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March 1, 2009
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Keeping Oil Clean And Dry With Advanced Filter-Dehydration Technology

filter-dehydrationWhile many prior methods have been proven to remove moisture and/or particulates, they involve significant trade-offs, including high cost and limited effectiveness.

When hydraulic and lubricated machines falter, root cause failure analysis often indicates that it is due to oil contamination. To be specific, recent studies confirm that as many as 80% of these equipment failures occur because the oil used contains excessive moisture and particulate contaminants. The machines’ rolling elements and pressure surfaces rely on oil to separate and protect moving components such as gears and roller bearings. Precision control devices such as servo valves are also subject to excessive wear due to contamination.

The thickness of the oil film required in a particular application relates directly to the operating pressures and loads the machine elements will handle, and is directly dependent upon its viscosity grade and temperature. When oil is contaminated with particulates, this contamination can bridge the film thickness gap—encouraging contact fatigue, accelerated wear and additional particle generation. Water contamination has been proven to have significant consequences as well, reducing component life and productivity by leading to equipment rust and corrosion, metal embrittlement, oil oxidation, varnish deposits and changes in oil viscosity.

So, while clean, dry oil optimizes hydraulic and lubricated machine operation, contaminated oil hinders it. Contamination ingression is a continually ongoing process and can be extremely challenging to avoid. In fact, oil sampling has shown that even new oil will often have more contamination than manufacturers recommend for equipment operation. Particulates continue accumulating as the oil is used, generated internally and enhanced by ingress during a hydraulic or lubricated machine’s operation. Although industry has promoted an increased focus on effective filtration in these applications—with high-efficiency (ßeta rated) filtration now widely accepted and OEMs often incorporating full-flow filtration into new equipment—in many cases, manufacturers are noticing the need for further improvements.

Excess moisture can be even more detrimental and challenging to remove, and since water solubility varies based upon oil type and temperature, even a small amount can lead to equipment failure. Water can be present in oil in three states—free, emulsified and dissolved—and typically enters the oil system gradually through condensation, seal leaks or through breathers and unplugged ports. It also can be introduced in significant volumes during equipment washdown and other process conditions or in outdoor locations.

Through the implementation of advanced, patented, fluid conditioning technologies, it is possible to make substantial improvements to the overall fluid condition, reducing moisture contamination by 50-90% and improving ISO Cleanliness by 2-5 ISO Code classes (75-90+%). Fluid condition improvements of this caliber lead directly to enhanced reliability, with the added benefit of simultaneously reduced maintenance and operation expenses.

Removing moisture and the possible costs
Of the multiple oil conditioning methods available, some are better suited for removing one water state over another. For example, centrifuges and coalescing filter/separators can often remove large volumes of free water, but can be sensitive to process fluctuations and may require continual operator intervention. Alternate techniques, such as vacuum dehydration, can remove emulsified and dissolved water, although they are typically costly to install and maintain. Furthermore, the effectiveness of all conventional separators can depend upon the viscosity of the oil, as well as the volume of water needing to be removed.

Water-absorbing cartridges use hygroscopic media to remove trace amounts of free water from oil, and while they are cost-effective to install, they are usually rated in grams of water per element—making them ill suited for systems with ongoing moisture ingression. These cartridges can also prove to be labor- and cost-intensive in applications involving high volumes of water, since they must be replaced once saturated, and they cannot effectively remove emulsified or dissolved water.

Settling tanks remove free water by, as their name indicates, settling moisture and separating it from oil. These are relatively inexpensive but are not designed to remove emulsified water, dissolved water or gases. Plus, their effectiveness depends upon numerous factors, including tank design, residence time, turnover rate, oil viscosity and additive chemistry. Even for smaller applications, a relatively large-sized tank is required, making space limitations another common hurdle to implementing this solution.

For removing larger volumes of moisture from lower-viscosity fluids, centrifuges and coalescing filter/separators have been used to mechanically separate free water using gravitational forces. New centrifuge installations are costly, and with a large number of moving parts, this equipment can be very labor-intensive—requiring dedicated operators. Coalescing filter/separators may require heating and discharge cooling for operation, and they can easily become contaminated from particulates and certain additives.

