Signs it is Time to Replace Filter Elements

Most industrial filter elements are disposable and must be replaced periodically.  It is important to monitor the performance of filters and understand the signs that it is time to replace the elements. Before examining this in more detail, consider the general construction and operating characteristics of cartridge-style filter elements.

For our purposes we will consider a cylindrical (candle type) filter cartridge.  Used in swimming pools to industrial hydraulics this is very common style.  These filter cartridges consist of a cylindrical structure that supports any number of materials that serve as the filter media.  As fluid flows through the cartridge, it passes through the media where solid contaminants are trapped.  As the contaminants accumulate and block the flow channels (or pores) in the media, flow is restricted and differential pressure across the media increases.  This pressure drop is the most important parameter to monitor.  

Gauges, transmitters, service indicators or other sensors are commonly used to monitor the status of filters.  Initially and for most of a filter’s life, pressure differential across it increases gradually in linear fashion.  However, near the end of its service life, the pressure drop accelerates sharply.  This indicates that it is time to prepare to replace the filter elements.  In a relatively short period of time the pressure drop will reach the manufacturer’s recommended maximum and the cartridge should be changed.  This is the normal course of a filter element service life.

As with everything, there are a few exceptions.   Let’s consider the signs that something has gone wrong even though the pressure drop may seem okay. Knowing these can prevent serious process problems that result when spent filter elements go unnoticed.

Signs of a problem:

Equipment failure – If a machine has failed due particulate contamination, this is the most obvious and urgent sign that a filter element needs to be replaced.  Unfortunately, purpose of the filter was defeated and the equipment it was supposed to protect failed.  This is almost certainly much more costly than replacement elements.  This shed light on the value of proper monitoring and training focused on critical filters.

Signs of equipment fouling – When a filter is in service too long there is significant risk that contaminant will start bypassing.  There are several possible causes for this, including damage to the filter cartridge, opening of filter bypass valves and filter unloading.  The latter refers to the dislodging and migration of contaminant through the filter due to excessive pressure and/or high fluid velocity within the media. If contaminant bypasses the filter there is a significant risk that it will accumulate in/on downstream equipment.  This fouling manifests in many ways. Smoky exhaust, vibration, sputtering, plugged guard filters, low oil pressure and sluggish controls/response are just a few of the possible symptoms.  However, this is greatly dependent upon the type of equipment.  The signs of equipment fouling should be researched, posted and used for training purposes.

Reduced flow of the filtered fluid – Without any pressure compensation, the flow of filtered fluid will decrease in proportion to amount of contaminant trapped in the filter.  This is a result of increasing pressure loss as trapped contaminant accumulates and blocks flow channels (pores) in the media.  Depending on the fluid system and the equipment design low flow may cause several problems.  Again, this should be researched, posted and used for training.  When signs of low fluid flow appear, one of top items on the troubleshooting list should be to check all upstream filters.  

Spike in transmitter data – Dialing in the time resolution and reviewing the minute by minute data logged by a filter’s pressure transmitters is an often overlooked and very useful diagnostic tool for filters.  Unlike lower resolution trending, zooming in and reviewing the log or even trending at higher resolution can uncover a spike that resulted in filter damage that, in turn, resulted in a drop to zero or a nominal differential pressure.  Fluid contamination often occurs in bouts related to process or environmental upsets.  When a bout occurs, it may overwhelm the filter causing the differential pressure to spike.  The sudden high pressure could rupture or collapse the filter element immediately.  This usually relieves the pressure and the gauges or transmitter readings drop to a unalarming level.  This could mislead operators and result in a perplexing equipment malfunction that could remain unresolved until further equipment damage, complete failure or a safety issue occurs.  When a filter seems to be lasting much longer than expected or there is equipment malfunction that could be related to a poorly performing filter, it is always wise to either visually inspect the filter elements or review the transmitter logs for a seconds to minutes-long spike in differential pressure.

