TOP-OEL Oil Micro Filtration Manual

Technical Information of Oil management by TOP-OEL micro filtration Contents: Chapter 1 Lube oil general Chapter 2 Lube oil filtration Chapter 3 Lube oil additives Chapter 4 Influence on the oil condition Chapter 5 Impact on the engine condition Chapter 6 Perkins report Chapter 7 Installation instructions Chapter 8 Flow check Chapter 9 Various filter types CHAPTER 1 - LUBE OIL: GENERAL In this chapter we will successively deal with: 1.1 The functions of lube oil 1.2 Oil change intervals 1.3 Measure points in the specification 1.4 Review of specification boundary values 1.5 Example of an oil analysis report 1.1 THE FUNCTIONS OF LUBE OIL Lube oil consists of a base oil - mineral or synthetic - and a variety of additives - dopes. Its task is: ¾ lubrication - of the moving parts ¾ cleaning - by absorbing impurities ¾ cooling - by absorbing heat ¾ sealing - of the clearance between the piston ring and cylinder lining To successfully accomplish these tasks the oil has to meet a specification. 1.2 OIL CHANGE INTERVALS As long as the oil meets the specification as outlined by the oil and/or engine manufacturer, it is suitable for use The pre-establishment of an oil change interval by the engine manufacturer is no more than a general guideline: it is a safe average of regular use based only on filtration through the full flow filter. What really matters is the actual condition of the oil itself. As long as this is within specification, it is non-sense to waste the oil. Therefore, what it amounts to is to keep the oil within specification on all points. 1.3 MEASURE POINTS IN THE SPECIFICATION The indicated boundary values are general norms as provided by a number of oil companies. * Viscosity: This is the thickness of the oil at a certain temperature. In analysis it is measured at 40°C or at 100°C in mm² 0/sec. For an adequate lubrication the film forming properties of oil are important. The oil must not be too thick or too thin. Normally the oil becomes thicker (the viscosity increases) with use. This is primarily a result of contamination with soot. On the other hand it can happen that the oil, because of spills of fuel which mix, becomes thinner. This is always caused by a mechanical error (leaking atomiser) which should be cured quickly. Boundary value viscosity: not less than 75% and not over 135% of the viscosity of new oil (The viscosity of new oil can be obtained from the relevant oi1 company). * Pentane -insoluble: Measured in % relative to weight. The insoluble to a large extent consist of soot. Too many particles lead to a too high a viscosity. Boundary value pentane inso1ub1es: maximum 4%. * Flash point /- Fuel content: Through spillage of fuel the flash point of the oil decreases. It is evident that oil is not supposed to burn. Boundary value flash point: not below 200°C. Boundary value fuel content; maximum 5%. * Water content: When burning 1 litre of fuel approximately 1 litre of water is generated, which evaporates to a large extent. Water in emulsified or condensed form in oil causes acidification and formation of sludge and is generally an enemy of oil. Boundary value water content: maximum 0.3% relative to weight. * TBN Number: This stands for Total Base Number, or the alkaline reserve of the oil. The TBN is measured in mg KOH per gram. A base is the opposite of an acid. Bases can neutralize acids. That is why bases are added to oil to fight acid formation. The TBN number measures up to what degree this base reserve is still available. Boundary value TBN: not less that 30% of the TBN of new oil (The TBN for new oil can be obtained from the relevant oil company). * Wear metals: These are wear metals from the engine, which have entered into the oil. They are measured in p.p.m. (Parts per million). These additive metals, because of their hardness, cause abrasive wear (scraping and scratching) in the combustion chamber and stimulate oxidation of the oil. The most frequent is iron, and in analysis reports lead, copper, nickel, tin, chrome and aluminium are also often measured. Boundary value metal (iron) particles: maximum 100 - 150 ppm. (ppm. is also mg/kg). * Silicon: Silicon is found in sand and dust particles and is also measured -in p.p.m. Silicon is even harder and therefore even more dangerous for the engine than most metal particles. It enters through the air inlet of the engine. Boundary value silicon; maximum 20 - 30 ppm. The above are the most important measure points to define the right moment for changing the oil. As soon as the limit has been clearly exceeded on one or more of the measure points, even if this were to be the case after only 1,000 km, the oil needs to be changed. The following table summarises the critical boundary values. 1.4 REVIEW OF SPECIFICATION BOUNDARY VALUES Viscosity mm/sec min 75% / max 135% of new oil Insoluble % mass max 4X Flash point °C min 200°C Fuel content % volume max 5% Water content % mass max 0. 