3:40 pm
April 11, 2013
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Adding Secondary Filtration To Lubricated Pumps


This type of contamination removal pays big dividends in terms of improved equipment reliability.

By Dennis Morgan, Des-Case Corporation

It has been well established that contamination is the primary reason for a mechanical system, such as a pump, to fail.  According to MIT professor Ernest Rabinowicz, approximately 70-80% of lost usefulness of industrial machinery can be directly or indirectly attributed to contamination from mechanical and corrosive wear mechanisms (Fig. 1).


The predominant root cause for both types of wear is contamination of the lubricating oil in the machine. In fact, a study conducted jointly by the Society of Tribologists and Lubrication Engineers (STLE) and the National Research Council of Canada (NRCC) found that as much as 82% of mechanical wear of industrial machinery is due to particle contamination of the lubricating oil [Ref. 1]. Removing this contamination is key to significantly extending the life of machines, including oil-lubricated pumps—and adding secondary filtration is an effective way to do it.

The importance of this technology for pumps
Secondary filtration is a contamination removal system that exists outside of the primary lubrication circuit of the machine, typically in a kidney-loop fashion. Its a filtration system that only filters and cleans the oil and does not directly lubricate the bearings. This is also sometimes referred to as oil purification, the advantage of which is not only extending the life of the oil, but also extending the life of the equipment by continuously cleaning the lubricating oil.

There are several methods of oil purification. Although OEMs will sometimes incorporate secondary filtration in their products, this type of filtration typically will be an add-on aftermarket system—in an off-line, side-stream or kidney-loop configuration. Secondary filtration will also usually clean oil down to very low ISO cleanliness levels that primary or OEM filtration cannot.

Most pumps aren’t designed with oil-purification or contamination-removal capabilities. The result is that, over time, contamination has a large negative impact on pump wear. As a pump ages, more contamination is introduced into its lube system, which can cause the pump to fail faster and in a more catastrophic way.

Maintenance personnel across several industries have extended the life of their pumps by adding secondary filtration to their lubricating systems, thus saving not only the costs of replacement or repair of the equipment, but also preventing what’s even more costly—plant downtime.

Consider the following real-life examples of operations that have added secondary filtration to their pumps.

Chemical plant chooses secondary filtration to reduce pump service intervals…
Downtime was the primary concern for one chemical plant that added secondary filtration in a kidney-loop fashion to two of its process pumps. The units are used to move one of the plant’s most profitable products—a highly abrasive one—through the production process. During normal operation, the product will migrate past the pumps’ packing seals and contaminate the lubricating oil. Once that begins to happen, the contamination in the oil causes the packing seals to fail more quickly, which, in turn, causes progressively more product to leak past the seals and contaminate the oil even more.

Prior to the addition of secondary filtration on these two pumps, the maintenance department was changing out 15 gallons of lube oil in each of them every two weeks (on average)—at a cost of at least four hours of downtime each time. (That amount of downtime was due to the complex work required to completely rebuild the displacement sides of these pumps, including re-packing, changing their lubricating oil and cleaning their lube-oil reservoirs.)

Working with its lubrication supplier, the chemical plant added a secondary filtration system that incorporates a simple first-stage bag filter to remove the bulk of the particles larger than 50 microns, and a second-stage micro-fiberglass filter for finer cleanliness. The result was that the pump service interval is now no less than every 12 weeks.


Fig. 2. As shown in these before and after secondary-filtration shots, maintenance personnel at the chemical plant can now re-use lubricating oil over multiple pump service procedures.

The primary driver of the pump maintenance procedure now is wear of the packing seals from the highly abrasive product being pumped—not contamination of the lubricating oil. Moreover, as shown in the before and after images in Fig. 2, maintenance personnel can now re-use lubricating oil over multiple pump service procedures.

The secondary filtration system that led to this dramatic improvement cost approximately $6000, including installation. It saved the facility no less than $25,000 in direct maintenance costs during just the first 12 weeks of implementation. [Ref. 2]

0304descase4Fig. 3. The secondary systems on the hydraulic-pump units at the referenced automobile plant feature first-stage bag filters along with second-stage micro-fiberglass filter elements for fine filtration.Filtration cuts automobile-plant production losses and maintenance costs…
An automobile manufacturing facility wanted to extend the life of their critical hydraulic systems and reduce plant downtime. As part of a proactive and comprehensive equipment reliability upgrade plan, and for trial purposes, this facility added secondary filtration to some of these hydraulic systems. The added secondary filtration systems included a first-stage bag filter followed by second-stage micro-fiberglass filter elements for fine filtration (Fig. 3).

Initially, the facility added these filtration systems to 11 of their hydraulic units in the sheet-metal press area of the plant. Prior to that, the hydraulic systems were averaging an ISO particle count of 24/20/13. As a component of the equipment reliability plan, maintenance personnel set a cleanliness target of 17/15/12. Adding the secondary filtration systems—at a cost of about $10,000 per hydraulic system including installation—resulted in immediately meeting or exceeding that target.

Five months after implementation, there was a 53% reduction in breakdown frequency and a 54% reduction in plant downtime. However, since reductions in component failure from the addition of secondary filtration generally take time to develop, plant personnel believe that their already noteworthy results will only improve.

Overall, the plant’s comprehensive reliability plan, of which secondary filtration is the key component, is expected to return approximately $685,000 per year in reduced production losses and an additional $250,000 per year in reduced maintenance costs. [Ref. 1]

Filtration reduces pump failures in a steel plant…
In a steel plant, the presence of mill scale, dust, dirt and water means contamination is always a major problem. In one plant with approximately 2200 hydraulic pumps, system failures were out of control. The facility’s reliability team attacked the issue by adding secondary filtration to all of their hydraulic pump systems. Incorporating wound-cellulose depth-filter elements, this secondary filtration has reduced pump failures at the site by 96%.

Secondary filtration makes a big difference
There are countless examples of equipment-life extension and downtime reductions resulting from the addition of secondary filtration to critical fluid-handling systems, including screw pumps (and compressors), boiler feed pumps and process pumps, among others. The fact is that any oil-lubricated pump can benefit from the removal of dirt, dust, wear metals, water, process materials, etc.

Pump users have always looked for effective ways to protect and get the most out of their equipment. As the real-world examples in this article show, secondary filtration offers one of the best solutions for doing both. LMT


1. Crane, C., Potteiger, J., “Optimizing Equipment Perfor-mance with Precision Lubrication,” 2013.

2. Lubrication Engineers, Inc., “AMS Filtration System, a Customer Testimonial,” 2009.

Dennis Morgan is the Vice President of Technical Services for Des-Case. The founder of Axle Machine Services, Ltd. (in 1992) and AMS Filtration (in 1997), he joined Des-Case in 2011 when it acquired AMS Filtration. Author of the book, Basic Principles of Vacuum Dehydration, Morgan holds a BSBA degree from Ashland University. Email: dennis.morgan@descase.com.