The prime duty of oils used in engines are:
-To ensure lubrication of the movable parts of the engine.
-To prevent friction losses and wear
-To prevent accumulation of carbon wastes
-To ensure cooling of the pistons
-To neutralize the combustion acids formed during the combustion and minimize the wear these acids cause.
Oil filter keep the contaminated oil and particles formed because of abrasion during the operation of the engine away from the engine and transmission. Carbon grains, dust and dirts can mix to oil during the operation of the motor. A portion of these foreign matters precipitates to the casing and are held by the oil strainer and cap magnet. Smaller grains are strained by the filter before they are mixed with oil and hence harm to the system is prevented. Oil filter, which is one of the most important parts of motor greasing system, is the place where the dispersing additives in motor oil accumulates the corrosive and harmful matters in the motor out of the casing. Oil filter is present in all internal combustion engines. Both for life time of the motor and the filter, care must be given to use appropriate oil for the motor and appropriate filter for this oil. Also oil temperature is very important for an effective filtering.
The main reasons of contamination:
-Solid particles reaching to inside of the cylinder from air and fuel.
-Wastes that ar formed because of friction in rotating components.
-Water and carbon wastes that are formed during the burning of the fuel.
-Accumulations formed with burning and contamination of the oil.
Oil filters are important parts for the lifetime of the motor. Especially in high power and speed applications, for the motor to work efficiently, the oil in the system should circulate at the required speed and amount. The oil completing the circulation returns to the tank of the vehicle and is sent to the greasing channels again by a pump. When it comes to oil circulation, characteristics of the oil filter and the filtering element are very important. Elements in the oil filter are composed of special papers and has property to hold small particles. If the filtering element and its characteristics does not answer the oil need of the motor, there can be many problems about efficient working. If the pore size of the filtering element is larger than required, foreign particles in the oil can cause cloggings in the oil circulation system. In this case the motor is not greased enough and big breakdowns like gasket burn, bearing wrapping and crank cut can occur.
Also these particles which enter the motor without filtration can cause scratches on the motor shank. Again as the filter does not filter enough the motor oil will be contaminated before its acceptable lifetime, oil replacement will be needed while the filter is not contaminated yet and this will bring extra cost. If the pore size of the filtration element is smaller than required, the oil filter will be contaminated before its normal lifetime and it will be necessary to replace it. When the user does not realize this (because the filter will be contaminated before the oil change period of the vehicle), there can be some breakdowns in the motor. In addition to filter paper, some critical parts of the oil filters also play important roles in the filtering process. Return system ensures that oil always exists in filter in oil filter mounted to downwards. By means of this system, motor is not kept without oil during initial operation. Hence possible breakdowns are prevented. By-pass system is usually special to oil filters. When the filter paper is contaminated and clogged, oil cannot pass through filter paper and oil pressure in the filter increases. When the pressure reaches by-pass spring pressure it is opened and oil is sent to motor block. Here, the spring used in the system should be chosen correctly.
If a spring with low opening pressure is chosen, oil passes through the by-pass system without straining before the filter is clogged and can damage the engine. If a spring with high opening pressure is chosen, when the filter is clogged, the motor can be kept without oil until the inner pressure of the filter reaches to spring opening pressure and can be damaged. The only drawback in this system is the motor passing through the by-pass system is sent to the motor without filtration. In this case small particles can enter the motor and can cause extreme scrathing and abrasion. For this reason the oil filter should be replaced when the time comes. In maintenance instructions of vehicle producer firms, the replacement periods of filters are given. When a suitable filter is used for the engine, oil replacement and filter replacement become simultaneous. The general application in the market is this way. Also sheet metal elements of filter like busing, ring and cap should be suitable for the filter working conditions. For example the strength of sheet metal components to filter working pressure should at desired level. The surfaces of sheet metal components should be protected against corrosion and their interconnection should be made properly. The gaskets used in the filters are also important parts for impermeability. The gaskets should be resistant to pressure, temperature, vibration and characteristics of the straining material. Especially if upper gaskets are not compatible to the portion where the filter is connected to the motor, it causes oil loss in the system and this situation can cause important damages. Hence the inner structure and the dimensions of the gasket should be at desired values. The outer part of the filter where it is mounted on the motor (G) should be in accordance with the standards. Because of the vibration formed during the operation of the motor, the filter can loosen and as a result, impermeability problem can arise. This situation may cause undesired breakdowns. In order to prevent this, the thread size should be check during the production if it is at the measures defined in quality standards and the filter should be tested for vibration. Also in oil and hydraulic filters, inner sheaths can be used to increase corrosion resistance.
If appropriate filter and oil are used;
-A sufficient quality oil layer is formed in the cylinder liner. Hence abrasion of liner and piston rings is prevented.
-Formation of adhesive wastes in piston ring grooves is prevented.
-Bearing wear is decreased.
