What experience has revealed about diesel particulate filters

What we know about diesel particulate filters we didn’t know back in august 2009.

3. How often does a DPF need cleaning? In general, for heavy duty trucks using low ash oil, the DPF should be cleaned once annually or every 150,000 miles; less for severe-service applications. For medium duty trucks using low ash oil, cleaning should be every 75,000 miles. These intervals can vary depending on application.

Ash left longer in the DPF begins to set up and harden, making cleaning difficult.

These intervals are based on the real world experience of FSX from many years of cleaning more DPFs.

DPFs should be “inspected and verified suitable for re-use,” advises David McNeill, parts and service manager at Cummins Service Solutions. DPFs that are improperly cleaned or not cleaned at regular intervals are most likely to require replacement.

Filters cleaned at proper intervals “result in improved DPF reliability and durability, as well as reduce the likelihood of frequent regenerations (combustion at high temperatures of the PM within the filter) and associated downtime,” he notes.

4. How can the DPF affect the resale price of a used truck? If a DPF is in poor condition it will need to be replaced and that can add to a used truck’s price tag.

To avoid a disputed appraisal, never sell a used truck that has a plugged DPF and soot blackened stacks (one sign of a failed DPF). Also have on-hand cleaning documentation showing proof of annual cleaning with inspection notes showing restriction before and after each cleaning.

Steve Clough of Arrow Truck Sales (www.arrowtruck.com), a seller of used commercial vehicles, feels truck builders did not do a good job of communicating how DPFs should be maintained and that led to problems for customers.

“Our first experience with selling used DPF trucks was not a good one,” he says. “As a result, we do things a lot differently today, including making sure the DPFs are cleaned before the trucks are sold to anyone.”

5. Should the diesel oxidation catalyst (DOC) be cleaned along with the DPF? We recommend five minutes of a Stage 1 pneumatic blowout for the DOC.

6. What is the ROI for a fleet owning a DPF cleaner and how large does a fleet need to be to justify owning a DPF cleaner versus contracting out the cleaning? It’s been our experience at FSX that it is more cost-effective to own a DPF cleaner rather than contract with a DPF cleaning service when a fleet has at least 100 DPF-equipped trucks. Such a fleet would pay for the equipment in about one year. The return on investment goes up from there.

7. What happens when DPF cleaning is ignored all altogether? The cells inside the DPF fill with ash. The ash hardens and eventually the DPF plugs, cracks, glazes or melts, destroying the DPF. That, in turn, results in vehicle downtime and added expense. An OEM replacement filter costs around $3,000.

Thus, this makes cleaning or exchanging the DPF the best option for most truck operators. Prices charged for DPF cleaning range between $350 and $500, depending on location and the cleaning method used.

Some manufacturers offer exchange programs in lieu of cleaning, which usually run between $600 and $800 per filter.

8. What DPF cleaning tool should I buy? DPF cleaning systems have been in use for years now and there are a variety to choose from. Do your homework before purchasing one. Key things to keep in mind include:

  • Is the DPF cleaner OEM tested or recommended?
  • What is the method of cleaning?
  • What are the air compressor size and the cubic feet per minute (cfm)/psi rating? (The more powerful the compressor, the more effective and thorough the cleaning.)
  • Is the DPF cleaning process visible to the technician? This allows a technician to spot any possible failures, such as cracking.
  • Remember, you get what you pay for.

Careful attention needs to be paid to choosing a DPF cleaning service as well.

9. What is the future of the DPF? It is doubtful that DPF technology will become obsolete any time soon as many improvements are being made to diesel emission control systems. Developments include thinner ceramic substrate walls for backpressure reduction; changes in microstructure and porosity of the ceramic media to improve filtration efficiency; increased ash storage capacity with the use of asymmetrical cell technology; and further reduction of nitrogen oxides through the use of NH3 (ammonia) from urea for selective catalytic reduction (SCR) diesel engine emissions control technologies. This technology can now be incorporated as a coating on the DPF itself to perform the same function as the more traditional separate DOC.

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