Effect of filtration on oil additives – where does efficiency end and losses begin?

excessive filtration

Excessive filtration can lead to the removal of valuable additives that are responsible for corrosion protection, lubricating properties or thermal stability, among other things. In this article, we explain how to find the golden mean between oil cleanliness and functionality – and why a customized approach for each machine is key.
 

from the article you will learn:

• Why oil filtration is not only a matter of cleanliness, but also of preserving its properties.
• How excessive filtration can negatively affect additives in oils.
• What to follow when determining oil cleanliness levels for specific machines.
• What is the importance of design tolerances and equipment operating conditions for effective filtration.
• In which cases, filters that are too precise can do more harm than good.
• Why you should consult the selection of filters with the manufacturer of the device or a specialist.

what does oil consist of and how do additives work?

Lubricants are essential for the efficient operation of all machines, reducing friction, wear and protecting against corrosion while ensuring smooth operation. Industrial oils consist of a base oil and a package of additives. The base oil determines the properties of the lubricant because it is responsible for, among other things, its viscosity and creates an “oil film” layer separating the moving surfaces from each other, while the presence of additives gives the base oil new properties, including delaying the loss of certain properties or improving other existing properties. Enable also the oil to achieve its characteristic final required parameters.

Additives are organic or inorganic substances dissolved or suspended (as solid particles) in oil. These additives include oxidation inhibitors, corrosion inhibitors, viscosity index improvers, foam inhibitors, anti-wear additives, detergents and many others. Each of them performs a basic function, usually indicated by its name. However, their functions are not unlimited while using a given oil in the device. Over time, additives are exposed to conditions that cause their ability to decrease or become depleted.

Take for example oxidation inhibitors also known as antioxidants, they aim to delay the oxidation process and its negative effects, including the formation of acidic products and deposits. As with oil oxidation, most additives can become depleted over time due to exposure to the various operating conditions encountered in a given machine.

additive depletion mechanisms

We distinguish three basic mechanisms of additive depletion: decomposition, physical removal and adsorption.

Decomposition – It is a mechanism of breakdown of additives by changing their structure, resulting in the formation of harmful acidic products in the oil. Causes for this are processes such as oxidation, hydrolysis, thermal degradation, and shearing of molecular chains of particles.

Adsorption – division

• Surface – involves the deposition of additives on the surface of elements, creating a protective layer.
• Polarity – additives may be attracted to solid particles due to their polarity, causing them to be retained in the filter or to sink to the bottom of the tank.
• Water washing – as water is polar, additives can be attracted to water particles and fall to the bottom of the tank.

In the category of physical removal we can distinguish methods such as: condensate settling, centrifugation, evaporation, filtration.

• Condensate Settling – If additives become insoluble due to combination with contaminants, high temperature or other operating conditions, they will have a greater tendency to settle under gravity to the bottom of the tank.
• Centrifugation – High centrifugal forces can cause additives to separate from the lubricant. Centrifugal filtration, used in some applications to remove contaminants, can have this additional undesirable effect.
• Evaporation – a rare phenomenon, however, some additives may evaporate, especially when vacuum dehydrators are used to remove water from the lubricant.

filtration and its impact on oil condition

When it comes to oil filtration, you may wonder if more is always better. The answer is not as simple as it may seem. Cleaner oil has been proven to reduce wear on bearings and machinery, extending the life of your equipment. However, when trying to meet ISO cleanliness standards, there are a few things to consider.

The first thing to consider is the machine tolerances and the need for suitably clean oil. Different types of machines have different requirements. For example, hydraulic systems typically require much higher standards of oil cleanliness compared to industrial gears. This does not mean that transmissions do not need clean oil, but rather that they tolerate “dirty” oil better than hydraulic systems. When determining the level of cleanliness, the construction of the machine, its age and criticality, equipment costs and operating conditions must be taken into account.