Filter material found in equipment or reservoirs – Usually if this happens it means the filter either ruptured, collapsed or underwent another form of mechanical failure due to a pressure spike or a temperature or chemical incompatibility.  Unfortunately, if the filter is coming apart and making its way into downstream equipment, serious problems have likely already occurred.  Obviously, there needs to be an investigation into the cause of the failure and the filter elements need to be replaced with a suitable alternative.

One final piece of guidance with regards to monitoring and care of filter elements concerns process exposure time.  There are many possible mechanisms that are responsible for exposure-related filter media degradation, including thermal, chemical and pressure cycling and more. It is a good practice to get an estimation of the shelf life and application specific exposure limits for each type of filter.  This will not be the same for all filters in all applications.  Obviously, the process has a significant effect on the rate of degradation of various materials.  Exposure degradation, such as fiber oxidation, can result in poor performance and mechanical failure prior to a filter reaching its maximum rated differential pressure (contaminant capacity).  Applications with very light contaminant loads may require periodic filter replacement based on exposure time.

Similarly, filters behave differently when they are exposed to multiple fluid phases.  If a filter is operating in liquid phase and gas bubbles are present, this could result in higher differential pressure. It may be necessary to periodically bleed the gas from the filter housing to reduce pressure.  Likewise, if a filter is operating is dry gas phase and entrained liquid wets the filter media, this will result in more pressure drop and may wash contaminants out of the filter.  

Filters are a very important and often misunderstood component of many processes and equipment systems.  It is advisable to investigate and understand the application of each filter and ensure that operations and maintenance personnel are properly trained.  Simply monitoring filters and replacing the filter elements as required could avert serious operational issues and improve a systems overall performance.

The points above, are intended to help understand critical filter performance and operating characteristics and how these are related to filter element service life.  The objective is to provide guidance on how to monitor and identify when it’s time to replace filter elements.  When the time comes, searching the vast landscape of the internet will lead to myriad options for filter elements and suppliers.  Considering the importance of understanding filter characteristics and their applications, the advantages of working with a filtration specialist instead of a retail outlet should be obvious.  PowerFlow Fluid Systems offers hands-on experience with all types of filtration equipment and applications.  Contact us today for filtration products, services and free consultations.

PowerFlow Fluid Systems supports industrial sustainability with innovative and environmentally responsible solutions for optimizing performance of virtually all fluid systems throughout the plant.  https://www.pwrfs.com/

Understanding and Evaluating Lube and Hydraulic Oil Purification Systems

Lubrication and hydraulic fluids for industrial machinery will most often suffer from water contamination. AMPTIAC Quarterly reports that, 75% of hydraulic system failures result from fluid contamination. Water is second only to particulate as a source of major contamination of machine oils. Rotating equipment is especially vulnerable. For example, as the water content in turbine lube oil gradually increases, the machine begins to develop multiple failure points. These include bearings, bushings, seals, shafts and more.

While other forms of contamination must be mitigated, water contamination presents unique challenges. Free and emulsified water are easily identifiable. Free water accumulates and stratifies, while emulsions typically appear as cloudiness or rag layers. Dissolved water is invisible but just as toxic as the other forms. According to NORIA, “Depending on the oil type and temperature, a bearing can lose 75% of its life due to water contamination before the oil becomes cloudy.” Reducing water content well below the saturation level is obviously desirable. This prevents the liberation of free water in oil coolers, while curtailing additive depletion and degradation of critical oil properties such as viscosity, lubricity, and film strength.  “Oil Purification Systems,” aka “Oil Purifiers” utilizing vacuum dehydration were designed for these challenges.

As defined here, their primary function is to remove ALL forms of water from the oil. Most, also remove free and dissolved gases, as well as particulate contamination. Hence, as used here, the term “Purifier” or “Purification System,” alludes to the removal of free and dissolved water and gases, oil/water emulsions, and particulate. Though often advertised to the contrary, most oil/water separation technologies do not purposefully remove dissolved water nor any gases. This is where systems that utilize vacuum dehydration are distinguished from those employing coalescing filters, water absorption media, corrugated plates and centrifuges. Application of an Oil Purification System utilizing vacuum dehydration is necessary when total water content starts to increase in lube or hydraulic fluid systems.

