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

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

Tips for Better Process Pump Lubrication

Article extract from Machinery Lubrication newsletter:
http://www.machinerylubrication.com/Read/29280/process-pump-lubrication

The overwhelming majority of process pumps in industry comply with the standards of the American National Standards Institute (ANSI) or the American Petroleum Industry (API). However, neither of these two standard categories mandates any one particular type of lubrication. Grease lubrication, as well as lubrication by liquid oil or atomized oil (oil mist), or even pressurized pure oil are used in various process pumps. Generally, grease is chosen for ease of lube containment, but it is limited to relatively small ANSI pumps. The larger pumps and virtually all API-style pumps are oil-lubricated, but lube type selection and the designs that apply lube to bearings can vary.

Lubricant types are categorized as either mineral oils or synthetic oils, and they certainly differ in cost. Also, lubricants need to remain relatively clean in service, and lube change intervals must be optimized. In short, important choices and decisions will need to be made. Therefore, guidance from reliability improvement and cost points of view will be necessary.

Oil Rings Interact with Lubricant Viscosities

Viscosity is by far the most important property of lubricants applied to process pump bearings. In general, thicker viscosity oil films will protect rolling-element bearings better than oils with thinner viscosity. For process pumps with rolling-element bearings, ISO Grade 68 (VG 68) lube oils will allow higher operating loads than VG 32. The problem is that oil rings or slinger rings that are optimally designed to apply VG 32 will not work equally well with the more viscous VG 68.

Oil rings typically operate best in an as-designed speed range with closely maintained depth of immersion, ring concentricity, shaft system horizontality and surface roughness of contacting parts. For long life and low frictional losses, different bearings are sometimes best lubricated with different viscosity lubricants. But what if these bearings share the same bearing housing? Reliability-focused pump users will need an optimization strategy, and lube-related knowledge will help.

Figure 1. Oil rings can have a tendency to 
malfunction if they contact stationary
housing parts.

Fortunately, ISO Grade 32 synthetic lubricants exhibit oil film thickness and strength properties close to those of VG 68 mineral oils. Therefore, suitably formulated VG 32 synthetic oils are preferred by reliability professionals for many process pump services.

An excellent point in favor of synthetic VG 32 can also be made for many pump drivers, such as the steam turbine bearing housings shown in Figure 2. The sleeve bearing at the drive end of this small turbine was optimally lubricated with a VG 32 lubricant, whereas the rolling-element bearing at the governor end (the thrust-loaded bearing) would survive longer if VG 68 oil could be applied. Because of their superior properties, VG 32 synthetic lubricants incorporate the viscosity needed for reasonable oil ring performance as well as oil film thickness and tenacity characteristics desired for bearing life extension.

Here are a few general guidelines worth considering:

• Using a mineral oil would generally require oil to be changed every six to 12 months. With a clean, premium-grade synthetic lubricant, you would typically extend oil change intervals to at least 24 months. Incorporating the advanced bearing housing protector seals shown in Figures 3 and 4 and guarding against contaminant entry at breather vents could make 36-month change intervals possible.
• ISO Grade 32 mineral oils are often considered too “thin” for pump bearings. They rarely qualify for long-term, risk-free use in pumps equipped with rolling-element bearings in typical ambient conditions. But simply switching to ISO Grade 68 mineral oils will be risky for bearings that depend on oil rings for lube application.
• Appropriately formulated with the right base stock and with proprietary additives, ISO VG 32 synthetics are quite acceptable from film strength and film thickness points of view. In fact, the performance of some ISO VG 32 synthetics duplicates that of ISO VG 68 mineral oils. These superior ISO VG 32 synthetics excel by simultaneously satisfying the requirements of sleeve and rolling-element bearings.
• Superior synthetics achieve high film strength through proprietary additives, so there can be significant differences in the performance of two lubricants of the same viscosity and base stocks. Only one might be suitable for the highest reliability services.
• The notion that one oil type or viscosity suits all applications is rarely correct. Similarly, no fixed or particular oil ring geometry is ideally suited for all oil types and viscosities. Custom-designed oil rings may be required to work with the thicker oils at certain high shaft peripheral velocities.

Although synthetic lubricants cost more than mineral oils at the point of initial purchase, rigorous and all-encompassing cost justifications will often show relatively short payback periods. Combining extended bearing life and extended drain intervals results in better payback. This is made possible by keeping contaminants away from the lubricant. Therefore, upgrading to the best-available bearing protector seals and implementing plant-wide oil-mist lubrication are two principal strategies adopted by world-class plants.

