Anatomy of an Oil Filter

Article extract from ReliablePlant newsletter:
http://www.machinerylubrication.com/Read/29396/oil-filter-anatomy

This is the second part of a series of “anatomy” lessons within Machinery Lubrication. In this issue, the oil filter will be examined to uncover its functional and performance characteristics. Several other related topics will also be discussed, including best practices for oil filter usage, possible filter failure modes, factors for proper filter selection and how to maintain an installed filter.

By definition, an oil filter’s main role is to cleanse oil from destructive contaminants within a machine such as an engine, transmission, hydraulic system and other oil-dependent systems. In the case of automotive oil filters, canister-type filters are the most common. This filter configuration was most likely responsible for the advanced performance of oil filtration technology.

In 1922, Ernest Sweetland invented the first oil filter device for automobiles. It was named the “Purolator,” which was short for “pure oil later.” The spin-on filters common in today’s automotive industry were introduced in the 1950s and were virtually a standard by the early 1970s.

Aside from the automotive industry, oil filtration is an integral part of equipment within a wide variety of industries, including aerospace, power generation, oil refining, manufacturing, mining, etc. Although most current oil filter designs come in canister or cartridge types, several variations in size, filter media, dirt-holding capacities and flow arrangements are available. For this reason, it is important that filters and filtration systems are selected to meet the needs of the application and with cost, performance, ease of use and environmental conditions in mind.

Oil Filter Types

Oil filters can be characterized by the method in which the contaminants are filtered or the method in which the oil flows through the housing. One technique used to control contamination in filters is through surface-type media. This is the type of filter used in automobiles. In depth-type filters, the filter media are designed to hold much higher levels of contamination and provide a more circuitous path for lubricant contaminants to become trapped.



Other possible contamination control methods include magnetic and centrifugal filtration. Magnetic filtration utilizes rare-earth magnets or electromagnets to attract and collect ferrous particles as the oil passes through a magnetic flux region. Centrifugal filtration works by integrating a rapidly rotating cylinder to produce a centrifugal force for contamination separation from the oil.

Oil filters can also be categorized by the oil flow design. As its name implies, a full-flow filter will draw all of the oil through the filter media. On the other hand, a bypass filter only requires a fraction of the oil flow for sufficient flow rates within the system. The application’s oil flow and contamination control requirements will determine which design is the best option. Another alternative is the duplex filter system, which contains two side-by-side filters in parallel to allow one of the filters to be replaced during uninterrupted operation.

With typical canister-type filters, it is standard for oil to flow from the outside in. This means that the oil travels through the cylindrical filter media from the outward-facing surface into the inner core. However, in some cases the flow direction is reversed, with the oil coming into the filter through the core and pushed outward through a unique pleat design. This is intended to improve flow handling and distribution as well as reduce filter element size.

Filtration Mechanisms and Filter Media

A filter’s primary function is to remove and retain contaminants as oil flows through the porous component called the media. The media operate under several types of filtration mechanisms, including:

• Direct Interception and Depth Entrapment – Particle blockage on the media due to the particles being larger than the taken passages within the media.
• Adsorption – The electrostatic or molecular attraction of particles between the particles and the media.
• Inertial Impaction – Particles are impacted onto the filter media by inertia and held there by adsorption as the oil flows around.
• Brownian Movement – This causes particles smaller than 1 micron to move irrespectively of the fluid flow and results in the particles being adsorbed by media in close proximity. It is much less prevalent, especially in viscous fluids.
• Gravitation Effects – These allow much larger particles to settle away from fluid flow regions when there is low flow.

In addition, filter media can be designed to capture particles through two distinct methods:

• Surface Retention – Contaminants are held at the surface of the media. This provides an opportunity for the contaminant to become trapped as it comes in contact with the media surface.
• Depth Retention – Contaminants are held either at the surface of the media or within the labyrinth of passages within the “depth” of the filter media. This creates several opportunities for contaminants to become trapped.

The graph below shows how depth-type filtration is more efficient in capturing smaller particles when compared to surface-type filters. This can be attributed to the deeper media providing more chances for the particles to be trapped along with the adsorptive and Brownian movement effects being more predominant in depth-type filters. While these characteristics are beneficial, depth-type filters tend to have higher differential pressure across the media as a result of the increased flow restriction from the deeper filter media.

Particle size retention characteristics of
depth-type and surface-type filter media.

Filter Media Types and Dirt-Holding Capacity

In the September-October 2012 issue of Machinery Lubrication, Wes Cash explained how the porosity of the filter media plays a role in how well the filter can retain captured particles. This is known as the dirt-holding capacity. As pore size goes down, to maintain a low differential pressure across the media, the pore density must go up to account for the oil volume in contact with the surface. The filter depth and size also influence the dirt-holding capacity. Another factor is the filter media material. There are three primary types of filter media:

1. Cellulose - Comprised of wood pulp with large fibers and an inconsistent pore size.
2. Fiberglass (Synthetic) - Comprised of smaller, man-made glass fibers with a more consistent pore size.
3. Composite - Comprised of a combination of cellulose and fiberglass material.

Cellulose media are advantageous because they can absorb some water contamination. However, these types of media tend to fail more rapidly than synthetic media in acidic and harsh oil conditions. Nevertheless, the primary reason synthetic filter media are preferred is their more consistent porosity and smaller fiber size, which contributes to higher dirt-holding capacity and longevity of the filter.

This example of a depth-type filter has an element that requires
oil to pass through 114 millimeters of filter media
for maximum particle filtration. (Courtesy Triple R)

Understanding the Beta Rating

Oil filters are rated by a technique called the beta rating. In his Machinery Lubrication article “Understanding Filter Efficiency and Beta Ratios,” Jeremy Wright explained the methodology behind the beta rating in more detail. In short, the beta ratio is calculated by dividing the number of particles larger than a certain size upstream of the filter by the number of particles of the same size downstream of the filter. Every filter will have multiple beta ratios for different particle size limits such as 2, 5 or 10 microns.

Best Practices for Oil Filter Usage

Storage - Filters can fail long before they are to be used for their intended purpose. Therefore, proper filter storage and handling are essential. Ensure filters are kept clean, cool and dry, and always follow the first-in/first-out rule.

Installation - Even if a filter installation seems simple and routine, refer to the manufacturer’s recommendations for proper procedures. A classic mistake is over-tightening. Most recommendations suggest that a three-quarter turn after seal contact is optimal. Over- or under-tightening can inhibit the seal’s longevity and effectiveness. Confirm that connections, seals and ducts are fitted appropriately and are free of contaminants.

Avoiding Pre-fill - In most cases, you do not want to pre-fill your oil filters before installation. In diesel engines, it is recommended that a pre-lube system be installed instead in order to counteract changes from dry-start conditions.

