ROCHESTER HILLS, Mich. (Aug. 1, 2005) — Air. It's the gift of life. While that's true for people, it's also true for tires.
You know this as well as anybody. It's the air that carries the load, not the tire. Flat tires don't carry diddly.
You've seen proof of this time and time again, I'm sure. How many tire sidewalls have you demounted from truck wheels with the crown area long gone?
Air. It's something we all take for granted, even in our tires.
Some truck fleets are beginning to take air seriously and are spec'ing their trailers with tire inflation systems since they readily acknowledge they need help in getting the air actually into their tires. Despite some fleets' best efforts, there seems to have been a short between the air hose and the tire. They just couldn't seem to make the connection. So technology has come to the rescue.
Why should you care? Well, the tires you sell these fleets should wear much longer and their casings should be better candidates for retreading since they were kept from running underinflated. Also, you may be faced with servicing the tires on these vehicles equipped with tire inflation systems, and it might be helpful if you knew what you were doing. (Although I've had many guys argue that point with me.)
Tire inflation systems take the air that is stored in the vehicle's air brake tanks and uses it to supply air to the tires. This can be done on demand or automatically triggered through sensors that monitor tire pressure.
Two types of systems
Tire inflation systems can be broken down into two types: automatic and variable. Automatic systems maintain tire pressure at a single preset level. They allow a vehicle to remain in-service despite small air leaks in one or more tires. Usually a warning lamp on the trailer nose indicates to the driver when a tire or system service is required.
Automatic tire inflation systems have no operational involvement from the driver. They automatically sense the pressure in the tires and inflate as necessary when the tires lose air.
Variable tire inflation systems can raise or lower tire pressures during vehicle operation to compensate for varying load and road conditions, in addition to maintaining tire pressure. These systems allow the driver to interact with the system and change tire pressure on demand. They are much more complicated and expensive than automatic systems and are usually used for specialized on-off road operations such as logging, construction, mining, gravel hauling, concrete, exploration and military.
More and more commercial truck fleets, however, are putting automatic tire inflation systems on their over-the-road trailers. These systems use compressed air from the vehicle's air system and transfer this air to a frame- mounted control unit. Air is then delivered through the axle to a wheel end rotary union that distributes the air to the tire valve stems.
These inflation systems must be vented to prevent wheel end failure that may result from hub pressurization in the event of component failure.
In automatic tire inflation systems, each tire is connected to the air source, so one tire never supplies air to another. The system directly senses the pressure in each tire and adds air to the appropriate tire when necessary.
Since the air is being taken from the vehicle's brake system, a pressure protection valve is used to ensure a rapid loss of tire pressure will not drain the vehicle air system below a safe pressure required for proper braking. If a significant loss of air should occur in a tire or the inflation system itself, the remaining tires are protected from air loss by check valves in the air hoses.
While this system sounds great from a tire inflation maintenance standpoint, it doesn't eliminate tire maintenance responsibilities. It still is necessary to check whether the system is functioning correctly, if tires have leaks or other out-of-service conditions and to measure tread depth.
While tires with small punctures can remain in service indefinitely— since the inflation pressure is maintained by the system—it is possible that air eventually will migrate through the belts or cords of the tire and cause a separation at or near the puncture. Therefore, tires found with leaks and penetrating objects should be removed and repaired as soon as they are found.
There are about six or seven companies that make tire inflation systems. Most of them make systems only for trailers since it is much easier to run the plumbing for these assemblies through a hollow trailer axle than a drive axle on a truck or tractor that has no room inside for today's pressure system devices.
Power units require exterior plumbing that is costly and vulnerable to damage and aren't suitable for all applications, vocations and climates. As a result, introduction of tire inflation systems for trucks and tractors has been slow.
Trailers, however, are a different story. They have been the focus since the beginning of tire inflation system development because their tires get checked less frequently than tractors.
Central tire inflation systems have been around for more than 10 years, but they are really beginning to catch on in the last couple of years. There are several reasons for this.
Fleets have found that their biggest savings come from reduced road service calls. Those fleets that deliver just-in-time freight can't afford to have enroute delays. Obviously, enroute flat tires are usually avoided due to the air pressure that is provided to tires that have punctures.
The cost of one road call can pay for a tandem axle, trailer tire inflation system that can run between $620 and $800. Some fleets also have reported that their tread wear has increased dramatically.
Maverick Transportation Inc., which runs a truckload flatbed operation, has increased its tire mileage by 1,000 miles per each 32nd inch of tread wear since using these systems on their trailers over the last five years, according to the company.
Fleets using this equipment also have reported improved retreadability and a reduction in scrap tires. This translates into lower tire costs per mile. Fleets that don't have the opportunity to maintain their trailer tires because the trailers don't return to a terminal regularly find these systems protect the tires while they're off site.
Further, many of the fleets that are spec'ing the new wide base tires on their trailers also are spec'ing trailers with tire inflation systems as a hedge against being shut down on the side of the road if one of these tires goes flat.
OK, so what do you do when you're faced with servicing the tires on a trailer equipped with a tire inflation system?
First check the pressure system light normally located on the nose of the trailer on the driver's side. If it is off, then the pressure in the tires is fine.
But you still should inspect the tires for unserviceable conditions like cuts, exposed steel, separations, low tread depth, etc. In any case, a lot of tire pressure gauge time has been saved for you.
If the light is on, then there's a problem. It is probably a tire that is damaged and is causing the system to lose air. Unfortunately, you have to check all the tires on the trailer until you find the one that is low on air.
To do this, remove the hose end at the connection on the hubcap. Press the tire pressure gauge to the hose end. If the pressure is correct, reconnect the hose end, firmly hand-tighten and then check the pressure in the other tires in the same manner until you find the low tire.
If the pressure in all the tires is correct, then there is probably a leak in the system. Advise the fleet maintenance personnel about the problem.
When removing tires for replacement or repair, remove the hoses from the tire valve stems. Carefully remove the tire(s) so that you don't abrade or break the hoses that are still attached to the hub connection, while sliding the tire and wheel assembly over the axle end.
When re-installing tire and wheel assemblies, take care in placing them on the axle end so that the hoses still attached to the hub are not damaged. Be sure the inner and outer valve stems are 180 degrees apart.
As you can see, air is not only a lifesaver, but in the case of tire inflation systems, a tread saver, casing saver, road-call cost saver and a time saver for both the fleet and you.