Protect the Lubricant for Longer Bearing Life

Air and the lubricant take up whatever housing space is not actually used by the bearings. For bearings to survive, solid particles and water intrusion must be avoided. For this reason, proper bearing housing protection seals are essential for keeping the oil clean. Reliability-focused users are mindful of the fact that non-optimized bearing housing protector designs can hurt oil cleanliness by shedding slivers of sealing components.

Keeping the oil clean is the first order of business if extended oil replacement intervals are the goal. In turn, achieving extended oil replacement intervals often makes it economical to use superior-quality synthetic lubricants. In combination, advanced bearing protector seals and synthetic lubricants create an environment conducive to long bearing life. Common sense and statistical evidence point to greatly reduced downtime risk and demonstrable maintenance cost avoidance credits.

Because synthetic lubricants are more expensive than mineral oils, some users cling to mineral oils for their process pumps. They also may employ inadequate bearing housing seals because their only concern is the initial purchase price. Wear-prone seals include lip seals and also certain rotating labyrinth seals. Seals to avoid are those that allow a rotating O-ring to contact the sharp edges of an O-ring groove, or O-ring grooves that are wide enough to prevent such contact but that enable copious amounts of contaminants to enter the bearing housing.

While even small machine manufacturers recognize the need to limit both contaminant ingress and oil leakage, inexpensive lip seals are found in some pumps and drivers to keep initial cost low. Yet lip seals typically last only about 2,000 operating hours (three months). When lip seals are too tight, they cause shaft wear and in some cases lubricant discoloration known as “black oil.” Once lip seals have worn and no longer seal tightly, oil is lost through leakage, or contaminants find their way into bearing housings. This fact is recognized by the API-610 standard for process pumps, which disallows lip seals and calls for either rotating labyrinth-style or contacting face bearing housing protector seals.

Small steam turbines often suffer from steam leakage at both drive and governor-end sealing glands. Each bearing housing is located adjacent to one of these two glands, which contain carbon rings. As soon as the internally split carbon rings start to wear, high-pressure and high-velocity leakage steam finds its way into the bearing housings. Traditional labyrinth seals have proven ineffective in many such cases, and only solidly engineered bearing protector seals are effective in blocking leakage steam intrusion.

Figure 2. This cross-section view shows a small steam turbine driver for process pumps.
(Ref. Worthington-Turbodyne)

The bearing housing protector seal in Figure 3 was designed for steam turbines. It incorporates a small- and large-diameter dynamic O-ring. This bearing protector seal is highly stable and not likely to wobble on the shaft; it is also field-repairable. With sufficient shaft rotational speed, one of the rotating (“dynamic”) O-rings is flung outward and away from the larger O-ring. The larger cross-section O-ring is then free to move axially, and a micro-gap opens up.

Figure 3. This cross-sectioned half-view 
illustrates an advanced bearing housing
protector seal for small steam turbines.
(Ref. AESSEAL Inc.)

When the turbine is stopped, the outer of the two dynamic O-rings will move back to its standstill position. At standstill, the outer O-ring contracts and touches the larger cross-section O-ring. In this design, the larger cross-section O-ring touches a relatively large contoured area. Because contact pressure equals force divided by area, a good design aims for low pressure. In outdated configurations, contact with the sharp edges of an O-ring groove risks O-ring damage, and slivers of O-ring material can end up contaminating the lube oil.

Upgrade to a Better Bearing Environment

Fortunately, concerns as to the time it might take to upgrade to advanced bearing protector seals have been alleviated. Modern products fit in the space previously taken up by lip seals.

In 2009, when a Dutch refinery asked for the installation of the bearing protector seal shown in Figure 3 for one of its steam turbines, no modifications were allowed on the existing equipment. Installation of three bearing protector seals on the first machine had to take place during a scheduled plant shutdown.

Figure 4. A conventional lip seal (top) 
versus a modern rotating labyrinth
bearing housing protector seal
(bottom). (Ref. AESSEAL Inc.)

With no detailed drawings of the bearing housings available, the exact installation geometry could only be finalized after dismantling the small turbine seen in Figure 2. One of the main problems was the short outboard length - less than 0.25 inch was available due to the presence of steam deflectors and oil flingers. But the manufacturer’s engineers were able to modify the advanced design to fit into the existing groove of the original equipment manufacturer’s labyrinth seals. Delivery was made within one week of taking measurements of the steam turbine and bearing housings, and the turbine has been running flawlessly for years.