Choosing Correctly - Many filters and filter housings are designed to be interchangeable, so just because a particular filter fits doesn’t mean it is the correct filter. Make sure each filter is replaced with the right filter. This may not necessarily be the one found on the machine, as an incorrect filter might have been used during the last filter change.

Training - Proper training must be conducted for all personnel involved with changing filters. Remember, a task that seems straightforward to most people may not be for a new employee.

Filter Failure Modes

Channeling - During high differential pressures, filter media passages can enlarge to a point where unfiltered oil can pass through without an efficient contaminant capture. In addition, any particles that were previously contained within the filter in line with the enlarged passage may now be set free.

Fatigue Cracks - In cyclic flow conditions, cracks can form within the filter media, allowing a breach of oil to pass through unfiltered.

Media Migration - Media fibers can deteriorate and produce new contaminants made up of filter material. This may be caused by improper placement of the filter housing or an inadequate fitting of the filter, which can generate damaging vibrations. Embrittlement from incompatible oils or extremely high differential pressures can also result in media disintegration.

Plugging - During operation, filter media can become fully plugged by exceeding the dirt-holding capacity. Plugging can occur prematurely if excessive moisture, coolant or oxidative products like sludge are present.

61%	of lubrication professionals say filter plugging is the failure mode seen most frequently in oil filters at their plant based on a recent survey at machinerylubrication.com

Factors for Proper Oil Filter Selection

Structural Integrity - Arguably the most critical factor, structural integrity relates to a filter’s ability to prevent the passage of oil through an unfiltered flow path. The International Organization for Standardization (ISO) has established procedures for testing fabrication integrity, material compatibility, end load and flow fatigue. These tests can reveal defects such as improper sealing of seams and end caps or breaks in the media from high-flow conditions, as well as the effects of high temperatures on the filter element.

Contamination (Dirt-Holding) Capacity - This refers to the amount of contaminants that can be loaded onto the filter before the filter’s efficiency is limited.

Pressure Loss - This involves the overall differential pressure lost from the filter’s placement on the system. The pressure loss will be influenced by the filter media’s porosity and surface area.

Particle Capture Efficiency - This is the overall effectiveness of the filtration mechanisms within the filter media to extract and retain contaminants from the oil.

System/Environment - The characteristics of the system and environment in which the filter will be installed must be considered, including the contamination expectations, flow rates, location, vibration, etc.

Maintaining Installed Filters

The best way to prevent filters from reaching their dirt-holding capacity is to avoid contaminants in the system from the beginning. The fewer external contaminants that ingress, the fewer contaminants that are generated internally (particles produce particles). Use the following guidelines to maintain installed filters:

• Ensure proper breathers are installed to prevent contaminants and moisture from entering the system.
• Keep seals and cylinders clean and dry by using appropriate wipers and boots.
• Select the appropriate oil grade and additive package to counter contaminant ingression and internal friction.

Analyzing the Filter

A filter not only is a trap for the machine’s undesirables but also a concentration of clues as to what’s occurring within the machine. Particles within the oil may be so highly diluted that practical analysis can become a daunting challenge. However, the particles trapped in the filter may be so plentiful that they can be easily visible to the naked eye.

Metal contaminants are a primary indication of an issue within the machine. Although some amount of metal contaminants can be expected, an unusual amount should be recognized by trending the filter’s visual appearance after each oil change. Cutting open the filter and suspending a strong magnet over it can aid in pulling out the metal contaminants to more easily distinguish them.

If the machine is suspected to have an issue, the filter should not be discarded, as this would be similar to throwing away key pieces of evidence. Maintain the filter in the same condition as when it was removed and have it analyzed by the manufacturer or a laboratory.

Filter Disposal

Oil filters are not designed to be dumped into any wastebasket. Increasing regulations by the Environmental Protection Agency dictate proper filter disposal. While each type of oil filter may have its own requirements, common practices include oil draining, crushing or incinerating the filter. Many disposal services or filter distribution centers will accept used oil filters at little or no cost.

.

References

Fitch, E.C., An encyclopedia of contamination control, 1980s
Fitch, E.C., “How to Select Fluid Power Filters,” The BFPR Journal, 1979, 12, 3, 197-201
Erosion Control, Equipment World Magazine, December 1991
Filtration Manual, PTI Technologies Inc., 1990
Pall Corporation, Ultipleat SRT Filter Brochure, Nov. 2007
Triple R Oil Cleaning Products, Product Brochure, 2013

Machinery Lubrication (6/2013)

About the Author

Bennett Fitch

  Bennett Fitch is a technical consultant with Noria Corporation. He is a mechanical engineer who holds a Machine Lubricant Analyst (MLA) Level III certification and a Machine Lubrication ... Read More

Best Strategies for Managing Varnish

Article extract from ReliablePlant newsletter:
http://www.machinerylubrication.com/Read/29354/managing-varnish-strategies

Varnish is the product of a chemical reaction within oil which leads to a new chemistry being created that is different from both the oil and its additives. A prevalent varnish begins as an acid, which is typically caused by a reaction of the oil’s additives as they become consumed or the base oil’s chemistry as it is degrading. It may also result from a reaction of the oil with other chemistries, which may be present as contaminants within the oil or the system. As with other lubricant-related properties or associated machine conditions, condition-monitoring techniques can be used to assess the accumulation of varnish within oil and manage the detrimental effects that follow.

Condition Monitoring

Lubricant condition monitoring involves obtaining data that supports an evaluation of the acceptability of the machine performance and the viability of the oil. To date, deposits on lubricated equipment have been the focus with regards to the detrimental effects of varnish. Figure 1 shows examples of bearings with significant varnish accumulation.

In general, the alarm and action criteria used within industry are set at levels to avoid power loss or machinery damage but may not include the prevention of varnish deposits. This discounts the effect varnish has on the design and performance of the oil and may allow oil to remain in service when it has exceeded failure criteria.

A principal area of lubricant condition monitoring that can often be overlooked is the suitability for continued use of the oil. This type of monitoring determines if the oil is able to meet its design properties. When outside of these criteria, the oil can be considered to be in a failure mode. Unfortunately, this aspect of lubricant condition monitoring appears to have become lost in comparison to the significant machinery impacts seen when varnish is found in turbine systems.

Figure 1. These heavy varnish deposits
were found on bearing surfaces.
(Courtesy Fluitec International)

If oil condition was the focus of monitoring rather than machine condition, then varnish likely would not progress to the point of accumulation and the oil would be much more capable of meeting its design. This type of lubricant condition monitoring should be emphasized when performing varnish-related monitoring since oil with a high varnish load can be expected to have critical loss in key design characteristics such as water separability and inhibiting corrosion/rust, foam and air release. Loss of any of these properties can place the system at significant risk. Testing criteria that focus on these properties should be at the forefront of the varnish issue.