Vacuum dehydrators (sometimes referred to as vacuum purifiers) are frequently used to remove dissolved and emulsified moisture as well as free water from oil. These systems utilize slipstream (kidney loop) oil circulation and employ a vacuum to lower the boiling point of water, allowing moisture and gases to vaporize out of the oil.Vacuum dehydrators require a moderate-to-high capital investment, and their relatively complex designs can lead to escalated operating and maintenance costs. In addition to requiring trained operators, the systems often involve a heater to increase oil temperature and promote water vaporization, and potentially a cooler to return the oil to a normal temperature after the dehydration process. Plus, as with most oil conditioning equipment, vacuum dehydrators are relatively large and difficult to relocate to different areas of a plant if needed.

Advanced technology without traditional trade-offs
To keep oil clean and dry for optimized equipment life, an advanced filter-dehydration technology was developed that conditions the oil using a simple, low-maintenance design—enhancing particle filtration and removing water in all its states conveniently and cost-effectively. While conventional water and particulate removal alternatives have involved significant trade-offs, this new fluid conditioning system uses the fundamental principles of mass transfer to continuously remove free, emulsified and dissolved water, as well as particulate contaminants— 
without the complex system designs that have required trained operators in past applications.

Mass transfer principles dictate that moisture will naturally diffuse from a region of higher concentration to one of lower concentration. Advanced filter-dehydration systems utilize these principles by ensuring all free, emulsified and dissolved water will diffuse from the oil through the system’s dehydration contactors. First, oil is pumped from the lubricated machine’s reservoir into the system’s high-efficiency particle filter. This filter delivers exceptional results, cleaning the oil beyond levels attained by most full-flow filtration circuits. The oil then flows through the inside of a hollow fiber membrane contactor, while dry air sweeps the exterior surface of the membrane—a design that promotes the diffusion of moisture through the contactor and into the dry air. This air, which now contains dissolved moisture, exits the system through a vent and into atmosphere with no bulk water or other disposables generated in the process. Then, the clean, dry oil returns to the machine’s reservoir.

This innovative filtration-dehydration system can operate at ambient oil temperature with no heat or post-process cooling required, preventing the thermal degradation that can negatively affect equipment and may occur with alternative solutions, such as vacuum dehydrators and coalescers. Another significant benefit of this filter-dehydration system is its simplicity: It requires no routine operator intervention, moving parts, liquid level controls or water drains. Since the only routine replacement component in the system is its coreless particle filter, it offers significant savings in maintenance costs over the prior methods.

System installation and monitoring have also been simplified with this technology. Once a filter-dehydration system is moved into position near a reservoir, users can easily make the required connections for oil supply, oil return, power and compressed air. During its operation, only two system components must be monitored: the differential pressure gauge for particulate filter condition and the oil’s moisture level indicator to determine when conditioning is complete.

Payback from dedicated filter-dehydration
This filter-dehydration technology has been proven to cost-effectively remove contaminants, minimizing equipment wear for improved process uptime and performance—as has been recently demonstrated on a high-speed paper machine. The paper machine’s main lube reservoir had been typically averaging a moisture level of 290 to 530 ppm, with excursions as high as 3770 ppm. Operating under these conditions had typically resulted in more than $100,000 per year in maintenance expense to replace journal bearings. If failures resulted in lost production, the cost escalated by $5-$10K per hour. Since a dedicated filter-dehydration system was installed, the oil has averaged 50 to 100 ppm—potentially tripling the paper mill equipment’s operational life.

The system’s cost-effective, conveniently sized and easy to maintain design has made it an efficient, dependable new oil conditioning method for this and many additional industrial applications, including lubrication and hydraulic systems serving power plants, steam turbine driven equipment, stamping machines and molding presses, as well as steel and roll mills. Furthermore, the unique design of the technology enables it to be scaled in size and capacity to fit the particular conditioning needs of a facility.

A filter-dehydration system has been shown to decrease water concentration down to 25 ppm, and improve particulate filtration to as low as ISO 13/10. It is well suited for periodic use on reservoirs throughout an entire facility, or it may be dedicated to a particular reservoir to provide continuous conditioning, ensuring that oil is optimized without the fluctuations in water concentration that commonly occur with periodic reconditioning. These features ensure that this advanced filter-dehydration technology can reduce oil contamination; minimize wear, maintenance expenses and downtime; and extend hydraulic and lubricated system life. LMT


David Kolstad is a lubrication & hydraulics engineer with Pentair. For more information on the technologies referenced in this article, telephone at (936) 537-1994; e-mail:Davidko@porous.com

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