The point is that highly cost-effective equipment upgrades are possible at hundreds of refineries. However, superior bearing protector products for use in steam turbines must be purposefully developed. Compared with standard products typically used in pumps, the type described here offers important advantages, such as being suitable for high temperatures, incorporating Aflas O-rings as the standard elastomer, providing extra axial clearance to accommodate thermal expansion and utilizing high-temperature graphite gaskets. With these advantages in mind, there should no longer be any reason for water intrusion into the bearing housings of process pumps and small steam turbine drivers at reliability-focused facilities.

When running a pump, you might ultimately achieve an operating temperature that allows a certain thick oil to flow nicely, but what if the initial operating temperature at startup is quite low and the oil will not flow freely? That’s what often happens when someone buys a standard “multi-purpose oil” where a superior synthetic would be a far better choice.

Of course, these and similar issues are avoided with pure oil-mist systems. These systems eliminate much of the human element and are less maintenance-intensive than traditional pumps and drivers lubricated with vulnerable oil rings and constant-level lubricators.

Oil Mist Represents Best Available Technology

As stated previously, thick oils can be quite difficult to apply with the oil rings that are typically supplied with API process pumps. These oils are more easily and reliably applied as an oil mist. Neither oil rings nor constant-level lubricators are used in pumps and drivers connected to plant-wide oil-mist systems.

Figure 5. This chart shows how changes in lube application, oil type and lube viscosity tend to affect percentage reductions in bearing friction. (Ref. E. Villavicencio)

Oil mist is an atomized amount of oil carried or suspended in a volume of pressurized dry air. The oil mist - actually a ratio of one volume of oil suspended or carried in 200,000 volumes of clean, dry air - moves in a piping system. The point of origin is usually a simple mixing valve (the oil-mist generator) connected to a header pipe. Branch lines often feed hundreds of rolling elements in pumps and drivers connected to the header.

Figure 6. This chart illustrates how 
changes in lube application,
oil type and lube viscosity affect
bearing temperature.(Ref. E. Villavicencio)

At standstill, or while on standby, pump and driver bearings are preserved by the surrounding oil mist, which exists in the bearing housing space at a pressure just barely higher than ambient. These pump and driver bearings are lubricated from the time when atomized oil globules join to become larger oil droplets. This combining begins whenever the equipment shafts rotate, which is when small globules get to contact each other and start coating the bearing elements.

There are also plant-wide oil-distribution systems whereby liquid oil (not an oil/air mixture) is pressurized and injected through spray nozzles into the pump bearings. These oil-spray systems are not to be confused with the more economical oil-mist systems. However, both oil-mist and oil-spray applications can take credit for lower frictional losses (see Figures 5 and 6) and should be taken into account when doing cost-justification analyses.

Using High-Film-Strength Synthetic Lubricants

Good lubrication practices include choosing the right oil, taking proper care of it and changing it before bearings are harmed. Improvements in lubricant quality can only be achieved by utilizing oils with superior lubricating properties. These would be premium synthetics.

Yet even among prominent synthetic lubricants, oil performance can vary greatly based on the amount and composition of additives in the oil. For process pump bearing lubrication, at least one company combines synthetic base oils including polyalphaolefin (PAO) and dibasic ester base stocks with advanced additive chemistry to realize greater film strength.

Numerous incidents have been documented where advanced lubrication technology has significantly improved pump reliability. In the majority of cases, advanced lube technology with its often more favorable (lower) coefficient of friction results in reduced bearing operating temperatures.

Micro-cracks in bearing surfaces can cause increased noise and vibration. Suitable high-film-strength oils will fill these micro-cracks. This then lowers noise intensity and reduces vibration severity.

High-film-strength lubricants also lessen the probability of lube oil darkening during the running-in period of bearings with brass or bronze cages. There have been reported instances of high frictional contact during the initial run-in period of the copper-containing material recommended by API-610. If the net axial thrust action on one of the two back-to-back oriented bearings causes it to become unloaded, it may skid.

The risk of lube oils darkening during the run-in period of such pumps is reduced through the use of high-film-strength synthetic lubes. To be fair, this risk could also be reduced by insisting on impeccable installation techniques and the selection of bearings with cages made of advanced high-performance polymers. The API-610 stipulation of using thrust bearings with particular load angles and brass cages represents a compromise, which is especially attractive for plants that place the desire to standardize ahead of failure-avoidance concerns.

