Filtration has long been recognized for its ability to improve product quality, increase throughput and protect downstream equipment in the production of a vast array of coatings. Due to the predominant use of disposable media filters, however, it was also seen as a necessary contributor to a company's environmental impact. Today, that view is changing as manufacturers are tasked with the strategic corporate mandate to reduce the amount of waste they produce and dispose. As a result, many paint manufacturers are re-evaluating their filtration strategy and turning to self-cleaning filters, which promise not only to minimize waste at the source but also maximize productivity and increase profits.

In accordance with the recommendations of the EPA's Priority Hierarchy of Waste Management, manufacturers have shifted their focus from end-of-pipe pollution controls to minimizing waste at the source. The reasons for this shift are well documented. Minimizing waste at the source provides a cleaner, safer environment; saves resources and money - in some cases, millions of dollars; and reduces long-term risk and liability. Also, by filtering early in the manufacturing process, the cost of filtration decreases significantly since capturing and eliminating undesirable solids is often much more difficult later in the process.

Traditionally, paint engineers have opted for disposable media filters such as bags or cartridges due to their lower initial cost. While initial cost may be lower for small batch operations, this is seldom true for continuous operations, which require a costly, redundant filtration system to maintain production - including piping, valves, support and service connections.

Moreover, there are hidden costs associated with disposable media filters. When users purchase disposable media filters, they often fail to account for the true costs of doing so. There is the initial disposable filter purchase price, which typically runs at least $3 per bag or cartridge per day, plus the ongoing cost of waste disposal. For non-hazardous waste, disposal is $400-$800 per drum, while that of hazardous waste is approaching $1,000 per drum. It's not unusual for the typical paint manufacturer to produce about 20 drums per year of filter media for disposal, not counting the cost of treating or eliminating any run-off process fluids.

There are also labor costs involved with transporting, handling and storing disposable filter media, as well as replacement. For example, for just a small, 30-gpm cartridge filter with six 10-inch cartridges, the operator must remove 16 separate parts including the cover, compression seals, cartridges and seal plates and reassemble all 16 parts with proper alignment to ensure good seals. Then someone must haul away the spent filter media.

There's also a housekeeping cost for cleaning any spillage from disposable media, along with increased emissions, safety risk and liability and the potential cost of disposable media rupturing or overflowing (as bags sometimes do), contaminating product or machinery downstream and slowing production.

Other costs include buying, maintaining and cleaning workers' protective clothing for replacing disposable media, as well as the extra time and labor required to fill out MSDS forms and other paperwork required for items hauled to landfills or incinerators.

The self-cleaning DCF 800 filter is being used by paint manufacturers to reduce costs and waste, and to minimize employee exposure to hazardous materials.

Self-Cleaning Filters: A Bottom-Line-Boosting Alternative

The trend in paint manufacturing is now toward self-cleaning filtration with minimal need for labor. Variations of this, such as disc clean filters (DCF), are helping paint manufacturers to improve profit, worker safety and waste-minimization goals as operations become more efficient.

Though an upfront capital expense, paint companies and their plant engineers are now realizing the extent that self-cleaning filters add to the bottom line. To start with, since a self-cleaning filter system automatically cleans itself while in use, this allows a simple, single piping arrangement; minimal valving; and fewer connections. This translates into lower total system cost and reduced waste. A number of other benefits accrue as well, including:

Automated cleaning minimizes disposal waste and labor costs

With cleanable filter media, there are no bags or cartridges to landfill or incinerate. Self-cleaning filter systems clean themselves within seconds of starting a cleaning cycle. They can be automated to clean themselves according to schedule, or only when necessary.

"Contrary to disposable media, which tend to be replaced according to an arbitrary schedule once a shift, day or week, self-cleaning filters can be automated to clean at precisely the right time," says Roger Weinberg, sales application specialist for RPA Process Technologies, Portage, MI.

