Freight-hauling equipment, trucks, tractors and trailers, continue to evolve as do the systems used to maintain tire inflation pressure such as tire pressure monitoring systems (TPMS), automatic tire inflation systems (ATIS) and central tire inflation/deflation systems (CTIS) and centrifugal force pumps. They have certainly come a long way from the first dual tire-pressure equalizers that appeared on the market in the mid-1980s, although you still can find equalizers on both trucks and trailers from time to time.
The adoption of these systems is growing, especially since they have been integrated with telematics. In fact over 70% of new trailers being built now are equipped with ATIS at the factory and more and more fleets are opting to equip their power equipment, as well as their trailers, with TPMS.
This growth in inflation and monitoring systems usage affects everyone who services tires on these vehicles, especially since their use is relatively recent. Many fleets complain that their tire service providers don't know how to work with these systems and tire dealers complain that their customers don't tell them they have these systems on their equipment. The result is that the adoption of these technologies is hampered.
So perhaps now is the time to look at each of these systems and determine what technicians need to inspect, replace, adjust and maintain to keep them operational and functioning properly, especially since so many commercial tire dealers are doing more and more trailer and tire maintenance for their fleet accounts.
Let's start with dual tire-pressure equalizers. These are low-tech components that are designed to maintain the same pressure between two tires of a dual assembly and indicate the state of inflation pressure in the tires. By keeping the pressure in a set of dual tires the same, irregular wear caused by improper load distribution is reduced.
They accomplish this by allowing inflation pressure to transfer from one tire to another through hoses that are plumbed to a check valve mounted on the hub and attach to the valve stem of each dual tire. The check valve opens to allow air to flow between the tires but closes and shuts the air off in case of an instantaneous air loss, which prevents both tires from going flat. Should a slow leak occur, the valve isolates both tires after the pressure drops about 10 psi.
While equalizers do not provide actual inflation pressures, they do provide a visual go/no go indicator that advises if the tires are underinflated, overinflated or at the correct pressure. The operating pressure is set at the factory.
When servicing tires on vehicles with dual-tire equalizers, technicians must remove the hoses from the tire valve stems and carefully remove the tire/wheel assemblies from the axle end without damaging the hoses. Hoses should be inspected for damage and reattached to the tire valve stem. The tire pressure indicator should also be inspected to ensure it is intact and pressures should be checked to ensure the equalizer is still operating accurately.
Since there is no way to adjust the operating pressure, if the equalizer is not accurate, the customer should be advised of this situation and replace the equalizer.
Current TPMS use electronic sensors that monitor tire pressure and temperature. These sensors can be mounted on the wheel, on the innerliner or at the base of the valve stem inside the tire/wheel assembly or on the external end of the valve stem like a valve cap. They use radio frequency to transmit data to the system's receiver.
There are three types of TPMS. The first is basic TPMS, which delivers alerts to the driver on an in-cab display. The driver as well as the technician can see the current tire inflation pressure on the display when the ignition is turned on, which eliminates the need to manually check tire pressures. The technician can set the target pressure by using the in-cab display while adjusting tire pressure.
The second is TPMS Integrated with telematics, which alerts the fleet hundreds of miles away to any tire problems the vehicle is experiencing as well as the driver through the in-cab display. Data are transmitted off the vehicle using the cellular network to the cloud where they are analyzed and stored.
Reports and alerts are then sent via e-mail to the appropriate parties. Fleets can see the current status of their vehicles' tires through the internet. Changes in target pressure can be made over the internet for some systems while others required them to be made on the vehicle.
Both basic TPMS and TPMS Integrated with telematics have a receiver to collect the tire data. They may both also have an antenna or repeater, especially if they are monitoring trailer tires, too. You should check to see that these components are present and intact. Technicians should always check the in-cab display to obtain current tire pressures.
For vehicles without in-cab displays but communicate TPMS information through telematics providers, technicians should check with fleet maintenance/dispatch to verify tires are inflated properly.
The third type of TPMS is gate, lane or handheld readers, which provide interval monitoring of tire pressures and temperatures at static or low vehicle speeds. In-cab displays are usually not included with these systems since the data are taken at a fleet's location, transmitted to data storage devices or the cloud, and alerts are generated for service personnel at that location.
Instead of checking an in-cab display for tire pressure and temperature status, technicians use the computer monitor in the fleet's facility where tire status is displayed for gate and lane readers. Inflation pressures taken by handheld readers are usually displayed on the reader itself. If the gate, lane or handheld reader is not working, advise the fleet.
For all types of TPMS, if the display indicates that a tire problem exists, inspect the tire and inflate if that is appropriate. If the tire has less than 80% of its targeted pressure, it should be removed, demounted and inspected. If the display indicates a missing sensor, advise the fleet. It could be the sensor is missing or the sensor no longer works.
Perhaps the trickiest part of working with tires equipped with sensors is identifying the type of sensor that is being used. Obviously external sensors are easy to identify, remove and reinstall when servicing a tire/wheel assembly. When installing them, as the sensor is threaded onto the valve stem, a brief hiss of air escapes.
The sensor should then be tightened properly until no hiss of air is detected. They should be tightened to the manufacturer's specifications, however, if you don't know what they are, external sensors should be hand tightened plus an additional quarter turn.
Hopefully vehicles equipped with internal TPMS sensors have some markings that indicate the presence of a TPMS such as a sticker with the TPMS brand name on it, on the door or above the tires. If not, it might be a good idea to check with the fleet to ensure there is no TPMS on the vehicle before servicing its tires. If there is, find out what type of sensor the fleet is using.
For sensors that are mounted at the base of the valve stem, begin demounting the tire just past the valve stem and stop before your tire tools get around close to the valve stem again. For sensors that are strapped in the wheel well, they should be mounted 180° from the valve stem, so keep that location in mind and your tire tools away from this area when you demount and mount tires on these wheels.
Unless you know how to change the wheel positions of the sensors, make sure they are put back in the same positions from which you removed them.
Automatic tire inflation systems (ATIS) and central tire inflation/deflation systems (CTIS) inflate tires by drawing air from the vehicle's air brake system. These systems transfer compressed air from the vehicle's air system to a frame-mounted control unit. Air is then delivered to a wheel-end rotary union that distributes the air to the tire valve stems. All tire inflation systems must be vented to prevent hub pressurization in the event of a component failure.
Air is supplied directly to each tire. One tire never supplies air to another tire so the correct pressure is maintained in all tires. A pressure protection valve is required in these systems to ensure a rapid loss of tire pressure does not drain the vehicle air brake system. If a significant loss of air is experienced in a tire or in the system itself, the remaining tires are protected from air loss by check valves in the air hoses.
ATIS supply air to the tires automatically while CTIS do this on demand. CTIS are usually used by powered vehicles that go off-road, such as in logging, construction and military operations.
ATIS maintain a minimum tire pressure at a single preset level and are either electronically or pneumatically activated. Electronically activated systems use an electronic control unit (ECU) to measure tire pressures at regular intervals and inflate the tires as required.
Pneumatically operated systems continuously apply a predetermined inflation pressure to the tires. A warning lamp on the nose of the trailer alerts the driver when the system is pumping air to the tires.
Some ATIS not only add pressure to underinflated tires but also reduce pressure when tires become overinflated due to operating heat. These systems are most common on trailers and require no involvement of the driver in their operation.