3X TBN number mg KOH/gr mm 30% of new oil Iron (FE) ppm (mg/kg) max 100 - 150 ppm Silicon ppm (mg/kg) max 20 - 30 ppm 1.5 EXAMPLE OF AN OIL ANALYSIS REPORT Using the above table one can read and judge any analysis report. As an example we take an analysis report by the surveyors Caleb Brett. This concerns a test of the TOP OEL®-Filter by Deutz Diesel BV on a Deutz engine type F8L413F used in a shunting engine which worked under relatively difficult operating conditions at Nieuwe Matex Botlek (see also the Deutz test report in the presentation folder). CHAPTER 2 - LUBE OIL FILTRATION In this chapter we will successively review: 2.1 Influencing factors of the oil condition 2.2 Filtration 2.3 The TOP-OEL -Filter 2.4 Bypass filtration 2.1 INFLUENCING FACTORS OF THE OIL CONDITION These can be outlined as follows; INFLUENCING FACTORS OF THE OIL CONDITION Of the above motor type, running time, adding and consumption are fixed factors. Variables remaining as negative factors are contamination, chemical and physical ageing and as a positive factor the retention by the filtration system. Note: Ageing is a term used for deterioration. In this sense it has no relationship with the actual time factor. The chemical and physical ageing require further explanation. Chemical Ageing: We distinguish two processes; oxidation and acidification. * oxidation: Is the reaction with oxygen. Oxygen breaks down the original material: iron + oxygen = iron oxide = rust In the case of oil the oxidation takes place under high temperatures in a chain reaction which breaks down the oil molecules with an ever increasing speed. The (intermediate) materials which are formed in this reaction are often acidic and in crease the viscosity. A characteristic of oxidation of oil is that the reaction is accelerated by the presence of small particles of iron or copper. These wear metals in fact act as a catalyst and cause a much more rapid oxidation reaction. The contamination, in this case by metal particles, thus stimulates the oxidation to a large extent. * acidification: Caused by acid oxidation products and sulphuric acid formation: water + sulphuric oxide = sulphuric acid H2 O + SO3 = H2SO4 The formation of sulphuric acid over the past years has been somewhat reduced in Europe since the sulphur content in fuel was reduced. Physical Ageing: With these words we simply describe the increase in viscosity of the oil. This-is primarily caused by the increased soot concentration which causes the oil to become thick. Conclusion: The contamination with wear metals, water and soot is the main cause for both the chemical as well as the physical ageing of oil. The -influencing factors of the oil condition can therefore be simplified as follows: INFLUENCING FACTORS OF THE OIL CONDITION In short: The deterioration of the oil condition is caused by the contamination of the oil. The solution lies in fi1tration. 2.2 FILTRATION The contaminating particles which are important are smaller than 15 micron (1 micron = 1/1000 mm). The vast majority of these particles - about 80% - are between 0.5 and 2 micron. The familiar graph from the brochure shows this clearly. For a filter to be really effective, it must have a retention value of 0.5 micron or smaller. Additionally the filter must be able to absorb water (and acids). It is evident from the graph that full flow filters (the finest known to us have a retention value of 15 micron) are not at all effective. The full flow filter is absolutely essential for the protection of the engine against relatively large particles (a normal grain of sand is approximately 100 micron), but as an oil cleaner -it is useless and has as such no impact at all on the condition of the oil. 2.3 THE TOP OEL - FILTER The TOP OEL®-Filter on the other hand does have a cleaning effect. The TOP OEL®-Filter cartridge comprises a perforated cardboard cylinder, around which a strip of paper of approximately 55 meters -in length has been wrapped in 256 windings. The oil flow through the filter is radial (from outside to inside) and has to pass these 256 windings layer-by-layer. The retention process that takes place m the TOP OEL®-Filter is known as adsorption (insolubles) and absorption (fluids). The resulting retention value is 0.5 micron nominally. This means that particles larger than 0.5 micron are retained, although some particles between 0.5 and 1 micron can pass through the filter. Particles in excess of 1 micron are almost certainly retained. The liquid absorption capacity is 150 ml water (TO-26E). Although this does not look impressive, it is more than sufficient for engines, unless there is a significant leakage of the cooling water. In that case the TOP OEL®-Filter will block. Upon being checked by hand touch it will not feel warm and in this way it warns that something is wrong. In practice cooling water leakages have been noticed several times in this way, preventing major engine damage. 