If your fleet is like most, tires are your No. 1 maintenance expense. And it’s common knowledge that keeping them properly inflated will greatly prolong their life.
But, far worse than a tire meeting an early demise is a wheel assembly coming off on the road. This happens hundreds of times a year, says the National Transportation Safety Board. In many cases, the culprit is a damaged, overloaded or misadjusted wheel bearing. The assembly can become hot enough to seize and snap a spindle off, and the wheel and tire are free to cut a swath of destruction.
The good news? At least for trailers, there soon will be a way to warn drivers of excessive wheel-end temperatures, while ensuring that tires stay properly inflated. This capability will be found in the ArvinMeritor/Pressure Systems International Tire Inflation System later this year.
The existing system uses air from the trailer’s supply line and routes it to a weatherproof control box, then shunts it via flexible air lines to drilled, tapped, plugged and pressurized axle tubes. The air then moves to the tires, when needed, through a rotary union in the spindle end of the axles. A dynamic seal, with only one moving part, allows rotation. In turn, each rotary valve is connected to the tires on a dual assembly via two braided hoses with check valves.
While on the road, the system automatically keeps all trailer tires inflated to the pressure dialed into the control box. Inflation triggers a warning light (typically, installed on the trailer’s left front corner within sight of the tractor’s left rearview mirror). In the event that a leak’s simply too big to handle, a check valve will isolate the tire.
Fleet guys I’ve talked to like the system, and have reported 30 to 50 percent reductions in total tire costs. With this latest, temperature-sensing enhancement, they’ll have reason to like it even more. Here’s how it works:
The plug used to cap the pressurized axle tube has an extra hole, which is sealed with a eutectic alloy plug. When bearing-threatening temperatures are reached, the alloy melts, the extra hole opens, and air is dumped rapidly from the axle. The air flow is sensed at the control box, which lights a blue light, again at the front left corner of the trailer. To help pinpoint the problem, the escaping air makes a loud, shrieking noise at the affected wheel end.
At that point, of course, the vehicle should not be operated until the problem is corrected. That may mean some downtime, but – when you consider the alternative – it’s time well spent.
