This article presents, in layman’s terms, information regarding a high-speed electrostatic kidney-loop system, designed to remove submicron particles and other foreign matter (varnish) from lubricating fluids. It is a culmination of more than 30 years of research and development, on-site beta testing, and trial and error, and it has resulted in seven electrostatic filter patents.
The problem in promoting electrostatic filtration stems from the lack of understanding of electrostatic principles. It is a complicated subject that encompasses a combination of physics, chemistry and math.
Electrostatics is the branch of physics that deals with a phenomenon arising from the existence of electric charges. These charges do not move, for they are static. There are a number of laws associated with electrostatics. One of the most important is Coulomb’s Law. The principle of Coulomb’s Law is a fundamental law of nature, which describes the force between charged objects.
Charge is a basic property of matter. Every constituent of matter has an electric charge with a value that can be positive, negative or zero. For example, electrons are negatively charged and atomic nuclei are positively charged. Most bulk matter has an equal amount of positive and negative charge, and thus, has a zero net charge.
Figure 1. Electrostatic Field
Electrostatic Oil Cleaner
The key to maintaining an efficient and effective electrostatic oil filtration system is the product of several coordinated essentials. These include electric field strength, the number of electrostatic fields, flow rate, electrode surface area, and chargeable contamination collection media. The challenge is to manage all the essentials for optimal performance and results, and make them work in unison. Let’s explain how these essential keys work.
Figure 2. Reduction in Varnish and Oxidation Levels
If the flow rate is too fast, you could lose efficiency, and vice versa; if the flow rate is too slow, you might not remove oxidation and foreign contamination material as fast as the lubrication system creates it. It’s a simple formula: if the electrostatic oil cleaner removes insoluble foreign material faster than the lubrication system makes it, then it is a clean system. If not, then the lube oil will oxidize as if there was no electrostatic oil cleaner there, and this creates problems.
Electric Field Strength
To remove contamination particles and oxidation by-product molecules from oil, you must have a strong electric field. This electric field charges the contamination particles, pulls them out of the oil, delivers them to the collection media and bonds them to the sharp edges of that media. Once again, if the electric field is too low, the electrostatic oil cleaner will not remove the contamination particles before the oil has left the electrostatic field.
This means the particle was not removed, and the system pumped the contamination back into the lube oil reservoir. This is an example of poor efficiency, or a phenomenon known as pushing particles. If charged particles are not removed by a collection media in the electrostatic field, then by the laws of electrostatics, that particle now carries a charge inside the oil. It will, therefore, attract and agglomerate with other oppositely charged particles.
Figure 3. Before ISO Code 20/19/17 Figure 4. After ISO Code 9/5/1
In the laws of physics, this means that the contamination particles in the system will grow throughout the lubrication system equally. These particles will eventually get large enough to lodge in the tight tolerances of the system components. It is important to note that the electric field strength must be high enough to draw the contamination particles from viscous oil while in the electrostatic field. All foreign contamination removal in true electrostatic oil cleaners will occur in the electrostatic field, and the contamination will be removed by the collection media.
When two objects in proximity have different electrical charges, an electrostatic field exists between them. An object is negatively charged (-) if it has an excess of electrons relative to its surroundings. An object is positively charged (+) if it is deficient in electrons with respect to its surroundings. This is important because the foreign material and contamination particles which form varnish are small. They are so small that they actually form an insoluble molecule.
The reason electrostatic oil cleaners can remove oxidation by-products and submicron contamination is that even a molecule can take an electric charge in the electrostatic field and then bond to the collection media. Inside a true electrostatic oil cleaner, everything happens inside the electrostatic field. This means that every insoluble foreign contamination particle is removed inside this field, and there is no particle being charged and released back to the oil.
Number of Electrostatic Fields
Society believes that there is strength in numbers, that more is better. For once in the laws of electrostatic principles, this holds true. If there are 16 electrostatic fields versus one electrostatic field, then the higher number will remove more submicron foreign contamination particles.
This one is easy to explain: If a person was a molecule and had to run through one electrostatic field without getting caught in the collection media, he might make it with enough force or velocity. However, even with increased force and velocity, his chances to make it through 16 electrostatic fields without getting caught are cut to 1/16th.
Electrode Surface Area
Electrode surface area is critical in electrostatic oil cleaners because this can make the electrostatic field larger. It’s simple: If you have large high-voltage and negative plates, you will have a large electrostatic field. If you have only two points, much like a spark plug, then you have a small electrostatic field. So in this case, size does matter; the larger the electrode surface area, the larger the electrostatic field is.
We’ve discussed the chargeable contamination collection media and how it relates to the electrostatic field. If the electrostatic oil cleaner had no collection media, it would simply charge particles and then put them back into the reservoir. There would be no noticeable removal of fluid contamination.
Now that we’re familiar with the laws of physics regarding electrostatic principles, you can see why the collection media is important. A durable collection media is necessary to withstand the chemistry of lubrication oil and the contamination particles which have countless numbers of sharp edges. These sharp edges are the target of the charged molecules once they become excited inside the electrostatic field.
Increasing the number of sharp edges can increase the amount of collected material, thus making the electrostatic oil cleaner more efficient. Unlike mechanical filters, where a brand new filter has the highest efficiency when it comes out of the box, electrostatic oil cleaners become more efficient as they collect material. The material forces the collection media to take on a charge and attract more contamination. The contamination in the oil will aggressively keep attracting and bonding to the media until there is enough collected material to increase the electrical current high enough to trigger an alarm.
Once the system alarms, replace the removable collection cartridge. The process then starts all over again. This is important because in this situation, the electrostatic oil cleaner becomes more efficient the longer it runs, as long as the voltage and the electric field strength remain the same. If the collected material increases and the voltage drops, then the electrostatic oil cleaner is losing efficiency.
Kidney-loop Fluid Purification System
Electrostatic filtration is not a new technology. For years, it has been used to remove airborne contaminants. A limited number of oil electrostatic filter designs have been developed, but some fulfill only limited requirements. Removing submicron particles and other foreign matter from oil is difficult. Years of electrostatic R&D, on-site field testing, and experimentation with different oils provided the authors with useful information.
Case Study No. 1
We gathered real-time data from an OILKLEEN electrostatic unit that was being tested at a paper mill for 10 months. In one 15-day period, this unit (operating 24/7) collected more than seven pounds of contamination and foreign matter from a 1,000-gallon hydraulic system. A majority of the material was oxidation by-products (varnish). The seven pounds of contamination was contained in a single foreign matter-collection cartridge. ISO codes during the testing period continually remained below 10/04/00. At the end of the 10 months, it was discovered that this method of electrostatic charging had actually stripped the oxidation and varnish from the interior surfaces of the system.
Case Study No. 2
Information from a GE Frame 7EA field study was collected to show how varnish and oxidation levels were removed in less than seven days. The electrostatic oil cleaner was put on the reservoir in a kidney-loop configuration. An independent lab performed a varnish potential rating test for the gas turbine customer, and determined it was an 85 VPR and had a high ISO particle count of 20/19/17. After seven days with the electrostatic oil cleaner, this VPR rating dropped to 3 VPR and the ISO particle count was 9/5/1. A microscopic photo analysis shows the particle count reduction (Figures 3 and 4).
Introducing new technology is difficult because most of us are resistant to change. These electrostatic filter claims of efficiency had to be proven beyond a reasonable doubt, and the scientists and engineers questioned their own lab reports. We understand their concerns. If for years your lab reports never showed anything below an ISO code 14/12/09 and then suddenly revealed a 09/04/00, that would certainly be cause for concern.