Whatever the differential cost of a quart of high-film-strength synthetic, it is insignificant compared to the value of an avoided failure incident on critical, non-spared refinery pumps. Therefore, critically important pumps, pumps in high-temperature service and pumps that have failed more often than others in the plant’s pump population should be lubricated with high-film-strength synthetic oils. Their higher cost is easily justified by four to six times conventional oil replacement (draining) intervals and by keeping the oil free from contamination. Oil contamination is effectively avoided by installing advanced bearing protector seals.

On pumps where a problem is in progress, changing to a superior synthetic is highly recommended. If access to the sump drain is safe when the pump is in service, the present oil can be drained while such pumps are on-line and running. Many superior synthetics are compatible with the oil presently used in a particular pump. Still, compatibility must be verified.

Of course, there are certain pump bearing or lube degradation problems that have nothing to do with the lubricant type. In those instances, nothing will be gained by changing over to better oils.

Lubricants for Oil-Mist Systems

Pure oil-mist lubrication eliminates the need for oil rings or flinger discs. No liquid oil sumps are maintained in the bearing housings, hence the term “dry sump” is often used to describe modern oil-mist lubrication. ISO VG 68 and VG 100 mineral or synthetic oils are used, although properly formulated ISO VG 32 synthetics (but not mineral oils) will serve the majority of pump bearings and also virtually all types of rolling-element bearings in electric motors.

Decades of experience on thousands of pumps and electric motors attest to the viability and cost effectiveness of modern plant-wide oil-mist systems. Typical payback periods when using oil mist on problem pumps have generally been less than one year.

Bearing friction can be reduced by switching to different oils, going with a different lube application method or switching both lube application method and oil type. Five different modifications were closely examined in a cooperative effort involving a multi-national lube oil producer and a prominent bearing manufacturer. The results were plotted, and percentage reductions in bearing friction displayed on the vertical scale in Figure 5. There are also temperature advantages associated with different oils and different lube application methods (see Figure 6).

Remember, by consistently staying within acceptable ranges of dimensional, material composition, fabrication-specific and application-related parameters, you can avoid process pump failures. Of course, operations, maintenance and project engineering must cooperate. Still, adherence to sound specifications is not difficult once a proper mindset is cultivated. The difficulty is in cultivating the mindset.

About the Author

Heinz P. Bloch

Heinz Bloch works as a consultant for Process Machinery Consulting. He is the author of more than 400 technical papers and similar publications. He has written 17 books on practical machinery ... Read More

Introduction to filters (Engine Oil Bypass Filtration)

Article extract from Reliable plant newsletter:
http://www.machinerylubrication.com/Read/29026/engine-bypass-filtration

Understanding Engine Oil Bypass Filtration

Is your engine’s oil filter performing to your expectation? Do you even know the performance of your filter? Most people don’t, and if they did, they would be appalled.

Some of the best full-flow engine filters on the market perform at a capture efficiency of 50 percent at a particle size of 10 microns and above. That’s a beta ratio of 2 for those of you keeping score, and these are considered “good” in terms of full-flow engine filtration. In comparison, a beta ratio of 1,000 would be considered “good” in terms of industrial hydraulic filtration. Why is there such a performance difference? The following factors contribute to the variance:

Physical Size

Often limited by physical size, engine oil filters are relatively small when compared to their industrial counterparts. This small size coincides with less filter media surface area through which to pass the lubricant.

65%	of lubrication professionals use bypass filtration systems at their plant, based on a recent poll at machinerylubrication.com

Pressure Differential

The pressure differential is the change in pressure from the inlet to the outlet side of the filter. If the pressure differential is too high, a valve will open, allowing the oil to bypass the filter. All engine oil filters or heads are equipped with a bypass valve. This valve is needed so the engine does not become starved of oil as the filter clogs with debris.

The Beta Ratio Test

Oil filters can be tested in a variety of ways, but one of the most common methods is the beta ratio test. This test incorporates online particle counters positioned upstream and downstream of the filter, a continuous flow of test contaminant into the main system reservoir and oil flowing through the filter.

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. For example, you may have a beta ratio or a beta sub 5 (meaning particles larger than 5 microns) equal to 10. This means 10 particles upstream of the filter would be divided by 1 downstream of the filter. In other words, for every 10 particles coming in, one gets through.

If you have a higher beta ratio, say a beta ratio of 100 or a beta sub 5 equal to 100, for every 100 particles coming into the filter larger than 5 microns, one makes its way through.

