Filtration, in a general sense, can be defined as an operation with the aim of separating solids from fluids. It achieves this by a process of interposing a medium through which only the fluid can pass through, blocking the solid particles from passing through. The separation is therefore achieved by some form of interaction between the substance and the filter itself. 

Oil filters are designed with one sole objective in mind – to remove contaminants from the oil passing through them. This oil can take many forms depending on the environment in which the filter is placed, including engine oil, transmission oil, lubricating oil and hydraulic oil. Every time oil circulates, it passes through the oil filter, and so it is a key component. If the filter is effectively designed and does the job it is supposed to do, it will keep the harmful contaminants from damaging the inner engine components, which, in the long term, can save you a hefty bill. 

It also serves a dual purpose – due to the anti-drainback valve, the filter retains a small amount of oil whenever the engine is switched off. 

While the engine is at rest, the oil drains into the bottom of the engine. This means that the moving parts in the upper section of the engine become unlubricated, which can potentially be dangerous when the engine needs to start up again. However, to prevent this, the small amount of oil remaining in the filter due to the anti-drainback valve will circulate quickly into the engine when the engine is switched on, which quickly restores proper lubrication. In essence, a good oil filter ensures that your engine will have a longer component life, ensuring a long and healthy life for your engine.