Sources of Water Contamination

There are several ways water enters lube and hydraulic fluid systems. These include:

1. Direct absorption from humid air in the headspace of the oil reservoir.
2. Rapid condensation in the headspace of the oil reservoir.
3. Rain and/or washdown water ingression through leaky hatches and seals.
4. Leakage from steam seals.
5. Leakage from oil coolers and heat exchangers.

Preventative measures for mitigating these ingression mechanisms should be in place.  However, it is very probably that water will find its way into these systems at some point.  This is when an Oil Purifier is convenient and often the most reasonable solution.

Process Technology Applied in Oil Purifiers

Before exploring the benefits of using Oil Purifiers, it is essential to understand how they work. Commonly, Oil Purifiers utilize vacuum dehydration technology for enhanced water removal performance. In some systems the oil may also be heated to optimize the dehydration process. Under vacuum, the required thermal input is reduced for the purpose of preventing thermal oxidative stress of the processed oil. Vacuum dehydration is the most efficient way to reduce water concentration levels below the threshold required to adequately protect vital machine components.

There are two commonly used vacuum dehydration processes, “vacuum mass transfer” and “flash distillation”. Vacuum mass transfer uses moderate vacuum levels (ࣘ≤22inHg) and heat (≤120 deg. F) in a process that accelerates moisture evaporation with minimal risks of oil degradation. Flash distillation uses deep vacuum (25-28 inHg) and high heat (150+ deg. F) to boil or flash water from the oil in a process carrying a higher risk of oil degradation. We only discuss vacuum mass transfer here.

Inside these dehydrators, the oil is distributed in a thin film over some form of media, such as packing rings. The increased surface area greatly improves the efficiency of the process. To achieve this,

• There is a vacuum chamber/tower in which oil flows from top to bottom, while dry air flows from bottom to top.
• There is a means of distributing the oil evenly over the inside cross section of the chamber/tower by creating an oil spray in the form of an umbrella.
• The oil passes from top to bottom through/over a media such as packing rings that expands the surface area and creates a thin, cascading film.

Dry air is continuously drawn across the oil surface, evaporating water and sweeping it out of the vacuum chamber along with any free and dissolved gases. Dehydrated oil exits the chamber and is typically routed through a particulate filter to achieve the desired level of cleanliness. This system could run as a batch or continuous process, but the latter tends to be more efficient.

Why Use Oil Purifiers

Before investing in an Oil Purification System, it is essential to consider the long term benefits.

Benefit #1: Improved safety

Safety is always number one. Particularly with respect to rotating equipment, mechanical failure and control issues can result in serious accidents. The average cost of a recordable injury is tens of thousands of dollars. A lost-time injury costs even more. By maintaining the purity of lube and hydraulic fluids, dangerous equipment failures such as broken shafts and hydraulic overspeed’s can be avoided. Prevention of a single injury will always justify the cost of an Oil Purifier.

Benefit #2: Less frequent oil changes

It is easy to see how stretching the useful life of lube and hydraulic fluids is economically beneficial. Factors like:

• Reducing the money spent on replacement fluid
• Lowering labor costs and freeing up time for other maintenance and repair projects
• Shrinking disposal fees

Have a significant impact on the return on this investment. Accordingly, extending the lifespan of the oil by several thousand hours makes a good case for investing in an Oil Purification System.