-Formation of adhesive wastes on cylinder surfaces and valves is prevented.
-All movable parts in the motor are cleaned.
-Re-entering of cast iron particles coming from piston, piston ring and grooves and particles of white metal, brass and bronze coming from gear, cam is prevented.
Filters can be dividen into two basic groups according to their oil cleaning methods:
-Barrier Type Filters: Strain type filter material is used and oil is cleaned by passing through the filer.
-Energic Filters: Contaminated particles and oil are cleaned with the help of gravitation and magnetic forces during motion.
The filters produced today show the characteristics of both types. Based on the structure of barrier type filters, we can divide them into three subgroups:
Filters that can be mounted by rotating: In this type of filters, metal components are more and they are produced as single-piece. The filter is in a body made of stainless steel. They are mounted on the motor with the help of a metric or whitworth fine threaded screw. When the lifetime of the filter is over or when the filter is clogged, it is dismounted and chucked out. This kind of filters have advantages like mechanical strength during use and easy replacement. While the motor oil is being replaced the filter should be dismounted, the gasket of the new filter should be greased first and should be mounted on the motor by rotating.
-Replaceable filters: In this kind of filters busing or mounting spot is ready on the motor and filter is mounted on this spot. Working principle is the same with atom filter and basically their functions are the same but in this type of filters elements can be replaced. Filters used for pre-cleaning of the oils and made of unwoven material or in other words, secondary filters are parts of greasing systems. Filters made of unwoven materials can clean much more material and particles compared to paper filters. This kind of filters are only chucked out when the element filter is clogged. But the excessive resistance they put up against air flow makes them impossible to use in internal combustion engines today.
Nowadays, both these two filters and some other tpe of filters are used. The type of filters to be used in the greasing system of the automobiles is determined during the production of the motor and can vary according to the type of the motor.
We can divide greasing systems into three groups according the position of filters in motor:
-Full flow systems: In this type of systems oil filter is directly connected to the motor. This way, whole oil in the motor passes through the filter. But in this situation, because of the resistance of the filter, the oil flow to the motor is limited and the oil pressure in the motor may decrease. Because of this valves are used in full flow systems. The function of the valve is to speed up the air flow to the motor. This valve may be in the oil filter or the motor.
-Partial flow systems: In this type of greasing systems oil filter is connected to the motor in parallel. This position of filter means that only 10% of the oil in the circulation passes through the filter. The remaining oil (nearly 90%) directly circulates in the motor and greases all systems. In this system cleaned air amount gradually decreases and the filter is clogged.
-Combined filtration systems: Two filters are present in this system and they function as described above. The oil coming from the oil pump passes through the first filter first and then it is divided into two. A large portion of the oil (nearly 90%) directly goes to the motor and the remaining oil (nearly 10%) goes to the second filter to get cleaned. Mounting of two filters to the greasing system increases the efficiency of the greasing and prolongs the lifetime of the filter.
Despite filters that are mounted by rotation look like eachother in appearance, their internal structures are quite different. In the greasing system of the motor, in order to guarantee efficient working of the filters, working parameters should be balanced very well. These parameters are effective cleaning, absorbtion capability, suitable resistance of oil flow, working pressure and structural characteristics of the filters (position on the motor, type of inner valves, sized of filters and gaskets).
According to the structure of greasing systems, three types of valves are used in filters that are mounted by rotation:
-Nippel valved: This valve is a round shaped rubber piece. It is mounted on the outer side of the filter and prevents return of the oil to the oil pump.
-Peripheral valved: This valve always stays in the filter and it is a part of oil supply system. It is used if there are no such valves on the motor. The main function of this valve is ensuring the continuity of oil circulation when the motor is working in cold condition or when the filter is clogged because of excessive use.
There are two types of peripheral valve in filters that are mounted by rotation. The peripheral at the bottom is mounted to the bottom of the filter while the peripheral valve on top is mounted on the top of the filter. Ensuring the circulation of oil over basic filters is amoung duties of peripheral valve. If the circulation is too fast, the accumulated dirty particles will mix to the oil again and contaminate it, and this will result in too quick abrasion of motor. In order to avoid these negative effects, the filter should be opened and cleaned more frequently. The upper valve prevents dirty particles to mix with clean oil. At the same time, if the valve is open, it ease the oil flow through the filter and shortens the way. This way, optimum protection is achieved for motor and dirty particles collected in the filter cannot return to clean oil.
Antisiphon valve: The main function of this valve is preventing the oil to return to the motor from the filter. If the antisiphon valve is mounted in the filter, dry and semi-dry friction of rotating parts of the motor is prevented. This occasion is called “dry operation” and causes the motor to be abraded very fast. The aim here is to minimize the abrasion. The antisiphon valve prevents the motor to be kept without oil while the filter is replaced. Both motor and the environment is protected from contaminated oils this way.
Source: AFM Filtration, manufacturers of Atom brand of filters
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