Make the Right Turn
Don’t Underestimate the Impact of Proper Valve Stem Torque
When the ITRA’s Commercial Tire Service Program began in 1996, I thought I knew everything about truck tires and wheels. Years of experience on the road and in the shop made me an expert as far as I was concerned. I didn’t think I would learn anything new. I knew the right way to service tires, so putting together a training program would be a piece of cake.
As I began gathering material from various sources, the amount of readily available information was amazing. Surprisingly, though, I was seeing most of the service manuals and materials for the first time, some of which had been available since the 1980s.
You don’t really know the rules until you sit down and read them. With that fact in mind, I spent the first few months reading and re-reading everything I could.
To this day, the shelves in my office remain jammed with manuals, bulletins and other technical literature I’ve collected over the years. And I continue to read a number of industry publications looking for new technologies and developments that may impact commercial tire service technicians.
Usually, any new technical or regulatory information means more work for the commercial tire service technician. And it’s no different whether you’re talking about the proper way to mount tire/wheel assemblies on commercial trucks, or dealing with the right way to secure wheel valve stems.
No Trivial Matter
Proper wheel torquing takes a serious investment in time and equipment, but the consequences of failing to install commercial tire/wheel assemblies correctly can be deadly. Regardless of the investment, most shops recognize the importance of safety cages and inflation devices because the risks to life and limb are obvious. When safety is the primary goal, teaching service technicians about subjects like wheel torquing is easy.
But what happens when you come across rules that appear to be so trivial? Sometimes the service technician may simply overlook them, continuing to do his job in the same fashion as in the past. Other times, the service technician may not have been instructed properly and doesn’t know or understand that he should do things a certain way.
In the eyes of the courts, no rule or regulation – or even accepted practice – is trivial, so it’s best not to ignore them. If the tire or wheel manufacturer requires valve stems be installed with a certain amount of torque, technicians must torque the nuts on the valve stems to the prescribed amount. Failure to follow even the smallest rule can have major consequences.
Do Technicians Really Know?
ITRA-certified Commercial Tire Service Technicians know the rules better than most, so they recognize the fact that following the rules word-for-word takes substantially more effort and time. Using a torque wrench to install wheel fasteners is the preferred method because of the torque/clamping force relationship. After all, none of us want wheels to come off moving vehicles.
But do commercial tire service technicians know they are required to use a torque wrench to tighten valve stems – and a different torque wrench, at that? After all the training efforts we’ve undertaken, we hope they all do. But let’s review it one more time.
Inches vs. Feet
The recommended torque for standard tubeless truck tire valve stems in a steel wheel is 35 to 55 inch pounds (in/lbs), according to the Tire and Rim Association’s 2000 Yearbook. An inch-pound is similar to the foot-pound measure used for torquing wheel fasteners in the sense that the formula is still Weight X Length of Lever.
However, while we can achieve 400 ft/lbs of torque on a wheel nut by applying 200 pounds of weight to a two-foot-long breaker bar, it will only take one pound of weight on a 35-inch lever to achieve 35 in/lbs of torque on a valve stem nut.
Armed with all this valuable information, I decided to conduct a non-scientific test to see what it takes to reach 35 to 55 in/lbs when tightening down a valve stem. I went to the local tool store to purchase a beam torque wrench and an open end wrench adapter. The model I chose had a working range of 0 to 500 in/lbs and cost less than $50.
I then took my new tools and proceeded to check the torque of a previously installed valve stem.
Much to my amazement, the valve stem was under-torqued. I estimate the actual torque was around 20 in/lbs because the nut moved with little effort and the wrench needle never made it half way between 0 and 50 in/lbs.
As soon as the wrench showed the torque was just below 50 in/lbs, I stopped applying force. And gave the valve stem a little wiggle. It was definitely tighter than most valve stems I’ve installed.
Being a true non-scientist, I decided to install a new valve stem using my new torque wrench to see if there was a real difference. I started the process with a standard open-end wrench, stopping as soon as I felt substantial resistance. At that point I used the torque wrench to finish the job. Again, the valve stem was tighter than most I’ve ever installed or seen.
Caution on Aluminum Wheels
Since wheel fasteners require retorquing after the first 50-100 miles of service to compensate for any joint settling, I decided to see if the same were true for valve stems. Approximately four hours after installing the new valve stem, there was no noticeable change.
On the other hand, aluminum wheel valve stems present definite problems when they are improperly torqued. If the valve stem is loose, the assembly leaks. If it is too tight, corrosion will begin to form around the valve stem and a leak will soon follow. The recommended torque for standard aluminum wheel valve stems is 7 to 11 ft/lbs or 80 to 125 in/lbs.
Limit Your Liability
Do commercial tire dealers need to run out and buy torque wrenches in order to install valve stems? In the eyes of a jury, a tire failure caused by an improperly torqued valve stem nut will result in substantial liability for the dealer if a torque wrench was not used. Your desire to be held liable in the event of a problem should be a sufficient answer.
But having a valve stem-specific torque wrench is one thing; making sure the technicians use them every time is another.
I don’t enjoy finding little rules and regs that make life harder on commercial tire service technicians. The fact is, however, the commercial tire service industry can take important steps to reduce liability by training technicians to know and follow all the rules – no matter how seemingly trivial – and providing the equipment necessary to meet the requirements of those rules.
Valve stems are no different.
Kevin Rohlwing is director of training for the International Tire & Rubber Association (ITRA), and this article originally appeared in ITRA’s Commercial Tire Service publication.