Understanding Diesel Particulate Filters And Their Significance As It Relates To Used Semi Trucks

Posted on: 13 August 2015

When purchasing a used semi truck from an online dealer like http://www.arrowtruck.com/, there are a lot of considerations that must be kept in mind in order to avoid choosing the wrong vehicle. Everything from tires to the cab to the fifth wheel must be checked for excessive wear and tear; however, one vehicle component that can be easily overlooked by prospective buyers is the diesel particulate filter (DPF). This part is critical to the operation of the truck, not only from a mechanical point-of-view but also from a legal perspective. Below is more information about the DPF as well as how you can check it and properly clean its internal parts:

The diesel particulate filter explained

Diesel particulate filters are tasked with removing soot from the exhaust stream of semi trucks. Also used with off-road diesel engines, particulate filters capture the small, unburned particles of diesel that form the grimy black coating on exhaust pipes. These particles can significantly affect human health and contribute to respiratory disease.

While there are different kinds of particulate filters, the most common kind in use consists of a perforated ceramic core. Tiny passages crisscross the interior of the filter, and soot is captured as the exhaust flows through it. As the soot builds, heat from the engine automatically burns the soot so that nothing remains but a small amount of ash and harmless gases.

In some cases, the diesel particulate filter needs extra attention to remove the accumulated soot. If that occurs, the engine will either automatically generate extra heat by burning fuel inside the filter or by the operator activating a manual burn process, also called regeneration. The ash byproduct must be periodically removed from its holding canister by a technician or the operator.

Consequences from lack of maintenance

If a diesel particulate filter is poorly maintained, such as if the driver cancels the automatic regeneration process repeatedly or fails to manually regenerate the filter when needed, there are several possible negative consequences. In some situations, the back-pressure behind the filter will begin to build to excessive levels, and this increase can cause internal engine damage. Another possible problem is that the particulate filter can be ruined and require replacement or repair. However, the most dangerous possibility is the increased risk of engine fire; combining increases in heat with high accumulations of soot are a recipe for catastrophic fire.

How to check the diesel particulate filter for proper maintenance

If you are buying a used truck, you should know a few things to look for when inspecting a truck's diesel particulate filter. The first step is easiest; simply sit in the driver's seat of the cab and turn on the ignition. Look for the diesel particulate filter indicator light and reference the truck manual for normal operation. If the light is flashing or contains an extra warning indicator that is illuminated, the filter is probably in need of regeneration.

Another area to check is the ash box on the diesel particulate filter. This box should be emptied at least once per year, sometimes more, in order to remove the particles in exhaust that simply would not burn. If the box contains a lot of ash, be wary of purchasing the truck without first looking for other maintenance negligence.

Finally, have a trusted technician operate an exhaust backpressure test to see if the truck is satisfactorily running. High backpressures indicate possible soot clogging in the ceramic core.

Regenerate the diesel particulate filter

After the filter is inspected and the other tests are run, then you can perform a filter clearing procedure. While you should consult your truck's reference manual or repair manual for specifics, most semi trucks regenerate themselves using an automatic or semi-automatic process. Initiate the process by parking the truck and being sure that all persons are clear from being burned by high exhaust temperature. In addition, keep the truck away from flammable materials such as straw or cardboard boxes. Allow the regeneration process to run as long as necessary; avoid interrupting the regeneration cycle to maintain a high level of cleaning.