Varnish Basics

The typical varnish progression begins with a reaction at the molecular level. This generally includes an oxygen molecule. In oil, the oxidized molecule is controlled through additives, which inhibit it from accelerating the degradation of the remaining oil. As more varnish forms, it becomes distinct particles that can be measured in nanometer-sized particles. As the numbers of these particles increase, this degradation material within the oil can be described as a varnish cloud of nanometer-sized material. When the cloud density oversaturates the oil, some of the varnish material will settle out within the lubrication system (like rain falling from the sky) in the form of a deposit. In time, the deposit can harden into a solid material, which is commonly known as varnish.

Oil Saturation

Turbine oil is designed to hold and manage a finite volume of varnish material. When this capacity is exceeded, the oil is considered saturated. Deposits can then form and accumulate in the system. Saturation has a relationship with temperature in that oil at a higher temperature is able to retain a greater volume of the nanometer-sized varnish material than oil at a lower temperature.

Figure 2. Varnish can occur in any system.
(Courtesy Paul Sly, Chevron)

The desired system condition for new oil would be to install the oil into a clean system so the progression of oil degradation and subsequent varnish accumulation would be limited to natural degradation of the oil. This degradation progression should be limited to the influences of new varnish created within the system as opposed to existing system varnish, which is known to accelerate oil oxidation.

It is important to install oil into a clean system so the maintenance sensitivity will more appropriately respond to the oil’s initial varnish saturation level as an oil failure criterion. This sensitivity should be maintained at the lowest expected system oil temperature rather than at a higher temperature, since deposits will form and collect in a system at this lower temperature, and deposit formation should be considered a lubricant failure mode.

Base Oil Influence

Varnish accumulation is also influenced by the base oil category, as designated by the American Petroleum Institute (API). Group II base oils have a superior design and can be expected to provide improved performance over Group I base oils, assuming that the system in which the oil is installed is clean. Both Group I and II base oils have inherent solvency, which means that they have a finite capacity to accumulate and hold varnish products. However, there is an important difference in how each does this. Due to the manufacturing process resulting in a more highly saturated molecule, Group II oils have less varnish-retention capacity than Group I oils. As such, Group II oils allow varnish deposits within a system to occur with a lower overall volume of the material present.

System Cleanliness

When a new charge of turbine oil is installed, it is vital that the system be clean and free of varnish. A common problem is that many existing systems are not cleaned prior to the installation of new/replacement oil. As mentioned previously, turbine oil has a natural design property that allows it to hold and accumulate varnish. In addition, existing system sludge and varnish that have adhered to surfaces within a turbine oil system are not readily dislodged with a system flush. As a result, when new, clean oil encounters this existing varnish within a system, it begins to chemically react with the varnish and remove this material from the walls, causing the new oil to approach a point of saturation.

Figure 3. Varnish deposits were
found within this system.

Within a relatively short period of time, this “chemical cleaning” phenomenon can render the benefits of a new oil change moot in terms of oil performance and design. In other words, the removal of system varnish may reduce the new oil to a “failed oil” status not long after it is placed in service.

The same condition occurs after a varnish-saturated oil is cleaned of varnish residue, but the cleaning is stopped prior to the system itself becoming clean. The newly cleaned oil will again accumulate varnish materials from the system to once again approach saturation levels. Remember, varnish acts as a catalyst to speed oil and additive degradation. As such, operating with varnish within the oil allows new varnish to form more quickly and shortens the service life of the oil.

Complications/Variations

The consequences of accumulated varnish within a turbine system can include power de-rating and damage to the operating equipment. When observed problems begin to occur, the concentration of varnish within the oil or system can vary greatly. Factors such as system design, variations in the system operating temperature and fluctuations in the system operating conditions all affect varnish formation.

Systems that use turbine oil as control oil are highly susceptible to issues. The control systems include tight orifices located in lower temperature regions. These conditions allow hot, saturated oil to accumulate deposits at these important system locations.

The choice of oil also impacts the rate of varnish generation and accumulation, as some oils are more prone to varnish drop-out than others. Figure 4 shows two samples with similar laboratory settling times. While these oils have a highly similar visual appearance, they have dramatically differing levels of varnish load, which is related to the influence of oil additives, base oil and the chosen formulation.

Figure 4. Different oil formulations can have very different
varnish conditions but appear highly similar.
(Courtesy Dave Wooton, Wooton Consulting)

Oils from different manufacturers are known to have different additives and base oils. Depending on the in-service operations, their differences can influence the severity of a developing varnish issue. Because these oil design variations are considered proprietary information by the lubricant manufacturers, the consumer of the oil is unlikely to be able to determine which oil formulation is least likely to cause varnish problems.

When system contaminants mix with the oil in service and further degrade it, the design properties such as water separation, foaming and the oil oxidation rate may be greatly compromised. As system design and operating conditions also vary, their impact should be considered as it relates to the select formula as well. This parameter of additive chemistry adds to existing varnish challenges for both oil performance and service life.

Laboratory Testing

The lubricant condition-monitoring community has developed a laboratory test (ASTM D7843) to assess the degree of accumulated varnish load within in-service oil. This Membrane Patch Colorimetry (MPC) test measures the overall load of varnish type material in the oil sample and includes a three-day settling period to allow varnish material to agglomerate within the oil, which is cooling from its operating temperature.

The oil is then filtered through a 0.45-micron cellulose patch with the aid of a solvent. Varnish material collects and deposits on the patch. The patch is checked for color, which is influenced by the volume of material deposited. A dark brown color is visible when more varnish from the fluid is on the patch surface.

Figure 5. The MPC test measurement of the sample on the
left was 24, while the sample on the right measured 156.
(Courtesy Dave Wooton, Wooton Counsulting)

Figure 5 shows side-by-side examples of a split sample of turbine oil that was allowed to sit for a two-week settling time under controlled conditions. The sample on the left was stored in the dark, while the sample on the right was left in the sun. The contribution of the sun is the difference in these samples, which have different colors and very different varnish loads.

Alarm Limits and Criteria

The lubricant test community is currently using various versions of the color patch test to assess the volume of varnish within oil and the likelihood of damaging deposits occurring. Unfortunately, the test variations in use may scale the color differently and provide differing warning and alarm limits. These differences can lead to significant confusion in the marketplace.

In addition, current alarm limits and action criteria focus on the effect of varnish accumulation on lubricated machinery. This approach discounts the impact of varnish on the design and function of the oil as well as the potential effect of this material on other oil failure modes.

