A filter cleaning service is allowing finishers to improve their operating costs while reducing their environmental impact.

Filter-Doc uses an automated cleaning system to significantly extend the life of filter cartridges.

Sometimes the best solutions are the simplest. For years, powder coating applicators have been using their filter cartridges until they were so loaded with oversprayed powder that they were no longer functional. They would then replace the powder-laden cartridges with costly brand new sets and discard the used ones.

A couple of clever Memphis entrepreneurs, Robert and Greg Murphree, observed this phenomenon and immediately recognized a better way to maintain a powder booth. Their solution is to offer a service of reconditioning the clogged filters and returning the cleaned units to the powder applicator. They formed a company called Filter-Doc and teamed with Filter Equipment Technologies, Inc to establish a process and service to extend the life of filter cartridges from singular use to up to 20 cycles.

Filters are inspected, weighed, tested for pressure differential, and then introduced into an automated cleaning system.

The Problem

Powder coating spray operations typically consist of powder application equipment (guns, feed systems, hoppers, etc), a parts conveyance system and a booth to capture the oversprayed powder. Booths consist of an enclosure, a fan to attract powder-laden air and filters to capture powder. The filters are typically constructed of a carefully engineered medium (treated paper) that traps the powder but allows the air to flow through. The booth usually employs a reverse air pulse or vibration to intermittently dislodge accumulated powder. Eventually the filter becomes saturated with powder, and the fan can no longer adequately convey air through the medium. The oversprayed material then is no longer attracted to the booth and can travel elsewhere in the finisher’s shop, creating a housekeeping issue and potential environmental problems.

When this occurs, many finishers remove the filters and send them to a landfill. This approach is costly and adds to the environmental impact of their process.

The Solution

Filter Doc offers a service that allows a finisher to reuse their powder booth filters up to 20 times.* The finisher has a number of options with this service. In its most fundamental form, dirty filters are removed, packaged and shipped to Filter-Doc. Filter-Doc receives the filters and establishes a database specifically for that finisher. Each filter receives a unique barcode and is logged into the database. Next, the unit is inspected for integrity, weighed, tested for pressure differential, and then introduced into an automated cleaning system provided by Filter Equipment Technologies, Inc. The clean filter is re-weighed, and the pressure differential is tested. At this stage the filter is inspected for damage and excessive wear that may cause the filter to fail during operation. All values are entered into the database, along with the grading condition of the filter, and the cleaned filter is packaged. The entire process takes about a week to complete.

At this point, the finisher can have the filters returned or have Filter-Doc warehouse them until they are needed.

According to Robert and Greg Murphree, since most filters are 3 to 4 ft long and about 14 in. in diameter, and some booths use up to 48 cartridges, using Filter-Doc’s warehousing service can save companies valuable factory floor space.

This service can be carried one step further. A powder coater can buy two sets of filters either from Filter-Doc or another supplier, and Filter-Doc will always keep one clean set until it is needed. They will also replace any worn-out filters at no extra charge. “Companies will no longer need to buy filters unless they are damaged due to misuse. This way a finisher can accurately predict their filter cartridge costs for budgeting purposes,” says Robert Murphree.

Filter-Doc’s tracking system lends itself to operations where strict accounting of processing variables is critical. Not only is each filter bar-coded and tracked, but comprehensive reports are generated for each shipment. These reports list each unit and its manufacturer’s model number, along with initial and final weight and manometer readings, how many times the filter has been cleaned and which Filter-Doc operator performed the service. These reports are sent to the customer after each cleaning and are also available on a password protected section of Filter-Doc’s website.

Robert Murphree and Tom Holman, with Finishing Today’s Lisa Kinateder.


Besides the obvious advantage of greatly extending the life of powder booth filters, the Filter-Doc service offers numerous other benefits.
  • Inspection of filters for integrity and functionality by professional technicians
  • Electronic tracking of filters
  • A reduced burden on local landfills
  • Predictable booth maintenance costs
  • Disposal of worn-out or damaged filters

Future Efforts

Filter-Doc’s cartridge cleaning process has expanded beyond servicing the powder coatings industry. Food processors (e.g. cereals), welding units, pharmaceutical compounders and machine shops have all discovered the value in cleaning rather than discarding their dust collection filter cartridges. Filter-Doc is currently engineering a mobile unit to help facilities that require immediate servicing of their cartridges. Greater implementation of programs such as this will allow finishers to improve their operating costs while reducing their environmental impact.

*The length of reuse is based on filter media type. A polyester media can be reused up to 20 times. Other media reuse rates will vary.

Case Study

A large applicator of automotive powder coatings recently decided to employ Filter-Doc’s services for a portion of their powder application facilities. A total of four facilities participate in this program and have achieved close to $1.0 million annual savings. The savings come from the extended use of the hundreds of filters used in their many application systems, as well as the substantial savings on landfill costs. According to a plant spokesperson, Filter-Doc’s tracking system fits in perfectly with this company’s stringent quality and traceability requirements. Filter-Doc expects to expand this service beyond a fraction of this large automotive company’s needs to save them even more money in the future.

The Process

There are a number of ways to clean cartridge filters. Some involve complicated wet washing followed by drying processes. Others use an ultrasonic dry cleaning technique that sometimes leaves excess residue on media. Filter-Doc uses a unique dry-cleaning technique that utilizes bidirectional compressed air in a closed chamber. The method was developed by Tom Holman, Leon Saba and Harold Zaiser in the 1990s and still bears Harold’s name, even though he passed away in 1999.

The Zaiser method employs streams of carefully regulated compressed air to remove particulates from cartridge filters. The air is blown both from the inside-out and across the exterior surface of the filter medium with nozzles specifically designed for this application. In addition, the cleaning process is augmented by a proprietary agitation system and constant vacuum in the cleaning chamber.

Zaiser cartridge filter dry cleaning units are sold exclusively by Filter Equipment Technologies, Inc. in Cape Coral, FL. The company can be reached at 239.458.8522 orcleanair@filterequpment.com.

Photo by Conroy Studio, Memphis, TN.

For more information about Filter-Doc, contact the company at 901.396.3625, e-mailagmurphree@filter-doc.comorrgmurphree@filter-doc.com, or visitwww.filter-doc.com.