2.4 BYPASS FILTRATION In an average engine the oil is transported to the parts that need lubrication at a speed of somewhere around 100 litres per minute. Under these circumstances a full flow filter can never filter fine particles without slowing down the flow of oil. A fine filter or a micro filter is therefore connected in bypass. A bypass is a small parallel circuit round the engine lubrication areas. Thus, the oil flows from an oil pressure point via the micro filter back into the sump. The following diagram shows the position of the bypass filter in the oil circuit: The nominal speed at which the oil flows through the TOP OEL-Filter (TO 26) at working temperature and pressure is 1 litres per minute. On one hand this is but a small percentage of the total oil flow, leaving the main flow intact. On the other hand it is more than adequate to thoroughly clean the oil (1 litres/minute = 60 litres/hour). As the filter cartridge becomes saturated with dirt the oil flow through the filter will gradually reduce. For changing the cartridge one should not wait until the filter is totally blocked. One should apply the recommended changing intervals, thereby allowing sufficient oil to flow through at all times. A question often heard is "Why does oil flow through the TOP OEL®-Filter at all? Oil always follows the path of the least resistance" The answer: Despite the filter fineness this route is the easiest The long lubrication circuit with all its little canals requires a pressure of approx. 3 bar; the TOP OEL®-Filter requires less than 1 Bar. To ensure that not too much oil enters the filter, the TOP OEL®-Filter has even been calibrated (inlet diameter 2mm, outlet diameter 1.5mm). Also, because of the counter pressure this creates, no reduction in the normal oil pressure will take place when using the TOP OEL®-Filter (moreover, a normal oil pump has an ample over-capacity, up to 8 a 9 bar). CHAPTER 3 - LUBE OIL ADDITIVES In this chapter we will successively review: 3.1 Composition of lube oil 3.2 The cleaning dope 3.3 The TOP OEL® effect 3.1 COMPOSITION OF LUBE OIL In modern lube oils, additives - also called dopes - play an essential part. Often more than 10 different materials are added, each of which has its own task. 3.2 THE CLEANING DOPE The most important and most commonly used additive is the so-called cleaning dope. Its task 1s to prevent clotting of soot particles in such a way that they remain "floating". This 1s necessary to slow down the viscosity increase and sludge formation. Often this dope -is a base and therefore it also functions as an acid neutralizer. The chemicals which can be used as cleaning dope are the so-called dispersants or detergents. They function in the following way: Dispersants are polar. They consist of one oleophilic pole (likes oil) and one oleo phobic pole (scared of oil). The oleo phobic pole - the small round circles in the drawing - will attach itself to the soot particle to avoid contact with the oil. Whereas the oleophilic pole will behave -in an opposite way. This results in a kind of ring around the soot particle which looks like a pin cushion which prevents further clotting (steric hindrance). The soot has been "dispersed". Detergents accomplish the same result in a different way. The detergent -is electrically charged. As soon as it has formed a film layer around the soot particle it will reject equally charged soot particles. The soot has been "deterged". Once the dispersant or the detergent has attached itself to the soot it is tied up and unable to function further. Hence, after some time these additives will be exhausted, leaving the oil unprotected. 3.3 THE TOP OEL® EFFECT By thorough filtering of the oil, the cleaning dopes are spared. Since the soot has been retained in the filter the dope cannot attach itself and therefore remains active. Of course not 100% of the dope is spared. The explanation for this is as follows; a soot particle - is only fully surrounded - if, say, one million dispersant molecules have attached themselves. Before this happens the soot particle has normally been retained by the filter. However, in one case the soot particle is retained at a time when only a few thousand dispersant molecules are attached and in another case after several hundreds of thousands dispersant molecules are attached. On balance, however, the dope reserve will remain intact much longer when microfi1tration is applied. Thus helping to keep viscosity, acidity and sludge formation in check. Note: After the soot particle has been retained by the filter hardly any dopes will attach to it because - although naturally a constant flow of oil passes through - the soot particle is almost totally "wrapped" by the filter paper. The same mechanism applies for example to the anti-oxidants. This dope neutralizes the radical (further reacting) intermediate products of the oxidation chain reaction by binding them chemically. This slows the oxidation process down. The TOP OEL®-Filter reduces oxidation by retaining the catalysts of the oxidation process (iron and copper) as well as retaining radical oxidation intermediate products, (see chapter 2, sub 1). As a result of this delayed oxidation by microfi1tration the anti-oxidants