provide training for school bus technicians? Because they will need training on removing and installing; cleaning procedures and diagnostics.” Drew Taylor, global marketing director for FSX, which builds diesel particulate filter
cleaning systems, suggests cleaning DPFs and DOCs on school buses on a more acceler- ated basis. He suggests once every 50,000 to miles to protect the investment. “Te DPF’s/DOC’s are expensive, but the good news is they do a great job,” Taylor said.
“Tey protect the community at large from diesel soot, which is a very dangerous carci- nogenic substance. Te bad news is they are somewhat more fragile than what we once thought and must be maintained properly. Tey are made to filter soot but it is the other
substances that get caught up in them that can destroy the filters.” Te DPF traps particulate matter, or ash,
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and removes it from the diesel exhaust stream before it goes into the atmosphere. Passive and active regeneration systems clean the filters by using heat to oxidize the trapped particulate matter. But Dale Puhrmann, national bus sales manager at TRP Bus Parts, said effective passive re- generation is rarer in school buses than in trucks because of abnormal operating conditions of increased idle time coupled with stop-and-go routes. Due to the result- ing, lower school-bus engine temperatures, soot develops and clogs the filter. He rec- ommended professional cleaning of DPFs once or twice a year.
❝ My advice is to not
look at just retro- fit cost but look at cleaning intervals of each proposal. Labor is also a part of the
cleaning cost. ❞ — Mark Ehlers, Navistar
“In reading the manufacturer recom-
mendations (for trucks), you wouldn’t conclude that you have to clean the DPF as much as you do,” he added. Both DPF types must be removed and
cleaned periodically of ash or soot, again two different things, that can build up and plug and crack the filters. Te DOC uses a chemical process to clean the exhaust from the nitrogen-rich diesel fuel of NOx. Taylor said a DPF costs about $2,500 and
www.TransTechs.com 888-637-3776
64 School Transportation News Magazine July 2012
a DOC about $3,000 because of more pre- cious metals. Stage-one cleaning for a filter that is regularly maintained is about $250, excluding labor. If it is neglected and has to be baked, the cost can nearly double. “I strongly suggest the need for more
proactive exhaust filter maintenance to ensure longer life for the filters and peak engine performance,” Taylor said. n
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