ROCHESTER HILLS, Mich. (June 19, 2001)—Like Rodney Dangerfield, the lowly tire valve stem just doesn't seem to get any respect. It's a piece of hardware that is usually taken for granted and readily forgotten.
People try to find the cheapest ones they can buy because, after all, it's not like they're really doing anything other than providing a channel through which tires are inflated and deflated and keeping the air in the tire. But isn't that an important job? If the valve stem leaks, you've really got a problem.
For the last two to three years, offshore valves have been coming into the U.S. for as little as 15 cents in the case of a standard 572 truck tire valve stem. (Fleets pay 40-70 cents each for these.) The rate at which they are now being imported is escalating—and the quality of these valves is all over the place, with the vast majority being in the dumper.
Good-quality, American-manufactured valve stems adhere to an SAE (Society of Automotive Engineers) standard that sets performance requirements for aging and ozone resistance. Many offshore valves do not meet those standards. They also can vary in quality from shipment to shipment and come with no product liability insurance. They may last only three months before starting to leak. Because there is no name or marking on these valves stems, there is no traceability and nowhere to turn to should a problem arise.
So how do you select the right, high-quality valve stem for your customers' tires?
First of all, make certain your tire valve supplier is knowledgeable about the product he or she sells. Be aware of the quality parameters tire valves and tire valve manufacturers should meet. Ask questions about the valve stem's expected life, how often it should be changed, what makes it better than other manufacturers' valve stems etc.
Look for the TR (Tire and Rim) number on the valve stem. This is essentially a part number assigned by the Tire and Rim Association. Although the existence of a number does not guarantee a certain level of quality, the manufacturer should be making valves in accordance with SAE material standards and Tire and Rim dimensions. Also look for the manufacturer's name or trademark, part number and country of origin.
Not all manufacturers put such information on the valve stem. However, the more information you see, the better informed and sure you are that the manufacturer is reputable, produces a quality product and will stand behind it. At least you'll know who to contact if there is a problem with the valve stem.
Some valve manufacturers also put their mold number on the valve stem. This is good to have to troubleshoot a problem should one arise.
Next, be sure you select the right valve stem. Very different valve stems have a nasty habit of looking a lot alike. Make sure the valve stems you select for your truck tire users are high-pressure valves that can handle pressures up to 155 psi. Passenger valve stems only go up to the 65 psi.
Truck valves come in two basic dimensions: the .625-inch rim hole width for steel wheels and the 9.7 mm rim hole for aluminum wheels. Most tire valves are brass, since brass is corrosion resistant and can be alloyed for ease of machining and can easily be bent to facilitate servicing. As you know from your tire cord knowledge, brass adheres to rubber fairly easily and high-pressure valves also need good rubber to metal adhesion to keep the grommet attached to the valve.
The TR570 series clamp-in style valves are commonly used in heavy-duty truck applications. These valves can be bent to provide needed clearance away from the brake drum. Make sure you use the proper equipment to bend them or you can purchase them already bent.
Since heat can be an issue due to the proximity of the brakes, make sure you use grommets with high heat resistance. Some people think that red grommets are better than black grommets for this application, but not all red grommets are heat resistant although the price for them is double that of heat resistant black grommets.
In aluminum wheels, mostly 9.7 mm tire valves are used—but these valves must be plated. Alcoa recommends that a little Freylube be used around the valve stem hole to prevent corrosion from growing around the grommet, which squeezes it and causes leaks. Take care when installing these stems. They use an O-ring instead of a grommet. If the O-ring gets nicked or damaged during installation, the valve stem will leak.
Many aluminum wheel users utilize metal truck valve extensions that make the valve stem more accessible. In that case, it is imperative that an extension stabilizer be employed to prevent valve stem breakage and loosening of the valve stem nut due to vibration.
The valve core is a critical and hard working component of the valve stem.
It is the paramount seal of the valve assembly and is exposed to heat. If there is no valve cap on the valve stem, it is also exposed to ice and dirt. It must perform in a wide range of temperatures and pressures and still seal the air channel. When selecting valve cores, always spec for high temperature.
The type of service for which the valve core is made is indicated by the seal color on the core. A red seal indicates high temperature use, a blue seal is for air conditioning, and a core with a green seal is to be used with hydro-fluorides.
Valve cores must be clean in order to ensure an air-tight seal, so store them in a box rather than loose in a dirt-prone environment. Installing them too tight in a valve stem will damage the core and also create a problem. They should be tightened to between 1.5- and 3-inch pounds of torque. In case you don't have a “Barbie”-sized torque wrench, this equates to hand tight. (Snap-On Tool Corp. does make a tool, though, that measures inch pounds if you feel the need to add one to your tool collection.)
Tire valve caps provide the final seal to the valve stem assembly and prevent contamination of the valve core. Not all caps are created equal and you should be aware of the differences.
First, there are sealing vs. non-sealing valve caps. Black plastic caps are non-sealing and should not be used once the valve stem is installed in a tire/wheel assembly. Metal valve caps provide a good quality seal, and high heat resistance can be specified as well.
Gaining in popularity are double seal or inflate-through valve caps that provide two seals. They allow the use of inflation gauges and chucks without removing the cap. This saves an enormous amount of time (about 65 percent) when doing fleet surveys and yard checks.
However, it's important to know that these valve caps can be over-torqued—which will distort the internal seal in the cap. Inflate-through valve caps should be installed hand tight.
Never use pliers to install them. (I have heard of some people installing these caps extremely tight with pliers to prevent theft. It would be better to use Lock-Tite than risk damaging the valve cap.)
Valve stem manufacturers recommend that valve stems be replaced every time a tire is replaced and that valve stems be inspected every time a tire is balanced or the pressure is checked.
Make sure the valve core is free of debris and always make sure a valve cap is used. When installing a valve always check the rim hole for nicks, burrs or corrosion.
Valve stems commonly used in medium truck tires such as the TR570 series valves should be torqued to 30-45 inch pounds. Valve manufacturers recommend that valve torque be checked just like wheel nuts. And remember: After you install a valve, retighten it 24 hours later.
As you can see, there is a little more to valve stems, cores and caps than meets the eye.
It makes good sense to install good quality air retention hardware, especially if you are mounting premium truck tires on the rims or wheels. Don't be penny wise and pound-foolish. If you are selling your fleet account high-quality tires and retreads, treat your tire valve hardware with the same importance.
Don't risk jeopardizing the health of these tires for a few cents saved on valve stems, cores and caps.
Ms. Fisher is president of Fleet Tire Consulting in Rochester Hills, Mich.