3	days of settling is included in a Membrane Patch Colorimetry (MPC) test to allow varnish material to agglomerate within the oil, which is cooling from its operating temperature.

A more fundamental approach to setting alarm and action limits that includes the impact of varnish on the oil’s performance is needed. The criteria should consider when the oil has lost its design performance, and these performance failure modes should be the point of initial action.

A temperature limit of oil saturation could become an important criterion. This could be measured by the patch test but at lower limits than those presently used in order to avoid machinery issues. This approach could then retain the present criteria as a higher severity warning for varnish and separate criteria for its potential challenge to machine operation.

Mitigation

Since oil that is in operation at a fully saturated level can be expected to leave varnish deposits, mitigation strategies to manage this condition should be directed at keeping varnish levels at a concentration where deposits would not be expected to form. The following are viable preventive maintenance strategies that have been demonstrated to benefit the system oil condition or varnish saturation level:

Partial or Full Oil Changes

As new oil does not have any retained varnish products, it would not be expected to cause new deposits when added to the system. However, the benefit of this method is severely limited by the quantity of varnish deposits within the system. When new (or newly cleaned) oil is placed in service, its inherent design results in cleaning the existing system varnish, which then goes into the oil. After this has occurred, the oil can again become saturated, and new varnish deposits can commence once saturation levels have been reached.

A secondary problem can develop from this mitigation strategy if varnish is removed from a less harmful area and then re-deposited in more undesirable locations. Another drawback in making frequent oil additions including full oil replacement involves the expense, as large volumes of oil can be costly.

While this approach could be beneficial if implemented in a manner that keeps the oil in a less than saturated condition, managing this would require frequent laboratory tests to ensure the oil condition. It is also questionable whether oil consumers would be sufficiently sensitive to the rate of varnish accumulation or change in the new oil to properly implement this method. However, it would produce a net benefit if performed periodically, as the cleanliness of the system in terms of existing varnish deposits can be improved with time.

Filtration with Cellulose Media

The best time to filter varnish material retained within oil is when the oil is at an ambient temperature for a few days. This allows the varnish to agglomerate and be collected by the filter material. Filter replacement is a must if this strategy is employed, as varnish material removed from the oil at ambient temperature returns to solution if the filter is not replaced prior to returning the oil to the higher operating temperature. This is due to the greater solvency of the oil at the higher operating temperature.

The primary limitation of this approach is that the filtration is limited to the reservoir oil and cannot be expected to reduce the volume of varnish within the main turbine system. When the oil returns to service, its inherent design is as a solvent, thus the results are removal of system varnish. Once again, due to existing system deposits, a saturation of the operating oil can reoccur.

In addition, varnish can migrate from a less harmful area to an undesirable location. The overall cost of this strategy can also be expensive, as frequent filter replacements could be required to remove system varnish from the varnish-laden filters. However, this method does produce a net benefit when performed periodically, and the cleanliness of the system in terms of varnish deposits can be improved.

System Chemical Cleaning

This method is the quickest way to improve system cleanliness and allow the oil to function as it was designed. While a clean system will extend the useful service of the new replacement oil, it cannot be expected to prevent reoccurrence of varnish. Its cost to implement can also be high.

Ion Filtration

With ion filtration, oil is processed through resin beads, which chemically attract the varnish component and remove it from the oil. This cleaning can occur at operating temperature. Ion filtration takes advantage of the oil’s design to slowly clean and remove existing varnish from the system as the oil is in service. With time, this process produces both a clean system and clean oil.

Conclusion

Mitigation strategies of ambient temperature filtration followed by filter replacement or installation of new oils can be used to manage varnish in systems if carefully employed. Of course, these strategies will carry the cost of additional oil and filter purchases. Regular laboratory testing also would be needed to manage these strategies and to monitor their effectiveness.

The introduction of Group II base oils as a fundamental component of turbine oils has not caused the varnish issues that plants are currently encountering, although their solvency and capacity to hold varnish were contributing factors. The change to a Group II base oil component has reduced the capacity of the fluid to retain varnish materials. Additional contributors include the formulation of the oil, the system design, the operating conditions and how much existing varnish is within the system.

81%	of lubrication professionals have experienced problems caused by oil degradation products such as varnish and oxidation, according to a recent poll at machinerylubrication.com

A primary culprit of varnish problems occurring within industry can be directly attributed to the system cleanliness in terms of residual varnish deposits. The key to long-term varnish mitigation is in establishing a system free of varnish and then continuing a process that maintains both the oil and system in this condition. Ion filtration has been demonstrated to create these conditions, although once the system is clean, frequent oil additions or filter replacements may also be useful.

While the current industry focus regarding varnish has been on turbines, the same base oils and formulations are used for compressor, circulating and large motor/gearcase applications. Likewise, the same degradation mechanisms of the oil and additives would be present with subsequent varnish accumulations expected to occur. Such varnish deposits may be found on bearing and gear surfaces as well. Although the consequences of this accumulation and stress on oil properties have not been discussed, sensitivity to varnish should also be applied to these applications.

Alarm and action limits should be established to ensure system and oil cleanliness. This approach is challenged by long-standing plant operating expectations and experiences where varnish sensitivity was not required. The existing belief that there is an acceptable quantity of varnish within either the oil or system and that it is of no consequence must be overcome. Low action and alarm criteria should be set to protect the design and performance of the oil. In other words, a no-tolerance approach to varnish is required.

The Importance of Dirt-Holding Capacity in Oil Filters

Article extract from ReliaPlant newsletter:
http://www.machinerylubrication.com/Read/29114/dirt-holding-capacity

The enemy to any lubricated machine is particle contamination. In a perfect world, machines would be sealed up to block the ingression of particles before any problems occur, but unfortunately this isn’t the case. We live in a dirty environment. Particles exist everywhere, and lubricated components are constantly under attack from them. Whether the particles are ingested by poor-quality breathers or dirty oil from a recent top-up, the question remains what can be done to get rid of them. The obvious solution is filtration.

Filters can extend the life of machines by removing harmful particles before they can cause surface degradation of the lubricated components. There are two common types of filters: surface or membrane filters and depth filters. Surface filters simply trap particles on the surface or face of the filter. Depth filters allow the oil to flow throughout the body or depth of the filter and trap particles throughout the media. Perhaps the most crucial attribute of any filter is the ability to trap and hold dirt.

60%	of Lube-Tips subscribers use surface or membrane oil filters most frequently at their plant

Each filter has a specific pore size. This is the size of the openings within the media through which the oil and particles can pass. As the pore size gets smaller and smaller, the differential pressure across the media begins to increase as well. This differential pressure can lead to a condition in which the bypass or cracking pressure of the filter is reached, allowing oil to flow through virtually unfiltered. Also, if the pressure becomes too great, it can cause the actual filter media to burst.

