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There are plenty of articles and resources regarding the proper design and installation of new dust collection systems, as well as checklists and protocols for preventative maintenance. By contrast, this article series seeks to address the topic of My dust collector is not working. What should I do now? The articles will identify and define the most prevalent failure modes in a dust collector. Then, they will elaborate on steps to diagnose and potentially troubleshoot the issues. For purposes of this article, a dust collector will be generally defined as a self-cleaning media-type unit – specifically a baghouse or a cartridge collector. (Cyclones, mist collectors, and other devices are not considered here.)
A failure mode is a specific problem or shortcoming that is the result or symptom of a non-performing or under-performing system. Failure mode does not have to mean complete failure or non-operation. The term is used here to identify target areas that are not working as designed. In the more extreme cases, the failure mode causes the unit/system (or manufacturing process) to be non-operational. There are certainly many other failure modes, but the four listed above are the most prevalent.
Note: This series intentionally excludes the failure modes of fire and explosion, which are more complex and deserving of a separate analysis. Additionally, extreme caution should be exercised when considering any troubleshooting or corrective action suggestions. Even seemingly-simple items should be done only by qualified and trained personnel with appropriate levels of personal protective equipment and safety precautions, such as lock-out tag-out, fall protection, confined space protocols, etc. Electric items should only be addressed by qualified electricians. When in doubt, call a professional to perform all work. A dust collector manufacturer will likely be able to provide a local referral.
By Coby Jenkins, Donaldson Torit Regional Service Engineer
Identifying a Leak
A continuous dust discharge from your dust collector is often an indication of a problem within the collector. Leaking collectors are usually diagnosed by simple visual observation. If there is a visible plume or emission from the clean-side of the dust collector, it can most likely be attributed to a problem with system integrity. The resulting leak be caused by any of the following:
Most leaking collectors start with filter media issues, whether it is on a bag or a cartridge filter. Some mechanical leaks, however, may be found in the tubesheet area of the dust collector. The tubesheet is the structural area of the dust collector that separates the dirty air plenum from the clean air plenum. (See Figure 1)
Trying to identify a specific leak and a corrective action can sometimes be difficult. In some cases, the leak may be the result of abrasion inside the unit itself. (Figure 2 shows actual wear inside a collector that has resulted in a hole)
How long have the filters been installed and/or is it time for new filters?
What is the operating differential pressure loss across the filters, and has it changed recently?
Inspect filter access covers. Are they loose, misaligned, or damaged?
Inspect filter access cover gaskets. Are they torn or poorly compressed?
Are the filters installed correctly?
Is all the filter attachment hardware in place and properly tightened?
A single missing bolt creates a hole in the tubesheet that can allow a very significant amount of dust to bypass the filters.
Is dust building up on the clean side of the tubesheet? If so, where? This may help identify the location of mechanical leaks.
If you can monitor the leak and relate it to pulse cleaning of a certain section of the collector, you can narrow your search for mechanical leaks. This feature is often available with broken bag detectors.
Check the filter housing for cracks and/or damaged welds.
Removing and visually inspecting filters for signs of damage or mechanical defects may identify the cause of leaks. Filters can experience damage from abrasion. They can also be damaged from operational upset conditions, such as temperature excursions (too high or too low), process chemical imbalances, unexpected sparks or embers, or excessive cleaning frequency. If damage is identified, filter replacement can correct the leak, but additional questions should be asked to identify the underlying cause of the damage.
Before replacement filters are installed, be sure to wipe down and clean the tubesheet, existing filters, and the filter access covers. Material buildup in any of these areas or positioning errors during installation may allow new leaks to develop.
If a simple visual inspection (as outlined above) does not locate the leak, a more extensive leak-test with fluorescent tracing powder may be required. Very fine, fluorescent powder is added to the dirty side of the collector while the collector is run for a brief period of time. The collector is then shut down, and the clean air side is inspected using a special detection light (black light) to illuminate the clean side of the collector. If leaks are present, the fluorescent tracing powder (which passed through the leaks) will glow very brightly. This will make it very easy to spot the point of the leaks.
Although fluorescent tracing powder and detection lights are readily available commercially, this type of testing is more commonly performed by professional dust collector service businesses and organizations. In some instances, different colors of powder may be used to confirm effective corrective actions after the initial tests locate the leaks.
As leaks are located, it is good practice to take corrective actions for each leak before moving to the next potential leak zone. This removes the need to mark or track leaks for later corrective action. Once all the zones have been reviewed and the potential root causes addressed, the collector can be restarted and evaluated. However, before the collector is put back into operation, it is important to ensure the clean air plenum has been thoroughly cleaned of any prior dust accumulations. Removing dust from the clean air plenum avoids that dust being discharged back into the facility. This speaks to the importance of cleaning/wiping down the following areas before restarting the collector:
Dust collector leaks can happen to anyone, but the causes are often easy to identify and easy to remedy. If leaks continue to develop, or if they persist after you complete your troubleshooting, contact your local dust collection supplier for assistance. There are many ways to reduce the potential for leaks to develop, and they may be able to help you attain a leak-free operation for your collectors.