"Self-cleaning is controlled by the pressure differential between inlet and outlet headers as contaminants collect on the filter screen," adds Weinberg. "The screens automatically clean themselves when the pressure reaches a predetermined level. This reduces both labor and waste in the filtration process at the source."

Self-cleaning filters not only reduce "waste" but also can turn it into profit

"Dispose of the contaminants, not the filters, to reduce waste and lower disposal costs," advises Weinberg. "Since disposable filter media, especially cartridges, absorb process liquid like a sponge, every time you dispose of a cartridge and its contaminants, you're also disposing of your process liquid." Cleanable media eliminate this source of waste and can be used over and over to dramatically lower disposal costs.

For example, cleaning liquid can often be recycled for additional cleaning, and at times the contaminant itself can be recycled into the manufacturing process as a raw material.

The self-cleaning DCF 1600 from RPA Process Technologies is being used by paint manufacturers as an integral part of production to reduce disposal waste, labor costs and emissions.

Self-cleaning filters dramatically reduce emissions and future liability

Since with disposable media, the filter is opened every time the media is replaced, this can potentially expose workers and the environment to VOCs (volatile organic compounds) or other toxic emissions. Disposable filters also routinely spill some liquid when removed and placed in disposal drums. Quite often, workers simply hose this process liquid to a drain, which adds to potential exposure and waste treatment cost.

Moreover, with disposable filters such as cartridges, contaminants can travel downstream to ruin a product. This can happen, for example, when the knife-edges used to seal cartridges get nicked and permit solids to bypass the media. Contamination can also occur if cartridges aren't stacked properly in the housing, which is a common problem. In some cases, even the media itself can shed and cause downstream contamination.

With a self-cleaning filter, however, the filter is opened only for inspection. This drastically reduces emissions and their potential risks. "Positive elastomeric-to-metal seals can virtually eliminate off-spec product due to solids bypassing the filter media," adds Weinberg. "Because cleanable media are seldom removed from the housing, seal failure almost never occurs. What's more, reducing waste with cleanable media not only minimizes current worker safety and landfill liability, but also that from legislation that could require costly clean-up years from now."

Minimum Waste and Maximum Profits

Despite increased environmental pressures, regulatory requirements and yield targets, as well as shrinking profits, staffing and capital budgets, the paint industry now has at least one strategic response - increasing its use of self-cleaning filters to minimize waste at its source while boosting productivity and profits. With the EPA listing source reduction as its most desirable technique of waste management and the public more concerned than ever about environmental issues, self-cleaning filter technology seems to have established itself in the paint industry at an opportune time.

For more information on self-cleaning filter technology, write to RPA Process Technologies, Inc. at 9151 Shaver Road, Portage, MI 49024-6798, USA; call 866-867-2893 toll free; fax 269-323-2403; or visit

Self-Cleaning Filter Success

PPG Architectural Finishes, a latex paint and stain manufacturer in Louisville, KY, knew its filling operation was overly complicated, noisy and required far too much operator attention. More importantly, PPG experienced an unacceptable percentage of product loss in the filtering process.

An air-operated diaphragm pump at the base of a blend tank pumped product onto a large, open, vibrating screen. Product exiting the vibrating screen fed into an accumulating vessel, where another pump transferred product through a polishing filter into a rotary drum-filling machine. With the two pumps, vibrating screen and open-air vessel, the system was complex, noisy and wasteful.

To stay competitive in the tough, low-margin paint industry, Doug Story, plant engineer at the Louisville site, aimed to streamline the company's filling operation. His goals: to produce as much finished product as possible, using the least wasteful, most environmentally friendly methods available.

In consultation with RPA Process, PPG replaced its vibrating screen, accumulating vessel and diaphragm pump with a DCF-800 mechanically cleaned filter. Removing the vibrating screen eliminated the need for the accumulating vessel, associated piping and controls, as well as the second diaphragm and its compressed air components and controls.