Once particles are captured, it becomes a measure of how well the filter can retain them. This is known as the dirt-holding capacity of the filter. Several factors contribute to how well filters hold the contaminants they catch. We’ve discussed the pore size of the filters, but pore density is equally important. Pore density can be described as the number of pores in a section of the filter. This is also known as the porosity of the filter. As pore size goes down, to maintain a low differential pressure across the media, the pore density must go up to account for the volume of oil in contact with the surface. Thus, filter depth and size also affect the dirt-holding capacity.

Cellulose (Wood Pulp) Filter Media

Another thing to keep in mind when selecting filters is the material the media is composed of. This not only has an effect on the longevity of the filter and its adaptability to its environment but also its dirt-holding capacity. Two common types of filter media are cellulose and synthetics. Cellulose is comprised of wood pulp. These types of filter media have a large fiber size and a less consistent pore size throughout the entire filter. Cellulose has the advantage of being able to absorb some water from the oil it is filtering. Cellulose filters tend to fail quicker in acidic environments as well as in high-temperature applications.

Synthetic filter media generally have a higher dirt-holding capacity than cellulose. This is due in part to their more consistent pore size throughout the media. Synthetic fibers are smaller than cellulose fibers, so they can be packed tighter together, creating more pores in which to trap and hold particles. Synthetic fibers also perform better in the harsh environments that tend to destroy cellulose filters.

Fiberglass Filter Media

In examining the technical sheets of filters, you may have seen a filter’s beta rating. This describes how efficient the filter is at removing particles. There also may have been a value for the dirt-holding capacity. This value is obtained through a test known as ISO 16889 or the multi-pass test. In this standard test, a filter is put into a circuit that is filled with oil. The oil circulates through the filter. A set amount of sized particles is then released into the oil to test the filter’s ability to capture them. A particle counter before and after the filter measures the difference in particles. The results of this test will allow you to see how well or poorly a filter performs against different particle sizes.

Keep these things in mind when selecting the next filter to clean your oil and protect your expensive machinery. Check the filter’s beta rating and pore size. Obviously, there is a big difference between a 40-micron filter and a 3-micron filter when you are talking about the size of particles allowed downstream. Also, whenever available, verify the results of the ISO 16889 multi-pass test. This not only will show you the efficiency of the filter, but also how well it is able to retain the particles it removes from the circulating oil.

Fiberglass vs. Cellulose

Some filter manufacturers don’t show the results of this test as it pertains to the dirt-holding capacity of the filter, but by pressuring them and demanding to see the results, you can make the best decision for you and your machines. If they balk at the idea of providing the test results, there are labs across the country that can run the ISO 16889 test on the filter to give you the results. This is more expensive for the end user, but it offers the peace of mind that you have the right filters for your applications.

Prolonging Filter Service Life

Selecting the proper filter with a high dirt-holding capacity is only half the battle. You also must ensure these filters are put into use the right way. Filters can be expensive, so naturally you want to prolong the life of the filter to cut down on the costs associated with changing them.

Double the size of the filter and you can triple the service life (dirt-holding capacity). Reference Pall Corporation

One of the easiest ways to prolong the filter change-out interval is by simply oversizing the filter. As you can see in the chart above, by doubling the surface area of a filter, you can expect three times the life from it.

There are different methods to oversizing filters. The most obvious is by increasing the physical size of the filters you are using. This is somewhat costly, as equipment modification is required to fit a larger filter in the lines. For some equipment where space is limited, this may not even be feasible. That is when you should start looking at putting filters in parallel.

By placing multiple filters in parallel, you double the surface area in contact with the oil, thereby reducing the face velocity (the pressure of the oil on the surface of the filter media), and thus extend the life of the filter. This means less filter changes and the ability to capture more particles between change-outs.

If the equipment won’t permit the extra piping to put in a parallel circuit, there are systems that stack filters one on top of another to increase the overall length of the media, again allowing for the decrease in pressure the media is experiencing.

Machinery Lubrication (10/2012)

About the Author

Wes Cash

Wes Cash is a senior technical consultant with Noria Corporation, focusing on machinery lubrication and maintenance in support of Noria's Lubrication Program Development (LPD). He holds a ... Read More

How Oil Quality Changes During Startup

Equipment manufacturers generally provide guidelines on how oil should be maintained for reliable operation. Because components have little tolerance for contamination or oxidation, frequent oil sampling and monitoring are performed while the equipment is online in order to keep the unit operating without any issues. However, many times little attention is paid to the oil quality when the equipment is shut down for a maintenance outage or on standby. This can eventually affect the unit’s reliability.

For instance, when a steam turbine is down for prolonged periods or for a short three-week maintenance outage, the consequences of not having hot, circulating oil running through the system is usually not considered. In fact, the oil quality when placing a turbine on turning gear or during startup is often not the same as when the unit came offline.

Prolonged exposure to water can
rust a control system.

Typical turbine bearings are designed for fluid-film lubrication. Most fluid-film bearings are intended for hydrodynamic lubrication. This means an oil wedge is formed in a hydrodynamic bearing to develop separation and maintain an oil film between the rotor and bearing. The film thickness is a function of rotor speed, load and oil viscosity. Under fluid-film conditions, an increase in viscosity or speed increases the oil film thickness, while an increase in load or decrease in rotor speed reduces the oil film thickness.

In developing an oil film, the bearing surface geometry and rotor surface are just as important as rotor speed, load and oil viscosity. To establish a stable oil wedge and fluid film between the surfaces, the rotor and bearing profiles must be perpendicular. If either or both surfaces become damaged by large particles being pushed through the bearing, the ability to form an oil wedge is diminished, resulting in a thinner oil film thickness. Reducing the oil film thickness increases the susceptibility of additional damage or producing a rub during coastdown or startup.

The congealed mass shown above is an example of particulate matter and
degraded oil buildup that can accumulate in a turbine control servo.
Left unattended, this condition could eventually cause poor
turbine control response and accelerate equipment wear.

When the turbine rotor is at normal operating conditions, the bearing is in hydrodynamic lubrication conditions. However, when a turbine rotor is on turning gear or beginning to roll at slower speeds, the journal bearing is in boundary lubrication conditions. These conditions are generally indicated by some metallic friction and wear.


Very high coefficients of friction may also be reached. At this point, the oil film thickness between the bearing and the turbine rotor will be at its minimum. The film thickness will increase as either the speed is increased, the lubricant viscosity is increased, the load is decreased or the geometric shapes of the journal and bearing surfaces relative to each other are improved. If the surface becomes rougher (the bearing surface becomes damaged), then the risk of rotor and bearing surface contact increases. This relationship between the surface roughness and the film thickness is important in the consideration of hydrodynamic lubrication of a turbine bearing.