Benefit #3: Less unscheduled machine downtime

Often, machinery endures major wear and tear or massive and sudden breakdowns that can cause immense losses to a business. According to Forbes magazine “next to a safety or environmental mishap, unplanned/unscheduled downtime represents one of the costliest events at any industrial or manufacturing plant.”  Every event is different, but costs can run into millions of dollars. It is almost certain, when the downtime results from contaminated lube or hydraulic fluid, the costs will dwarf that of investing in an Oil Purifier. Machinery Lubrication published the following top reasons that unscheduled downtime is unwelcome:

• Production losses and schedule delays (business interruption)
• Lost revenue and profit (unhappy management/ownership)
• Promised delivery dates are missed (unhappy customers)
• The blame game and damaged relationships between operations and maintenance (morale issues)
• Hurried (botched) repairs cause future problems (cycle of despair)
• Lack of available replacement parts and skilled trades prolongs the downtime interval
• Repairs are at a “cost premium” due to rushed parts purchases, use of overtime labor and collateral damage
• Scheduled “proactive” tasks are replaced by chaotic reactive tasks (leads to future problems)
• Increased work pressure and job stress (job satisfaction issues)
• Safety risks due to rushed work, unskilled work, inferior parts, cutting corners, job stress, etc.

Alone, any of these demonstrates the value and ROI of an Oil Purifier.

Benefit #4: Better machine performance

The productivity of a company depends on how well equipment runs. When lube and hydraulic fluids are properly maintained, it elevates machine health. This results in better performance, higher availability and productivity. It also promotes a safer work environment and smaller environmental footprint.  On the other hand, contaminated lube and hydraulic fluids leads to derated capacity, sluggish operation, hydraulic control issues and other performance issues. Plant Services’ surveys indicate, one of the most important metrics used by the energy industry is “return on capital employed,” which correlates with the performance of rotating equipment. This suggests that if rotating equipment is underperforming due to contaminated lube or hydraulic fluid, investment in an Oil Purifier may have a significant and favorable impact on key business metrics.

These and other benefits unique to every plant offer extensive, quantifiable justification for capital investment in an Oil Purification System. If capital is tight, rental units are available that will protect machines through a budget cycle. There are many sizes and features for consideration, making it possible to find a system that suits any needs or budget.

How to Evaluate Oil Purifiers

With many Oil Purifiers available in the market, it is important to understand the method of purification and how to evaluate them. The characteristics that are most important will determine whether this investment meets your expectations. Doing some homework and making an educated decision is vital.  The most important machine attributes relate to operational complexity, reliability, and oil processing performance. The best Oil Purification Systems will:

• Effectively remove all forms of water, gases, and particulate from oil with no oil degradation or additive depletion.
• Require minimal operator attendance to start, stop and run the unit.
• Offer adequate, simple and convenient monitoring and control.
• Require minimal scheduled or routine maintenance.
• Operate at full capacity over the entire range of application conditions, including oil temperatures, pressures and viscosities, piping configurations, and environmental conditions (including sound levels).
• Produce minimal environmental footprint.
• Operate with minimal energy and utility requirements.

The best way to evaluate these important qualities is to compare systems with a full-scale, onsite trial. Nothing beats a test drive. In this scenario, ensure that a knowledgeable factory or distributor representative is onsite during the trial to answer questions, train and assist the personnel conducting the test. It would also be beneficial to have the operations and maintenance staff participate and provide input in the evaluation. 

The next best alternative is to request a copy of the O&M manual. A thorough review of this document with the previously mentioned attributes in mind can provide useful information. For example, it will likely contain:

• A list of operational limits
• Important installation requirements
• Detailed start-up, running and shutdown procedures
• Component maintenance requirements
• Critical safety environmental and hazard information

Often, sales and marketing material omit much of this, but it can be found in technical documentation provided upon delivery of the machine. Do not be afraid to request additional documentation, data and drawings. Sales personnel should be able to help with this and provide valuable contextual information.

Conclusion

As you can see, an Oil Purification System can be very beneficial to any business that relies on lubricated or hydraulically operated machinery. Fluid health is critical to machine health. Industrial data suggests that the health and reliability of the machinery used by a business correlate to productivity, profit, safety and environmental metrics. Consider the impact that could be realized by making a wise investment in an Oil Purification System.

Start your research now and consider companies like PowerFlow Fluid systems, who offers decades of experience designing and building the best Oil Purification Systems.

PowerFlow Fluid Systems supports industrial sustainability with innovative and environmentally responsible solutions for optimizing performance of virtually all fluid systems throughout the plant.