Once you have your cleanliness goals set, it’s time to choose filters. There is a wide range of filters available on the market, depending on type, efficiency and price, so choosing the right oil filter can be a challenge. A common criterion when choosing a filter is the price alone, which guides the buyer, regardless of the filter’s efficiency and durability in the name of short-term savings. However, this is a misconception because cheaper filters are usually less efficient and require more frequent replacement intervals. Advantage of more expensive, higher-quality filters is that they last longer and are more efficient, which in the long run can reduce the operating costs of the devices.

Micron sizes are typically considered the benchmark for evaluating filter performance, but this rating only tells part of the story. To get a complete picture of filter performance, the beta coefficient must be taken into account. Typically, filter manufacturers use general terms to characterize a given product, including: dirt holding capacity, flow coefficient and particle capture efficiency of a given size. All these terms may be foreign and confusing to people unfamiliar with this matter.

Most commonly used terms to describe oil filter characteristics:

• Filter material – the material inside the filter used to capture contaminants.
• Micron Size – The size of particles a filter can capture.
• Capture Efficiency (Beta Factor) – The efficiency of a filter to capture particles of a given size.
• Dirt holding capacity – The amount of dirt a filter can hold before it becomes ineffective.
• Flow rate – the amount of oil that can flow through the filter in a given period of time.

 
Most leading filter manufacturers subject their products to a series of tests to capture particles of specific sizes. The number of particles downstream of the filter is measured and compared to the total number of particles that were originally introduced during the test. The test result 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. Such a filter captures particles of a given size with an efficiency of 98.7%, while a filter capturing 90% or less is considered a nominal filter (Beta factor of 10 or less).

When choosing a filter, consider the application and the type of liquid that will flow through filter. For systems such as turbines or hydraulic systems that require a cleaner lubricant, a higher quality filter should be used. For example, hydraulic system specifications may require a 10-micron filter with a beta coefficient of β=200. This means that out of two hundred particles with a size greater than or equal to 10 microns that hit filter, only one particle will pass through it and the remaining 199 will be retained in filter, which gives a filtration efficiency of 99.5%.

In addition to the issues discussed above, there are many more factors relating to the operating conditions and nature of the device, its location, surroundings and environmental factors that may impact specific filter needs. Therefore, before deciding on the selection of a specific filter, it is worth consulting with filter suppliers or the device manufacturer.
As filters become more accurate, they can negatively impact the condition and performance of lubricants, usually by removing additives.

Solid or condensed additives can be physically removed from the lubricant by filtration. Solid additives that can experience this include, for example, silicone anti-foaming or anti-corrosion agenst, for example, used in specialist oils for screw compressors compressing chemically active gases, or molybdenum disulfide (MoS2) improving lubricating properties, which is a component of some CLPF class oils used in some heavily loaded bearings or gears, this makes it possible to achieve higher efficiency over a wide load range.

This type of additives are commonly separated from oil during filtration. In other cases, additives that adsorb contaminants may also be retained by the filter during filtration of the particles to which they are attached. Some types of filter media, such as fuller’s earth, are chemically active and can remove polar additives from the oil. n the case of very effective filters with a pore size of <5 microns, even additives dissolved in the oil can be removed.In summary, when it comes to filtration, there is no one-size-fits-all approach. Every machine has different cleaning needs and each should be considered individually. When it comes to over-filtration, the goal is to maintain balance – more thorough filtering is not always the desired solution to ensure purity, but may have a negative impact on the properties of the oil, depriving it of its intended functions in the lubrication system and thus disqualifying the oil for further use.

worth remembering:

• More is not always better – overly thorough filtration can remove additives essential to oil performance.
• The choice of oil cleanliness level should be individual – it depends, among other things, on the type of machine, its age, criticality and operating conditions.
• Some filters can remove polar additives and physically condensed components – such as anti-foaming, anti-corrosive or lubricating agents.
• The environment and work environment affect filtration needs – so filter selection should not be random.
• Filtration is a compromise – the goal is to protect the system, but with the properties of the lubricant preserved.
• Any doubts? Consult the experts – it’s a good idea to coordinate filter selection with the machine manufacturer or lubricant supplier.