 These images show the buildup of particulate in a turbine oil reservoir that is cleaned periodically. Consider the type of buildup that could occur over the life of the plant.

A major concern with rough surfaces, including gouges or grooves around the journal or along a Babbitt surface, is that they allow high-pressure lube oil to flow away from the thinnest film areas. This permits increased contact and shear forces on the Babbitt than would occur with smooth, concentric and round journals on a smoothly bored Babbitt surface bearing. This is why surfaces that appear to have minimal damage can still cause bearing failure during startup or slow-speed operation before a fully developed hydrodynamic film with a normal film thickness exists.

During a plant startup, when a turbine is on turning gear or at lower speeds, the lubrication system may supply lube oil with slugs of particulate matter to the journal and thrust bearings. This is especially damaging to journal bearings because they carry the applied load forces that force the journals into contact with the bearing surface, thus providing a very thin oil film. This form of lubrication is known as boundary lubrication. Because only a very thin oil film exists between the journal and bearing surface, and many of the particles in the oil are larger than this oil film thickness, the bearing surface can be scored as particulate becomes imbedded in the surface of the Babbitt. In some cases, the particulate can score the journal, requiring it to be remachined and/or honed.

Water Contamination

Water contamination in a lubricating or control system is particularly undesirable because it tends to form an emulsion with the oil. Elevated water content in an oil system can also affect lubricity and induce corrosion. When a lubrication or control system is shut down, the normally wetted regions, such as those in the lube oil drain pipes, become exposed to air. Enlarging the surface area of carbon steel that is subject to ambient conditions increases the amount of internal corrosion (rust) a system develops.

While a unit is operating, the amount of water in the lubricating or control system is normally maintained within the manufacturer’s specification by the plant’s oil-conditioning system. These systems often contain some type of demulsifying agent to remove water. Even if the water content is well above normally acceptable standards, the steel surfaces are usually kept wetted with oil, and corrosion (rust) is limited. However, when the turbine is shut down for weeks or months, water will generally separate from the oil in the pipes and components where the oil resides. If water separation occurs, it can corrode the equipment, support microbiological growth and/or affect the functioning of the control system. Additionally, when drained, large portions of the system normally filled with oil become exposed to the environment (air and oxygen). Obviously, the longer the duration a turbine lubrication system remains secured, the more time the equipment has to oxidize.

Particle Contamination

This orifice plug from a boiler feed
pump turbine control has deposits
covering the orifice holes.

Particle contamination not only can cause equipment to wear, but it also clogs lubrication ports, in-line filters and control systems. During operation, the parameters used to monitor oil tend to remain stable, but when the system that is designed to maintain lubrication and keep piping and hardware clear is secured, the rate of oxidation on the exposed surfaces increases. Then, when the unit is returned to service, the newly formed corrosion (rust) on any exposed piping or surfaces often is shaken loose or washed away with the restarted oil flow. Furthermore, where there are pockets in which stagnant oil may have settled, a slug of particulate and coagulating oil can easily form. When the oil flow is restarted, this particulate matter is easily pulled into the lubrication flow streams and circulated throughout the lubrication system.



One substantial area of concern is the control system. Because of the system’s complexity and low-flow velocity within the control piping, the system acts as a collection point for particulate.

Biological Growth

When a lubrication system is secured for prolonged periods of time, biological growth can occur. Low-flow areas can collect a tremendous amount of sludge over the years. With this amount of growth, a sudden change in the lubricating system’s temperature, such as that which occurs when returning the system to service, can result in the biological growth dying off and the remains being pushed through the system.

Biological growth, particulate and separated lubricant additives have
collected on this pump (above left). The lube oil cooler on the
right has biological growth and adhered lubricant additives.

Cleanliness Codes

Most plants have equipment monitoring programs that define lubricant property limits. These limits are usually established for normal operating conditions. One of the parameters typically monitored is particulate levels. The International Organization for Standardization (ISO) has developed a method (ISO 4406) for quantifying the level of particle contamination. The values gathered in a particle count test identify the number of particles in a given volume of fluid that are above a specific size range, which is generally set at 4 microns, 6 microns and 14 microns. The data is normally presented in a format such as 17/15/13, which provides a numeric range value representing the measured quantity of particles greater than 4 microns, 6 microns and 14 microns, respectively.

Case Studies

In a recent turbine outage, the lubrication system was placed into operation, and the main turbine was placed on turning gear. While the system was operating, an auxiliary filtration skid was connected to the main turbine reservoir to run in parallel with the normal filtration system. The skid had dual 7-micron filters and processed the main turbine reservoir four times per hour. An oil sample recorder pulled samples at 20-minute increments from the center of the turbine oil reservoir and then documented 31 hours of results from the mesh blockage particle counter.

Figure 1. The results from a mesh blockage particle counter revealed that a large amount
of contaminants were released into the lubrication system after 12 hours of operation.

As Figure 1 indicates, after approximately 12 hours in operation, a large slug of contaminants must have released into the system, causing the need to change filters. At that point, a decision was made to reduce the filter size and continue. Once the turbine was rolled, the auxiliary filtration unit was secured. Inspection of the last set of filters revealed a significant collection of particulate captured within the filters.

In another example, a filtration skid with a particle counter was tied into a turbine reservoir during the plant’s startup. This power plant normally only operates during peak summer months in the southern part of the United States, leaving it shut down for at least six months out of the year. The particle counter recorded main turbine reservoir contaminant levels above 4, 6 and 14 microns. Figure 2 illustrates the change in particulate levels from the time the turbine was on turning gear until the unit was synchronized to the power grid.

Figure 2. This graph illustrates the changes in oil particulate during the startup
of a turbine. The dash lines provide the lSO 4406 “alert” level for specific particle sizes.

Notice when the turbine rolled off turning gear and increased its speed to 2,400 revolutions per minute for thermal soaking, a large burst of particulate was released into the lubrication system. This caused all three particle levels to increase above the normal operating limits and remain high for more than two hours. Added filtration was able to bring the particle levels down to acceptable limits, but when the turbine speed was increased to synchronize the generator to the power grid, another spike occurred.

Plants generally do not monitor particle levels as equipment is placed back into service. When a turbine is at normal operating speed, the minimum oil film thickness between the turbine rotor and the bearing surfaces is in the order of 0.002 inches for journal diameters from 8 to 16 inches. The minimum film thickness increases to 0.010 inches for the largest journal bearings with 30-inch diameters. However, when the turbine is on turning gear, this oil film thickness is only a few microns thick at best.