will be spared. Sometimes the question is asked "does the TOP OEL®-Filter also retain the additives and thereby become counter productive?" No, in fact this is totally excluded. The size of moat dopes is several hundred times smaller than 0.5 micron. It’s the same as if you try to filter out sugar out of a cup of coffee. CHAPTER 4 - SUMMARY; INFLUENCE ON OIL CONDITION The decisive criterion for determining when an oil change is needed, is the oil specification. As long as the oil is within its specification boundary values, it is fit for further use. Microfiltration is only useful if it keeps the oil within the specification on all measure points. Therefore the chemical and physical processes must be kept under control. The preceding chapters have shown that the TOP OEL®-Filter in fact has this abi1ity: * Contamination: is both qualitatively (maximum size of the particles) as well as quantitatively (the number of particles) reduced. * Increase in Viscosity: this remains limited due to the retention of the insolubles, such as soot, and by reducing oxidation. * Oxidation: this is reduced due to the retention of the oxidation catalysts (iron and copper) as well as the radical oxidation intermediate products. * Acid formation: will be restricted by: - absorption of water, this slows down sulphuric acid formation - absorption of liquid acids - slowing down oxidation which slows down development of acid oxidation products - soot filtration which saves basic (cleaning) dope. * Exhaustion of additives: this process is slowed down due to: - retention of soot: sparing the dispersants/ detergents - reducing oxidation: sparing the anti-oxidants - reducing acidification: sparing the base dopes which maintain the anti-acid reserve (TBN). Both scientific as well as practical tests have demonstrated that oil change intervals can be lengthened significantly through the use of the TOP OEL®-Filter. How long the interval periods can become is dependent on operating conditions. The 150,000 km or 2,500 operating hours are a general indication. It may be simpler to use one year intervals as a guideline. The Technical University of Aachen performed duration tests of over 300,000 km and Perkins Engines of up to almost 8,000 operating hours. When a truck drives for example 160,000 km per year, an annual change interval period can therefore be easily recommended. Particularly -in the testing phase the oil condition should be monitored by oil analysis (Lubri-Sensor, now a days called RNC followed by laboratory tests). The research done by the Technical University of Aachen lasted more than 10 years. The graphs in the brochure thus reflect many studies on numerous engines: It can be seen that the TOP OEL®-Filter keeps the oil with-in -its specification boundary values (4X pentane -insolubles, 135% viscosity) much longer than the full flow filter. Measurements of independent polluters such as wear metals, silicon or soot show the same picture. It is noticeable that the large differences only show clearly after a longer period (approx 15,000 km). This needs to be taken into consideration when test results are being evaluated. After an -initial increase the TOP OEL®-Filter establishes a type of equilibrium where after the oil condition remains practically stable (The topping up of new oil obviously has an impact). Research into the pattern of the TBN value proves the chemical effect of the TOP OEL®-Filter: Without the TOP OEL®-Filter the TBN fell from 7.5 to approximately 3.5 after 35,000 km. With the TOP OEL®-Filter the TBN was still measured at 6 after 50,000 km. Also interesting is the influence of a cartridge change on the measurements as illustrated in the graph below in the case of iron. CHAPTER 5 - IMPACT ON ENGINE CONDITION In this chapter we will successively review: 5.1 Abrasive engine wear 5.2 Engine contamination 5.3 Bore po1ishing 5.4 Other wear effects 5.1 ABRASIVE ENGINE WEAR The contamination of the lube oil with relatively large (3 – 15 micron) and hard metal and silicon particles causes scraping and scratching of these particles against primarily the piston and cylinder linings. This is called abrasive wear. An extreme example: The TOP OEL®-Filter consistently filters these particles from the oil and therefore effectively fights this kind of engine wear. The particles of 1 micron and smaller which may go through the filter hardly cause damage since the lube oil film is over 1 micron thick. 