Fisher: Valve

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.

However, trucks are being imported with steel wheels that have 9.7 mm (0.382-inch) valve holes and require "MS" Series valves, which have black O-rings and are similar to the TR540 Series valves.

The O-rings should be heat resistant as well. Silicone O-rings can be red or black. Red O-rings are designed for high-temperature applications.

Valve stems used in aluminum wheels must be plated so that they will not corrode the aluminum. There are several different types of truck valve stems for aluminum wheels depending on wheel type.

Aluminum wheels with 9.7 mm (0.382-inch) valve holes use O-ring seal type TR540 Series and grommet seal type TR550 Series valve stems.

The rim thickness required for these valves is 0.218- to 0.330-inch. Aluminum wheels with valve holes that are 0.625-inch use TR509 through TR511 valves. European 335mm bolt circle wheels use MS Series valves.

High-heat-resistant grommets should also be used since the tire and wheel assemblies are so close to the brakes.

The temperature range for most truck valve grommets is -40°F (-40°C) to 250°F (121° C), but there are also grommets available that are rated at 400°F (204°C) and should be used in applications where excessive heat is generated, such as in sanitation operations.

Grommets can be red or black, but not all red grommets are heat-resistant, so it is wise to check with your valve supplier to ensure you are getting heat-resistant grommets.

The valve core is a critical component within the valve stem. It opens and closes the valve and allows the inflation pressure in the tire/wheel assembly to be adjusted. If there is no valve cap on the valve stem, dirt, ice, debris, etc. will prevent it from sealing properly.

It also is exposed to heat, so special high-temperature cores are available for applications where excessive heat is generated. These valve cores usually have a red seal indicating a temperature range of -40°F (-40°C) to 280°F (121°C) and are designed for medium and heavy-duty truck applications.

Filter valve cores that prevent debris from entering the valve sealing area are required for use in tire/wheel assemblies that have some aftermarket materials installed inside, such as balancing granules/powders.

Special valve cores with low crack pressures are used in the hoses of automatic tire-inflation systems (ATIS). Each brand of ATIS may be different and require a specific crack-pressure valve.

If you have to replace an ATIS valve core, check with your fleet customer to determine which core to use. Never replace the special valve core at the end of the hose where it connects at the hub with a standard valve core.

Central tire-inflation systems (CTIS) that inflate and deflate tires on demand do not use valve cores in the hoses or in the valve stems.

The proper procedures must be followed when installing a valve stem. On aluminum wheels a non-water based tire lubricant or a dielectric grease should be used on the valve-stem threads, grommets or O-rings prior to installing the valve. (Do not use anti-seize type compounds.) This prevents corrosion from growing around the O-ring or grommet, which squeezes it and causes leaks.

Care should be taken when installing the valve stem so that the O-ring is not nicked or damaged, as this will cause a leak as well.

All truck tire valves must be installed with the proper torque. TR500, TR501 and TR570 Series valves should be torqued to 35 to 55 in.-lbs. "MS" Series should be torqued to 106 to 133 in.-lbs.

TR 540 and TR550 Series should be torqued to 80 to 125 in.-lbs. TR509 through TR511 should be torqued to 100 to 125 in.-lbs.

The only way to know you have tightened valve stems properly is to use a valve-stem torque wrench, available from any reputable tool supplier.

Valve cores must be installed properly as well. Over torquing valve cores can damage the valve cores and valve-core seats, which will cause leaks. Cores should be tightened to 2 to 5 in.-lbs. of torque, which is essentially hand tight.

To be precise, find torque wrenches for valve cores from tool suppliers also. Always store valve cores in a box and not loose in a dirty shop environment. They must be kept clean to ensure an air-tight seal is achieved when installed in a valve stem.

Valve caps provide the final seal to the valve stem and prevent contamination of the valve core. They keep dirt and debris out of the valve and maintain inflation pressure if the valve core leaks.

It's a pretty important job considering how many tire and wheel assemblies are running around right now without valve caps.

There are two types of valve caps: sealing and non-sealing. Non-sealing valve caps are usually plastic and may come with new valve stems to keep dirt out of them. Medium and heavy-duty truck tire valves require a metal, sealing, high-temperature valve cap.

Inflate-through valve caps are designed for high-pressure truck tire service and act as an inflate-through extension as well. They provide two seals and allow tires to be gauged and pressures to be adjusted without removing the valve cap, which saves about 65% of the time when checking tire pressures.

They operate like a check valve and become tighter as inflation pressure is added. Inflate-through valve caps should never be used as a replacement for valve cores.

The internal seal in these valve caps can be distorted if they are over torqued so they should be installed hand tight. Pliers should never be used to install them.

Like any other component, valve stems require maintenance. Valve stems should be inspected every time a tire is balanced or the pressure is checked.

Check to see that a valve cap is installed, and look for bent stems and damaged threads. If the valve cap is missing, ensure the valve stem is free of debris.

If the threads of a valve stem are damaged and a valve cap cannot be installed or the threads on the inside of the valve stem will not allow the valve core to be properly installed, the valve stem should be repaired. A valve repair tool can extract damaged cores, rethread inside the stem and rethread the outer part of the stem as well.

Valve stems should be inspected every time a tire is changed. It is not necessary to change the valve stem at every tire change but it is necessary to install a new valve core.

Grommets should be inspected and replaced as needed. If the valve stem requires replacement, always check the rim valve hole for nicks, burrs and corrosion and lightly smooth out the surface to remove them.

On aluminum wheels, if the valve-hole seating surface is severely pitted, remove the wheel from service.

You see there are a lot of things to like and respect about valve stems, but you have to treat them right and give them some attention. You can't treat them like Rodney Dangerfield.

To put a smile on your face today, I'll share with you one of my favorite Rodney Dangerfield one liners: "Even when I was a kid, I got no respect. I could tell that my parents hated me. My bath toys were a toaster and a radio."

Peggy can be reached via e-mail at [email protected] Her previous columns are available at www.tirebusiness.com.

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