With the DCF filter, paint enters the top inlet of the filter housing and passes through the screen. The screen holds undispersed pigments, paint skins and debris, while cleaned paint exits the bottom outlet of the filter. A cleaning disc moves up and down the filter screen, removing debris. With the aid of the downward fluid flow and the disc movement, the debris is deposited into a holding chamber at the bottom of the filter housing and is regularly purged from the housing via a valve at the bottom of the chamber. "The simplicity of the new filling process gained instant approval from both our operators and maintenance personnel," said Story.

The DCF filter has virtually eliminated operator involvement in the operation, and removing the vibrating screen and second diaphragm pump has dramatically reduced noise levels. The DCF filter purges residual paint and debris into the plant recycling system, where the solids are separated and the paint is reused. This purge system allows filtration and cleaning to occur simultaneously.

Due to the DCF filter's top-to-bottom flow design and debris-purging technology, Story reports significant reductions in product waste. "Post-installation cost for the first year was under $10," says Story. "Payback was achieved in four months, and this analysis does not include the savings generated in utility costs for the vibrating screen, its maintenance or additional operator time. The DCF filter has contributed to our paint and stain production efficiency, and exceeded the objectives set at the beginning of the project. It also provides our workers with a quieter, more environmentally friendly workplace."

Self-Cleaning Filters Improve Plant Efficiency and Profits

A nationally recognized, New York-based paint manufacturer also found self-cleaning filters to be their answer. When the New York paint manufacturer made a commitment to its plant's extensive recycling and reuse program, its process engineers looked at the bag filter system used on the paint line and decided there was room for improvement.

At a cost to the company and environment, the fabric bag filters used with latex-based paints were rinsed and landfilled. Additionally, production-stopping filter change-outs occurred too often due to solids accumulating in the bag filters. As solids accumulated, product flow through the bag filters decreased, resulting in longer fill times until the operator shut down production to change bags. Sometimes change-out occurred as frequently as every 15 minutes. Finally, because the bag filter system was messy, it was mounted on a four-wheel cart to allow bag filter access and cleanup of the surrounding area after change-out.

One of the biggest production bottlenecks in the latex paint operation was the time required by operators to change bag filters. Canning operators on the fill line continually waited for bag filter changes. In fact, because the line had to shut down every time the bags were changed, operators were rated on how quickly they could change out the bags. Process engineers replaced the bag filters on one of the one-gallon can fill lines with an RPA Process, DCF-800, self-cleaning filter. The DCF allows filtration and cleaning to occur simultaneously, which maximizes production. This eliminated the need to landfill bag filters and took advantage of the DCF filter's higher flow rates. The resulting flow rates were better than anticipated, and increased the paint line's output almost three-fold.

By switching from bag filter to the DCF, engineers were able to expand the fill line and convert it from batch to semi-continuous process. That resulted in production rates of about 10,000 gallons (37,500 l/min) of paint canned per day to an average of 25,000 gallons (94,500 l/min) per day. A significant portion of the increase is due directly to the self-cleaning filter's efficiency.

The DCF's filtering screen has a 150- or 230-micron retention size, depending on the quality dictated by the application. At set intervals, or pre-determined changes in pressure, the DCF cleans the filtering screen then purges the trapped solids, without interrupting production. Now the paint line operators are waiting for the canning operators.

Impressed with the DCF-800 filter's increased flow rates, engineers decided to take the next step and install a larger-capacity DCF-1600 filter on a five-gallon can fill line. Due to the DCF-1600 filter's superior performance, the New York paint company plans to install an additional DCF-1600 filter in the plant, as well as replace the original DCF-800 filter with a DCF-1600 filter, as the paint line expands.

Replacing disposable bag filters with the DCF self-cleaning system eliminated production downtime caused by filter changing and costly landfilling procedures. The end result not only significantly improved plant efficiency and profits, but also contributed to a cleaner plant and environment.