5.2 ENGINE CONTAMINATION Contaminated oil also contaminates the engine Particularly so when the cleaning dopes are exhausted. Then many more soot flakes are formed, resulting -in a black sludge which will subsequently deposit itself on vital engine components. The problem of black sludge deposits is today regarded as engine enemy number 1. The formation of these deposits can be shown schematically as to 1 lows: The oil oxidation products and the sulphuric acid form resins which mix with soot (and water), leading to deposits on engine parts. A very serious example of this is the Perkins Engine which is shown in the brochure. The TOP OEL®-Filter largely prevents this kind of engine contamination. The soot is retained in the filter, sulphuric acid and water are absorbed and oxidation is seriously reduced, thereby minimising the build-up of black sludge right from the start. The Technical University of Aachen has established a cleanness rating on the basis of an existing DIN norm for the piston and the groove behind the first piston ring as shown in the foiling diagram; Measurements were taken after 35,000 km for full flow filtration (HS) and after 70,000 km for the TOP OEL®-Filter which implies that the results for TOP OEL® should actually be doubled. It is apparent that the tremendous influence of the TOP OEL®-Filter on the cleanness of the engine is specifically noticeable behind the piston rings. 5.3 BORE POLISHING Engine contamination -in the combustion chamber causes bore polishing. Bore polishing is the local and irregular "polishing" (grinding out) of the cylinder lining as illustrated below. It is evident, that bore polishing is very damaging. It affects the sealing between piston and cylinder lining and leads to lose of engine compression. Bore polishing is caused mainly by deposits in the piston ring groove which limit the tolerance of the piston ring, thereby causing the piston ring to start "polishing", thus steadily eroding the surface of the cylinder linings. It goes without saying that bore polishing is limited by the TOP OEL®-Filter as it results in a cleaner engine and specifically so behind the piston rings. Bore polishing, however damaging, -is the most common, normal wear of the cylinder lining and engine constructors often use this as a norm (e.g. The Ford Tornado bore polishing test). The Technical University of Aachen has demonstrated the correlation between engine contamination and bore polishing: The graph illustrates the relationship between bore polishing and the cleanness rating of the 1st piston ring groove (Kolbenbewertung 1. RN). The better the cleanness rating, the less bore polishing occurs. A similar relationship of course exists between bore polishing and insolubles in the lube oil (Zunahme Koksrückstand): The higher the content of insolubles, the more bore polishing occurs. The research at the Technical University of Aachen has also shown a clear difference in bore polishing and cylinder wear between engines with and without the TOP OEL®-Filter. The above measurements represent the average of many engines after 170,000 km. The conclusion -is that the TOP OEL®-Filter reduces wear of the cylinder lining by about 40%. The same is true for the wear of the piston rings. 5.4 OTHER WEAR EFFECTS The deposits on engine parts also hinder a good heat discharge. Therefore it -is very important that in modern engines, which have to operate at higher temperatures, the engine and the lube oil are kept clean. The bearing areas are sensitive to corrosion. Corrosion is reduced by the TOP OEL®-Filter because it absorbs water and acids. A number of research studies performed for SAE in the USA also conclude that engine wear is significantly reduced by improved filtration (these reports can be obtained from TOP OEL®). Not only does improved filtration lead to a longer, economical lifetime of the engine, it also reduces loss of compression resulting from bore polishing. Therefore, better fuel economy, reduction of oil consumption as well as improved performance during the engine's lifetime are obtained. Although no directly related scientific research has been done, it is to be expected that the normal increase in oil consumption with the ageing of the engine will be reduced by the introduction of the TOP OEL®-Filter. In order to form a general impression of the impact of the TOP OEL®-Filter on the wear of the different engine components it is advisable to read the Perkins Report. CHAPTER 6 - PERKINS REPORT CONDENSED COPY Perkins Engines Limited - Advanced Engineering Report Title: Inspection of 4.203.2 - 7900 hrs without oil change Purpose: To assess the effect on component condition of not changing the lubricating oil over 7900 hrs service operation in a dark fork lift. Introduction Perkins Germany reported that 8 dark fork lift trucks with Perkins 4.203.2 engines fitted, working in a Steel Forging plant on lease hire, had completed 6000 to 8000 hrs without an oil change. One of these, which had completed 7900 hrs, was returned to Perkins Engineering Division for examination to assess the effect of not changing the oil on component condition. The engines had been fitted with bypas filter Type III bypass oil filters with a capacity of 2 litres. The bypass filter element was changed every 500 hrs and the main, full flow, filter every 1000 hrs - the oil remaining in the bypass filter bowl was not drained. The oil used was a 15W40 to MIL-I-2104C specification (turbocharged oil) supplied by Fuchs, a German oil company, which incidentally is approved by Daimler Benz on page 227.1 of their oil recommendation book, which in the oil industry is the seal