Every filter will have multiple beta ratios. There could be a beta ratio for 2 microns, 5 microns, 10 microns, 50 microns, 100 microns, etc.

You can also use the beta ratio to calculate capture efficiency, which is the average performance over the filter’s life, with the following formula:
((Beta – 1)/Beta) x 100 As an example, a beta ratio of 10 would yield a capture efficiency of 90 percent:
((10 – 1) / 10) x 100 = 90 percent Therefore, 90 percent of the particles larger than 5 microns are removed by a filter that has a beta ratio of 10.

Flow Rate

In most engine designs, oil must flow through the filter before entering the engine components. Therefore, the filter must be able to handle 100 percent of the flow rate needed to feed the moving components of the engine.

Media Pore Size

The media pore size is the major determinant in how efficient and how small of a particle the filter can remove.

When these factors are combined, a problem arises. The physical size is usually constrained by design. The filter can’t be too large because of all the other components that we are trying to fit under the hood. The flow rate must be high enough to feed all the lubricated components. This means you can’t make the pore size too small or it will raise the pressure differential and the bypass valve will open, effectively rendering the filter useless.

There are a few things you can do to remedy this problem. Enter bypass filtration. Bypass filtration systems take 5 to 10 percent of the flow that would have gone to feed the engine and cycle it through an ultra-efficient filter and back to the sump.

With bypass filtration, the flow rate can be greatly reduced, allowing for a much smaller pore size while retaining a normal pressure differential. The result is much cleaner oil being returned to the sump. Smaller soot suspension and polar insolubles that are not controlled by the full-flow filter can now be taken out of the system. When combined with a full-flow filter, bypass filtration offers the benefits of lower wear generation rates, lower oil consumption, higher combustion efficiency and longer oil life.

In a case study performed by General Motors and published by the Society of Automotive Engineers (SAE), it was determined that engine service life could be extended eight times when 5-micron filtration is implemented vs. the standard 40-micron filtration.

Obviously, having cleaner oil is better for the reliability of the engine. There’s an old saying that oil doesn’t wear out; it just gets dirty. Although there is some validity to the idea that dirtier oil will “age” quicker than clean oil, the engine oil will have a finite life. It will need to be changed eventually no matter how clean you keep it.

While it’s true that a system can remove the majority of suspended soot, wear debris and dirt, the oil and additives are still being decomposed by oxidation and nitration. The depletion of these additives will ultimately be the reason for the oil change. The system should slow down the rate of this depletion, but it cannot eliminate it. Acids, fuel and coolant are just a few of the contaminants that bypass filtration cannot address. They too can shorten the life of the oil.

If you are shopping for one of these systems, it is vital that you do your homework. Not all bypass systems are created equal, and there is a plethora of marketing material out there to make you feel thoroughly confused. Keep in mind that while testimonials may seem impressive, they are not scientific proof. Make sure the manufacturer has SAE and ISO testing to back up its claims.

When installed and maintained properly, a bypass system can provide great benefits. Just be sure to ask all the right questions and have a firm grasp on the concept before settling on a system.

About the Author

Jeremy Wright

Jeremy Wright is a Senior Technical Consultant for Noria Corporation. Hire Jeremy to develop procedures for your lubrication program or to train your team on machinery lubrication best practices. ... Read More

ISO Oil Cleanliness vs Operating Pressure

An informative article I read on Reliable Plant Newsletter this morning.
http://www.machinerylubrication.com/Read/28977/consider-contamination-control

Consider Contamination Control Before Buying Hydraulic Equipment

Brendan Casey  

These days, best-practice contamination control is more like an accepted pre-condition for reliability. Given contemporary advances in technology for excluding and removing contaminants, it could be said that failure to control contamination is a failure of machine design rather than a failure of maintenance.
That said, effective contamination control is not something to be taken for granted. The results you get are only as good as those you demand, which is why it never hurts to be reminded of the reliability benefits of kicking fluid cleanliness up a notch. Consider the following case study:
A sugar mill was operating a fleet of more than 20 sugar cane harvesters. The typical fluid cleanliness of the hydrostatic transmission for the ground drive on these machines was ISO 22/20, and they were suffering regular pump failures - three pumps per machine, per season, on average.
The sugar mill contracted a local hydraulic engineering firm to investigate the recurring pump failures. They recommended a specification change to the ground-drive hydraulic motors and an upgrade of the filtration.
One machine was modified as a prototype, and after showing promising results, two more machines were modified in the first season. The ISO cleanliness code on the three modified machines was 18/15 or better.

