel wheels used in heavy-duty truck applications, which usually have a 0.625-inch valve hole, are the TR500, TR501 or TR570 Series clamp-in style valves.