of approval. Oil analysis was made by Fuchs, which showed the oil to be in good condition, according to Perkins Germany and, in addition, oil condition checks were made using a RNC Typ 3, a device assessed and recommended by Advanced Engineering. Inspection of Components The engine was stripped in Perkins Engineering workshops, measurements of appropriate parts taken, all components were examined for condition and photographs taken. The first impression was that the engine could not have run for as long as 7900 hrs. The general cleanliness in terms of lack of sludge deposits were associated with a much shorter service period and indeed the condition of many of the components supported this view. The following details the condition of each component, with comments, as shown in the order of the attached photographs. Cylinder Head Photograph no. 1 shows the condition of the tappets, in the cylinder head. Valve Mechanism The condition of the inlet and exhaust valves was satisfactory - no wear on stems or seats, with only moderate carbon deposits on the valve heads - the valve stem seals were still flexible with no sign of ageing. Some wear (0,05 mm) had taken place on the rocker shaft in the loaded area of the rocker lever bush, but was considered very low for this service life. This is a boundary lubricated area and wear always looks worse than the actual dimensional checks reveal. The rocker lever bush shows heavy contact marking as might be expected, but again the wear was minimal. The contact pads of the rocker levers, against the valve tips and the tappets showed no wear. The crankshaft was in good condition. CHAPTER 6 - PERKINS REPORT Gears All the gears were in good condition with no apparent wear. The flanks of the teeth on camshaft gear showed surface pitting which is typical of the loaded area on a cast iron gear. The bearing faces of gear bushes showed them to be in perfect condition. Piston, Rings and Liner The pistons were in very good condition with only moderate carbon formed in the cop ring groove and the odd surface tear generated from the top land. Radial wear on the top rings was low at 0.03 mm but they had some wear on the bottom face (0.11 mm), due to combustion gas loading. The liner condition was good with a moderate wear of 0.03 mm at the top ring reversal position, but over the ring belt travel the honing marks were still evident. The condition of the small end bush was very good with very little contact marking. Crankshaft and Bearing The crankshaft was in very good condition with no wear on the journals. The mains and big end bearings were virtually unmarked, again no wear had occurred. Seals The front and rear seals were not worn and were still flexible. The seal on the oil pump had been compressed into the wedge shape of its sealing recess and was hard and brittle. Main Filter Element The filter element was very clean with no contamination - the metal sliver seen in the photograph is residue from cutting the metal canister open. Comments The condition of this engine, related to oil, is presumed to be due to the use of a bypass oil cleaner, which, it is assumed, cleans the oil and removes the minute dirt particles (below 20 microns), which over this service period of 7900 hrs could lead to excess wear. Conclusions The evidence of the general engine cleanliness and good component condition gives prima facia case that the use of a bypass oil filter and high quality oil can give a long service life with no oil change in this type of application. Recommendations Service life on the other fork lift trucks should be monitored and additional oil analysis and filter condition provided. 5th October 1984 ED/AE/DN/5369 CHAPTER 9 In this chapter we will successively review: 9-1 Criteria for the evaluation of micro filters 9-2 Different kinds of bypass microfi1fcers 9.1 CRITERIA FOR THE EVALUATION OF MICROFILTERS The advantages with regard to engine wear and oil change intervals apply more or less to all good bypass microfi1ters. In all brochures of competitive filters the same arguments are put forward, but for a strict comparison it is the filters themselves that count. For an evaluation of bypass microfi1ters the following criteria are important: * Filter effectiveness: It is essential that all oil, which flows through the filter, be actually being filtered. In other words: there should be no internal oil leakages. The construction of the filter has to be such that a11 oil must pass through the cartridge. It is evident that filters through which oil can pass without being filtered are not effective. * Filter retention value: 80% to 90% of the contaminants to be filtered are between 0.5 and 2 micron. Filters with a retention value of over 2 micron are not genuine microfi1ters. * Absorption of fluids: This is required to reduce chemical ageing (acidification) of the lube oil as well as sludge formation. * Cartridge change interval: Should be at least as long as the shortest maintenance interval. The longer the change interval the more economical the filter will be in use. * Compact size: The filter housing must be as small as possible. This is important for easy installation as well as economical use. The larger the filter housing the more oil is required for topping- up. * Pr ice: The relationship between price and quality is always important, as well as the payback period of the initial purchase and installation cost of the filter. 