71%	of machinerylubrication.com visitors consider contamination control targets before purchasing new equipment

By the fourth year, 15 machines had been modified. The mill was now changing out one variable piston pump per machine every three seasons - a nine-fold increase in pump life.
Armed with this data, the sugar mill convinced the cane-harvester manufacturer to incorporate the same transmission and hydraulic filtration design at the factory.
This is not a scientific study into the benefits of improving fluid cleanliness alone, because clearly, other changes were made to the hydraulic circuit in addition to upgrading the filtration. We’re also not told what influence (if any) these modifications had on other important operating parameters such as pressure and temperature.

Example of Hydraulic Fluid Cleanliness Targets

But what can’t be disputed is the drastic improvement in pump life. As a result, the equipment end user demanded that the machine manufacturer improve the specification (and initial cost) of the equipment they were purchasing. Of course, this was after the economic benefits of doing so had been clearly demonstrated to the end user.
For this hydraulic equipment owner, it was a case of “I once was blind, but now I see.” Prior to this education, they likely would have looked at two cane harvesters of similar capacity from competing manufacturers and bought the cheapest one - with little or no regard to machine reliability or life-of-machine operating costs.

Factors in Setting Target Cleanliness Levels

There are two important factors for hydraulic systems that can help you set target cleanliness levels. One is how sensitive the components are to contaminants. This is called contaminant tolerance.
The second factor is pressure. There is a disproportionate relationship between pressure and contaminant sensitivity. Basically, the greater the pressure, the far greater the contaminant sensitivity the components have to contamination.
After you have considered the component type and the pressure, also consider the duty-cycle severity, the machine criticality, the fluid type and safety concerns. All of these factors collectively can be used to set target cleanliness levels in hydraulic systems.

Even though they got it the wrong way around, this machine owner got it in the end. If you’re a hydraulic equipment buyer/owner, the key takeaway of all of this is that the best time to consider these issues is before you purchase a piece of equipment.
By starting with the end in mind, you get the maintenance and reliability outcomes you desire - before the machine even gets delivered. Like in the cane harvester example, you specify the contamination control targets you want to achieve based on your reliability objectives for the piece of equipment and instruct the manufacturer to deliver the machine appropriately equipped to achieve these targets.
Based on the weight and viscosity index of the hydraulic oil you plan to use, you determine the minimum viscosity and therefore the maximum temperature at which you want the machine to run. You then instruct the manufacturer to deliver the machine equipped with the necessary cooling capacity based on the typical ambient temperatures at your location, rather than accepting hydraulic system operating temperatures dictated by the machine’s one-size-fits-all designed cooling capacity - as is the norm.
For example, say you are about to purchase a 25-ton hydraulic excavator that is fitted with brand “X” hydraulic pumps and motors. According to the pump manufacturer, optimum performance and service life will be achieved by maintaining oil viscosity in the range of 25 to 36 centistokes. You also know that in your particular location that you expect to use an ISO VG 68 weight hydraulic oil, and the brand of oil you are already buying has a viscosity index of 100.
This being the case, the pump manufacturer tells you, based on the viscosity and viscosity index of the oil you plan to use, that if your new excavator runs hotter than 70 degrees C, the performance and service life of the pumps and motors will be less than optimum. Not only that, with 70 degrees C as the maximum operating temperature, the oil, seals, hoses and almost every lubricated component in the hydraulic system will last longer.
So being the sophisticated hydraulic equipment user that you are, you say to the manufacturer before you order the machine: “I expect ambient temperatures at my location as high as 45 degrees C, and under normal conditions (i.e., no abnormal heat load in the system), I require this machine to run no hotter than 70 degrees C. If you deliver it to the site and it runs hotter than 70 degrees on a 45-degree day, then I’ll expect you to correct the problem - at your cost.”
You could continue by specifying other requirements that have an impact on hydraulic component reliability, such as that all hydraulic pumps have a flooded inlet, that no depth filters or screens be installed on pump intake lines and that no depth filters be installed on piston pump and motor case drain lines.
At the very least, as the cane harvester story demonstrates, the next time you or the company you work for are purchasing hydraulic equipment, be sure to define your fluid cleanliness and operating temperature/viscosity targets in advance and make them an integral part of your equipment selection process.

About the Author
Brendan Casey

Brendan Casey has more than 20 years experience in the maintenance, repair and overhaul of mobile and industrial hydraulic equipment. For more information on reducing the operating cost and ... Read More