As the speed increases, so does the film thickness between the rotor and bearings. If a large mass of particulate gets into a journal bearing when the film thickness is only microns thick, the particulate matter can scar or damage the journal and/or bearing profile, which in turn affects the fluid dynamics within the bearing. This often leads to overheated bearings and possibly to bearing failure.

To control particulate matter, it is better to use filter element sizes than ISO charts, since ISO charts allow a few large particles, which can lead to journal bearing failure.

Understanding what is occurring provides the best way to identify and assess risk. Once a risk is identified, actions can be taken, consequences evaluated, mitigations and contingencies developed, and an implementation plan pursued.

There are many ways to reduce risks when bringing large equipment back into service. A review of vibration data and other parameters can tell a lot about how the equipment performs when going from cold to normal operating conditions. It also will inform you of what is needed to extend the health of the equipment or increase the operating efficiency.

Connecting a kidney-loop filtration system to a tank or reservoir can help
reduce the risks when bringing equipment back into service.

Perhaps the most versatile and cost-effective method to help reduce the risk to equipment is to have a kidney-loop filtration system available. This type of system can be connected to a tank or reservoir to support bringing the equipment back into service.

The filtration unit should be sized to process the contents of the tank or reservoir several times per hour. In addition, the unit can be equipped with a cooler for summer months when thermal loads on the plant limit equipment operation. Along with filtering and cooling, a kidney-loop system can include a dehydrator, which provides an excellent way to extract water from the oil before placing the equipment on turning gear. This will reduce the amount of water that gets pushed through high-pressure differential regions of the oil film in the journal bearing and reduce the risk or amount of flashing, which causes damage and erosion of Babbitted and non-Babbitted surfaces.

Keep in mind that the expense of an auxiliary filtration skid can be quickly offset by a reduction in maintenance costs. In fact, the cost of replacing a damaged bearing or by keeping plant equipment running during peak summer months could easily justify reducing the risk of repeat failures. For example, a 10-percent power reduction at a nuclear plant during peak summer temperatures would pay for auxiliary filtration systems on most challenged equipment within days.

.

Machinery Lubrication (10/2013)

Anatomy of an Oil Filter

Article extract from ReliaPlant newsletter:
http://www.machinerylubrication.com/Read/29396/oil-filter-anatomy

This is the second part of a series of “anatomy” lessons within Machinery Lubrication. In this issue, the oil filter will be examined to uncover its functional and performance characteristics. Several other related topics will also be discussed, including best practices for oil filter usage, possible filter failure modes, factors for proper filter selection and how to maintain an installed filter.

By definition, an oil filter’s main role is to cleanse oil from destructive contaminants within a machine such as an engine, transmission, hydraulic system and other oil-dependent systems. In the case of automotive oil filters, canister-type filters are the most common. This filter configuration was most likely responsible for the advanced performance of oil filtration technology.

In 1922, Ernest Sweetland invented the first oil filter device for automobiles. It was named the “Purolator,” which was short for “pure oil later.” The spin-on filters common in today’s automotive industry were introduced in the 1950s and were virtually a standard by the early 1970s.

Aside from the automotive industry, oil filtration is an integral part of equipment within a wide variety of industries, including aerospace, power generation, oil refining, manufacturing, mining, etc. Although most current oil filter designs come in canister or cartridge types, several variations in size, filter media, dirt-holding capacities and flow arrangements are available. For this reason, it is important that filters and filtration systems are selected to meet the needs of the application and with cost, performance, ease of use and environmental conditions in mind.

Oil Filter Types

Oil filters can be characterized by the method in which the contaminants are filtered or the method in which the oil flows through the housing. One technique used to control contamination in filters is through surface-type media. This is the type of filter used in automobiles. In depth-type filters, the filter media are designed to hold much higher levels of contamination and provide a more circuitous path for lubricant contaminants to become trapped.



Other possible contamination control methods include magnetic and centrifugal filtration. Magnetic filtration utilizes rare-earth magnets or electromagnets to attract and collect ferrous particles as the oil passes through a magnetic flux region. Centrifugal filtration works by integrating a rapidly rotating cylinder to produce a centrifugal force for contamination separation from the oil.

Oil filters can also be categorized by the oil flow design. As its name implies, a full-flow filter will draw all of the oil through the filter media. On the other hand, a bypass filter only requires a fraction of the oil flow for sufficient flow rates within the system. The application’s oil flow and contamination control requirements will determine which design is the best option. Another alternative is the duplex filter system, which contains two side-by-side filters in parallel to allow one of the filters to be replaced during uninterrupted operation.

With typical canister-type filters, it is standard for oil to flow from the outside in. This means that the oil travels through the cylindrical filter media from the outward-facing surface into the inner core. However, in some cases the flow direction is reversed, with the oil coming into the filter through the core and pushed outward through a unique pleat design. This is intended to improve flow handling and distribution as well as reduce filter element size.

Filtration Mechanisms and Filter Media

A filter’s primary function is to remove and retain contaminants as oil flows through the porous component called the media. The media operate under several types of filtration mechanisms, including:

• Direct Interception and Depth Entrapment – Particle blockage on the media due to the particles being larger than the taken passages within the media.
• Adsorption – The electrostatic or molecular attraction of particles between the particles and the media.
• Inertial Impaction – Particles are impacted onto the filter media by inertia and held there by adsorption as the oil flows around.
• Brownian Movement – This causes particles smaller than 1 micron to move irrespectively of the fluid flow and results in the particles being adsorbed by media in close proximity. It is much less prevalent, especially in viscous fluids.
• Gravitation Effects – These allow much larger particles to settle away from fluid flow regions when there is low flow.

In addition, filter media can be designed to capture particles through two distinct methods:

• Surface Retention – Contaminants are held at the surface of the media. This provides an opportunity for the contaminant to become trapped as it comes in contact with the media surface.
• Depth Retention – Contaminants are held either at the surface of the media or within the labyrinth of passages within the “depth” of the filter media. This creates several opportunities for contaminants to become trapped.

The graph below shows how depth-type filtration is more efficient in capturing smaller particles when compared to surface-type filters. This can be attributed to the deeper media providing more chances for the particles to be trapped along with the adsorptive and Brownian movement effects being more predominant in depth-type filters. While these characteristics are beneficial, depth-type filters tend to have higher differential pressure across the media as a result of the increased flow restriction from the deeper filter media.

Particle size retention characteristics of
depth-type and surface-type filter media.

Filter Media Types and Dirt-Holding Capacity

In the September-October 2012 issue of Machinery Lubrication, Wes Cash explained how the porosity of the filter media plays a role in how well the filter can retain captured particles. This is known as the dirt-holding capacity. As pore size goes down, to maintain a low differential pressure across the media, the pore density must go up to account for the oil volume in contact with the surface. The filter depth and size also influence the dirt-holding capacity. Another factor is the filter media material. There are three primary types of filter media:

1. Cellulose - Comprised of wood pulp with large fibers and an inconsistent pore size.
2. Fiberglass (Synthetic) - Comprised of smaller, man-made glass fibers with a more consistent pore size.
3. Composite - Comprised of a combination of cellulose and fiberglass material.