9.2 DIFFERENT KINDS OF BYPASS MICROFILTERS To our knowledge some 15 brands of bypass micro filters are marketed worldwide. These can roughly be divided into 4 categories: * A. Depth and surface type filters These are filters with a cartridge of fibre or cotton wads, or alternatively a cartridge of star-shaped pleated paper in a perforated tin casing. Example: Luberfiner. These filters almost always have insufficient retention properties, are unable to absorb fluids and are everything but compact. * B. Adsorption filters with axial flow The cartridge of these filters consists of a tightly wound paper roll, the height of which is about the same size as its diameter. The oil flows alongside the paper layers from top to bottom. Example: Kleenoil. The disadvantages of these filters are insufficient filter effectiveness as well as an uneconomical cartridge change interval: * C. - TOP OEL® Adsorption filter with radial flow Here the paper roll has an oblong form called a filtration stick and the oil flows through the paper layers from the outside to the inside. Contrary to filters with an axial flow this system has no internal leakages since the sealing of the top and bottom of the filter cartridge poses no problem. Furthermore, the filter surface area, and therefore the cartridge change interval, is several times larger whilst the filter itself remains more compact. This is because the surface area of radial flow filters extends itself to all sides of the cylinder, equalling the perimeter multiplied by the height of the cartridge. In comparison with depth and surface type filters, the advantages are better retention values, the liquid absorption capacity and the compact size. The TOP OEL® - Filter, an adsorption filter with radial flow, is the only filter that actually meets all criteria. * D - Centrifugal filters The principle of centrifugal filters is based on the centrifugal force. The oil flows into a chamber equipped with a rotor that separates the oil from insolubles, which are pressed against the chamber wall where they are deposited. After a period of time the deposit layer has to be removed when the filter is cleaned. Example: Glacier. - Filter effectiveness: Filters with axial flow are sensitive to internal leakages. Since the oil flows from top to bottom the space between the walls of the filter housing and the filter cartridge must be sealed. However, for changing the cartridge some space is required in the very same area. This space is many microns wide and oil will always leak through, leaving the filter without having been filtered. - Cartridge change interval: The change interval of an adsorption filter solely depends on the filter surface area. With normal oil pressure in the engine, dirt particles (of the relevant sizes) will only be pushed into the paper mass up to 15mm to 20mm before the filter is plugged. Hence the filter depth is given (unless the filter is not a micro filter at all), leaving the surface area as the only variable. The larger the surface area, the more particles can be adsorbed and therefore the longer the change interval of the filter will be. - The filter surface area of axial filters is determined by the diameter of the cartridge. Since this is relatively small, the cartridge will soon become saturated with dirt and must be changed quite often. In case the cartridge change interval for axial filters is relatively long, say 25,000 km, this indicates that the filter is no good. (Filter effectiveness.) An advantage of centrifugal filters is that they do not require cartridges. However, these filters are less suited for bypass microfiltration. The centrifugal force is only strong enough to separate the insolubles from the oil at relatively high oil pressures of 3 Bar to 4 Bar. In practice this means that such systems only work at high r.p.m.-s. Furthermore, only the bigger and heavier particles are separated, leaving the smaller particles remaining in the oil. Nor do centrifugal filters have an impact on materials with lower specific gravity than oil. Water and acids are not removed. The Technical University of Aachen also studied centrifugal filters. Of all the types of filters tested, the centrifugal filter scored the lowest, both on oil condition and engine cleanness. The Technical University of Aachen pointed out that centrifugal filters are unable to filter small-dispersed particles. Centrifugal filters are best used when not connected to the engine. On large ships centrifugal filters are used under pressure of a strong pump to clean large reservoirs of oil. However, this is a process of oil recycling rather than bypass filtration in a running engine.