Issue link: https://read.dmtmag.com/i/34500
AIR INFLATION AND PRESSURE MONITORING SYSTEMS Proper inflation pressure is critical to the overall Some systems provide inflation pressure performance of all tires on the road today. Today’s radial truck tires will lose less than one psi per month due to air migration through the casing. Faster loss of inflation can only occur in conjunction with some sort of leak in the wheel, valve stem, or tire structure. Whatever the source of the leak, it must be identified and corrected to avoid further damage to that component, possibly leading to a compromise in safety. AVAILABLE SYSTEMS Tire pressure monitoring systems have been legislated for all vehicles by the TREAD Act (Transportation Recall Enhancement, Accountability, and Documentation). The implementation schedule is in place for vehicles with gross vehicle weight (GVW) below 10,000 lbs, but is yet to be determined for heavier vehicles. The existing systems “read” the pressure in the tire via a sensor mounted on the valve stem, wheel, or inside the tire. Sensors that are not physically inside the tire/wheel cavity cannot accurately measure the internal air temperature, so are they unable to determine the “cold inflation pressure.” In addition, external sensors may require additional air line plumbing that creates additional potential leak points. Monitoring systems may provide either pressure data or a low pressure warning. The pressure data may be “hot” or “cold” pressure, so it is necessary that the person viewing that data fully understands which pressure is reported and what it means. Low pressure alarm systems only alert the driver when the pressure in a particular tire (or pair of dual tires if linked together) is below some fleet-chosen minimum. This value may be preset by the sensor supplier or may be programmable by the fleet. Tire manufacturers, through the Rubber Manufacturers Association (RMA), have agreed that a tire must be considered flat if the inflation pressure is 20% or more below the pressure recommended for that tire. A flat tire must be removed from the rim, thoroughly examined, and properly repaired prior to re-inflation and use. information at the sensor site only, so the driver must walk around the vehicle to gather/view either the pressure reading or low pressure warning. Other systems transmit the information to the cab where it may be viewed by the driver, and/or sent to a central facility if the vehicle is tracked by satellite Inflation-only systems are designed to add air to maintain a preset pressure but do not have the ability to reduce the pressure should a tire be over inflated. These systems can account for slower leaks (determined by the air delivery capacity of the system) and provide some warning to the driver when the system is energized (adding air) or when it cannot keep up with the leak. Almost all inflation- only systems use air from the vehicle air brake system, so they will be limited in max pressure and available volumetric flow. In addition, these systems are usually only applied to trailer axles where plumbing the air supply line is easier. Tire inflation systems may add air to tires determined to be below some fleet chosen pressure. Some Central Tire Inflation (CTI) systems will also allow pressure reduction on any tire on the vehicle to maintain some given pressure level. Such systems are rather expensive and more often used only on specialty vehicles (Military, emergency response, National parks, etc.) A key factor in any monitoring or inflation system is determining whether the target or set pressure is a “hot” pressure or a “cold” one. This should be discussed with your tire manufacturer’s representative. Air inflation systems are not guarantees against low pressure situations. All vehicles should still be subject to pre-trip inspections, and systems operation should be verified routinely. Truck Technical Specifications 19