Offline filtration criteria for critical machines

Offline filtration, regeneration, and fluid cleaning systems are becoming an increasingly common sight across industries as more manufacturers and plants recognize the benefits of becoming proactive about oil and fluid cleanliness.

In industries where critical assets like large hydraulic pumps or turbines depend on clean oil, larger, stationary kidney-loop filtration systems are commonly used to extend the service life of lubricants. And while they are small, hand-truck filter carts are often just as important for offline filtration of smaller sumps or gearboxes, along with a variety of other uses. But whether your filtration system fills a room or fits in a box, it should ultimately help you achieve your cleanliness targets, improve reliability, and lower total ownership costs of your assets. The key is choosing the right system (or mix of systems) for your equipment.

Deal with major contamination first

Often, the search for a filtration or fluid cleanliness system begins after uncovering a major or chronic contamination problem. Perhaps a recent repair left contaminants behind that were not properly flushed between drain and fill procedures; or it could be that an incompatible lubricant was inadvertently added to the reservoir, causing chronic oxidation problems. Even “new” oil purchases from your lubricant supplier may be arriving with higher levels of contamination than you realize.

Regardless of the source, your approach to solving a contamination problem should be holistic. Offline filtration is certainly a powerful tool in achieving all the benefits of clean fluid, but in most cases it should be used as the “polishing” step in the process, not as a front-line solution to heavy contamination. Solving gross contamination problems like these is often relatively inexpensive, but it is important to exclude as many major contaminant sources as possible so your offline filtration systems can achieve the kind of cleanliness levels that drive cost reductions and reliability improvements.

Choose the right mix of systems

When it comes to offline systems used to clean fluids, the options can vary widely. Some use conventional filters and pumps, while others may use magnetic, chemical, or other means of separating particles or other contaminants. Both stationary or mobile systems can operate around the clock to remove specific contaminants, continuously cleaning a small percentage of the oil system’s total fluid.

The most common portable option is the filter cart mounted to a hand truck. These carts often utilize an electric or air motor, hydraulic pump, and filters with many available add-ons in a range of sizes and configurations.

Filter Cart Uses

• Transferring lubricants to storage containers
• Transferring filtered oil to a machine
• Cleaning stored lubricants
• Achieving new oil cleanliness standards
• Reconditioning or decontaminating lubricants currently in use
• Draining used oil from equipment
• Providing contamination control functions like hose cleaning, power flushing, directional wand flushing and line flushing

Oil filter carts are often overlooked when it comes to cleaning new oil, but they offer many benefits for handling and storing oil while keeping it clean.

Filter cart dangers to avoid

While filter carts are a common and very useful offline filtration option, if used improperly, they can cause more problems than they solve. Employing filter carts designed for low-viscosity fluids on high-viscosity oils can damage your filter cart, for instance.

But the danger is not just to the cart itself. Utilizing the same filter cart for different lubricants without first performing a thorough oil flush can result in cross-contamination. This can greatly accelerate oil oxidation and degradation, leading to a “sudden death” of your lubricant or unplanned downtime for your machines. Another filter cart problem is insufficient contamination control practices. Where and how you store your filter carts, attachment hoses and connections is important for keeping contaminants out of oils and hydraulic fluids. An unsealed, dirty or wet environment will contaminate filter carts, leading to higher contamination in your equipment.

Look at more than up-front cost and price

Because the market has such a wide range of options and prices, choosing the right oil filter can be a challenge. Purchasing filters based only on price tends to mean sacrificing filter performance and longevity in the name of short-term savings. But because cheaper filters are less efficient and need to be replaced more frequently, they tend to increase total ownership costs rather than decrease them. High-quality filters, although more expensive per unit, last longer and are more efficient, saving not only the cost of purchasing and shipping replacement filter elements, but the labor needed to complete frequent replacements.

When selecting a conventional filter, you should consider these specifications and how they match up to OEM recommendations:

• Flow rate: the amount of oil that can pass through a filter in a given period of time.
• Filter media: the material inside a filter used to capture contaminants.
• Dirt-holding capacity: the amount of contamination that a filter can hold before it becomes ineffective. This capacity is important for gaining a thorough understanding of how often filters will need replacing and the associated cost of replacement filter elements and installation.
• Capture efficiency: a filter’s ability to capture and retain particles of a specific size; often expressed as a filter’s beta ratio. If your filter supplier does not offer a beta ratio specification, ask for one.

Most filter manufacturers will run their products through a series of tests designed to capture particles of specific sizes. They measure the number of particles downstream of the filter and compare that to the total number of particles that were originally introduced during the test. The result of the testing is displayed as the beta ratio at a given micron size. A filter with a beta ratio of 75 or greater is considered an absolute filter (it is capturing particles of the given size at a rate of 98.7%), where a filter capturing at 90% or less would be considered a nominal filter (a beta ratio of 10 or less).

When selecting a filter, it is essential to consider the application and the fluid with which the filter will be used. For systems like turbines and hydraulics, which require a cleaner lubricant, a higher-quality filter will usually be needed. For example, a hydraulic system’s specifications might call for a 4-micron filter      

Narrow options using system constraints

Optimizing your offline filtration choices must take into account your oil or fluid system’s constraints and your goals for cleanliness, service life, and reliability. There are a handful of questions to ask about the targeted systems before selecting elements and hardware, including the following:

1. How clean is the fluid under current conditions?
2. What is the new target cleanliness level?
3. If the system is portable, how long can it run once it is put into operation? If stationary, will it circulate oil quickly enough to keep up with incoming contaminants?
4. What will the fluid viscosity be during filtration?
5. What is the sump volume?

The selection of filter elements and hardware can be a sliding scale based on the answers that exist to these questions. A couple of key principles to consider are:

1. If the flow is constant, as the operating viscosity increases, the element size should also increase.
2. As the flow increases, element effectiveness may decrease.

What does this mean in practical terms? Higher flow does not necessarily lead to improved filtration effectiveness.

Cost of Ownership

As mentioned above, looking at contamination control holistically leads to better results in offline filtration system selection. Making choices based on the initial cost of the system alone could mean unexpectedly high total ownership costs due to increased maintenance activity and required consumables over time. It is common to find that a system which seems cheaper initially proves to be up to five times more expensive to operate over a few years. By accounting for total cost of ownership in advance, we get a much clearer picture of the return on investment associated with quality filtration and fluid cleaning choices.

Remember, there is no one-size-fits-all solution when it comes to offline filtration or oil regeneration systems, but if you understand your cleanliness targets, needs, and goals, asking these questions can help you find an answer that lowers total ownership costs.