AIR APPARENT
MARK PUTZ
ASSOCIATE EDITOR
If tires indeed represent the second-largest expense for truck fleets, and if more than 80% of tire problems are caused by improper inflation, the concept of automatic inflation systems might just begin to make sense to cost-conscious carriers.
Trailer tires lose air pressure whether the trailer is moving or just parked in a corner of the yard. An under-inflated tire not only impacts its durability, but also affects its rolling resistance, which means a loss of fuel economy. And that means cost-per-mile figures go skyward.
According to Goodyear Tire & Rubber, a 10-psi drop in a truck's tire pressure will increase rolling resistance by 2%. Tires that are under-inflated by 15% will cause fuel penalties of around 2.5%. Cost-per-mile penalties like these can add up to big bucks, and have some fleets opting for automatic tire inflation systems.
The ArvinMeritor Tire Inflation System by Pressure Systems International (PSI), San Antonio, Texas, keeps tires properly inflated by using compressed air from the trailer air system to inflate any tire that falls below a pre-set pressure.
While on the road, the system automatically keeps all trailer tires inflated to the pressure the driver has dialed into a control box.
Called an automatic tire inflation system (ATIS), it connects all tires on the trailer to a controlled air supply to fill and maintain air pressure at a constant and proper level — even when the vehicle is moving. As air pressure decreases from the tire manufacturer's recommended level, the system automatically routes air supply to a control box and then into the axle. The air is then distributed to each tire. The ArvinMeritor inflation system is self-contained on the trailer so it can adapt to any tractor.
A PSI spokesman said the 9-year-old company has sold more than 400,000 trailer systems in the United States, not including sales to the U.S. Army. He said the PSI inflation systems are also being sold in Europe and Southeast Asia.
Cycloid Co., Cranberry Township, Pa., offers an air compressor system (ACS) that is self-contained, providing continuous tire pressurization while a truck is moving. At the heart of ACS is an inertia compressor mounted at the center of the wheel that uses its rotation to power the pump and maintain constant tire air pressure.
A compression stoke occurs with each wheel rotation. Atmospheric air is compressed up to the preset pump pressure and passed through a set of check valves, then through tire valves — one for each tire. These valves protect one tire if the other fails. The pump continuously operates while the wheel is rotating. When a tire's pressure drops below the pump maintenance pressure, compressed air flows through the valves and replaces the lost volume.
Since the pump operates only while the wheel is rotating, maintenance pressure is set at the expected tire operating pressure (about 10% above the desired cold pressure). Once the tires stop rotating and cool down, their pressure will return to the desired cold pressure. The pump continuously operates as a "trickle charger" for tires, keeping them at their proper pressure.
Also available is the PressureGuard Automatic Tire Maintenance System from Innovative Transportation Products Inc. (ITP). The Dallas, Texas-based firm says its tire inflation system routes air from the trailer's supply tank through the axle to the hub, and then to the tires, so they maintain pressure at a preset level. As a result, the company says, tires last longer, wear more evenly and yield higher quality casings for retreads.
ITP said its system can produce a savings of $552 a year per trailer and reduce a fleet's tire-related downtime by more than $400 a year per trailer, (based on a trailer traveling 92,000 miles a year). The company figures the cost of one blowout per trailer per year at $420, factoring in the cost of a new tire, roadside service call and loss of two hours of road time.
Most automatic inflation systems eliminate the labor cost of manual inflation and reduce the likelihood of catastrophic puncture damage. The systems support a continuous air demand in the event of a puncture to maintain tire pressure. Usually, the system triggers a warning light visible to the driver. The system then acts as a safety aid — keeping the tire inflated sufficiently to minimize the risks of tire damage or destruction.
This "run flat" capability was part of the original design of the Central Tire Inflation System (CTIS) from CM Automotive Systems Inc., Walnut, Calif.
Air can be continuously supplied to a flat tire from the system, allowing a trailer to limp home on a tire that might otherwise come off the wheel rim. The system features a controller panel with a digit LED display for pressure readout. The controller is a digital electronic circuit that controls the total process of pressure adjustment. It can be mounted on the dash panel to provide the driver easy access to the control switches. The power manifold is a cluster of solenoid valves, one each for inflation, deflation and quick exhaust for rapid pressure drop. It can be mounted inside or outside the cab because of its watertight construction.
The interconnecting wire harness provides the communication between the controller and the power manifold. The wheel valves provide a controlled passage for air to go in and out of the tires and isolate each tire at the end of the pressure adjustment cycle. The wheel valves have no electrical connections and are operated by the available air pressure regulated by the power manifold through hoses. Tires can also be inflated manually, independent of the CTIS, with valves readily accessible to the operator.
Industry officials say automatic inflation systems cut operating expenses by running proper tire pressure on every trailer wheel — 100% of the time.
And even the best driver in your fleet can't boast that.