Cellulose media are advantageous because they can absorb some water contamination. However, these types of media tend to fail more rapidly than synthetic media in acidic and harsh oil conditions. Nevertheless, the primary reason synthetic filter media are preferred is their more consistent porosity and smaller fiber size, which contributes to higher dirt-holding capacity and longevity of the filter.

This example of a depth-type filter has an element that requires
oil to pass through 114 millimeters of filter media
for maximum particle filtration. (Courtesy Triple R)

Understanding the Beta Rating

Oil filters are rated by a technique called the beta rating. In his Machinery Lubrication article “Understanding Filter Efficiency and Beta Ratios,” Jeremy Wright explained the methodology behind the beta rating in more detail. In short, the beta ratio is calculated by dividing the number of particles larger than a certain size upstream of the filter by the number of particles of the same size downstream of the filter. Every filter will have multiple beta ratios for different particle size limits such as 2, 5 or 10 microns.

Best Practices for Oil Filter Usage

Storage - Filters can fail long before they are to be used for their intended purpose. Therefore, proper filter storage and handling are essential. Ensure filters are kept clean, cool and dry, and always follow the first-in/first-out rule.

Installation - Even if a filter installation seems simple and routine, refer to the manufacturer’s recommendations for proper procedures. A classic mistake is over-tightening. Most recommendations suggest that a three-quarter turn after seal contact is optimal. Over- or under-tightening can inhibit the seal’s longevity and effectiveness. Confirm that connections, seals and ducts are fitted appropriately and are free of contaminants.

Avoiding Pre-fill - In most cases, you do not want to pre-fill your oil filters before installation. In diesel engines, it is recommended that a pre-lube system be installed instead in order to counteract changes from dry-start conditions.

Choosing Correctly - Many filters and filter housings are designed to be interchangeable, so just because a particular filter fits doesn’t mean it is the correct filter. Make sure each filter is replaced with the right filter. This may not necessarily be the one found on the machine, as an incorrect filter might have been used during the last filter change.

Training - Proper training must be conducted for all personnel involved with changing filters. Remember, a task that seems straightforward to most people may not be for a new employee.

Filter Failure Modes

Channeling - During high differential pressures, filter media passages can enlarge to a point where unfiltered oil can pass through without an efficient contaminant capture. In addition, any particles that were previously contained within the filter in line with the enlarged passage may now be set free.
Fatigue Cracks - In cyclic flow conditions, cracks can form within the filter media, allowing a breach of oil to pass through unfiltered.

Media Migration - Media fibers can deteriorate and produce new contaminants made up of filter material. This may be caused by improper placement of the filter housing or an inadequate fitting of the filter, which can generate damaging vibrations. Embrittlement from incompatible oils or extremely high differential pressures can also result in media disintegration.

Plugging - During operation, filter media can become fully plugged by exceeding the dirt-holding capacity. Plugging can occur prematurely if excessive moisture, coolant or oxidative products like sludge are present.

61%	of lubrication professionals say filter plugging is the failure mode seen most frequently in oil filters at their plant based on a recent survey at machinerylubrication.com

Factors for Proper Oil Filter Selection

Structural Integrity - Arguably the most critical factor, structural integrity relates to a filter’s ability to prevent the passage of oil through an unfiltered flow path. The International Organization for Standardization (ISO) has established procedures for testing fabrication integrity, material compatibility, end load and flow fatigue. These tests can reveal defects such as improper sealing of seams and end caps or breaks in the media from high-flow conditions, as well as the effects of high temperatures on the filter element.

Contamination (Dirt-Holding) Capacity - This refers to the amount of contaminants that can be loaded onto the filter before the filter’s efficiency is limited.

Pressure Loss - This involves the overall differential pressure lost from the filter’s placement on the system. The pressure loss will be influenced by the filter media’s porosity and surface area.

Particle Capture Efficiency - This is the overall effectiveness of the filtration mechanisms within the filter media to extract and retain contaminants from the oil.

System/Environment - The characteristics of the system and environment in which the filter will be installed must be considered, including the contamination expectations, flow rates, location, vibration, etc.

Maintaining Installed Filters

The best way to prevent filters from reaching their dirt-holding capacity is to avoid contaminants in the system from the beginning. The fewer external contaminants that ingress, the fewer contaminants that are generated internally (particles produce particles). Use the following guidelines to maintain installed filters:

• Ensure proper breathers are installed to prevent contaminants and moisture from entering the system.
• Keep seals and cylinders clean and dry by using appropriate wipers and boots.
• Select the appropriate oil grade and additive package to counter contaminant ingression and internal friction.

Analyzing the Filter

A filter not only is a trap for the machine’s undesirables but also a concentration of clues as to what’s occurring within the machine. Particles within the oil may be so highly diluted that practical analysis can become a daunting challenge. However, the particles trapped in the filter may be so plentiful that they can be easily visible to the naked eye.

Metal contaminants are a primary indication of an issue within the machine. Although some amount of metal contaminants can be expected, an unusual amount should be recognized by trending the filter’s visual appearance after each oil change. Cutting open the filter and suspending a strong magnet over it can aid in pulling out the metal contaminants to more easily distinguish them.

If the machine is suspected to have an issue, the filter should not be discarded, as this would be similar to throwing away key pieces of evidence. Maintain the filter in the same condition as when it was removed and have it analyzed by the manufacturer or a laboratory.

Filter Disposal

Oil filters are not designed to be dumped into any wastebasket. Increasing regulations by the Environmental Protection Agency dictate proper filter disposal. While each type of oil filter may have its own requirements, common practices include oil draining, crushing or incinerating the filter. Many disposal services or filter distribution centers will accept used oil filters at little or no cost.

References

Fitch, E.C., An encyclopedia of contamination control, 1980s
Fitch, E.C., “How to Select Fluid Power Filters,” The BFPR Journal, 1979, 12, 3, 197-201
Erosion Control, Equipment World Magazine, December 1991
Filtration Manual, PTI Technologies Inc., 1990
Pall Corporation, Ultipleat SRT Filter Brochure, Nov. 2007
Triple R Oil Cleaning Products, Product Brochure, 2013

Machinery Lubrication (6/2013)

About the Author

Bennett Fitch

  Bennett Fitch is a technical consultant with Noria Corporation. He is a mechanical engineer who holds a Machine Lubricant Analyst (MLA) Level III certification and a Machine Lubrication ... Read More