As fuel moves through a filter, the medium within the filter traps contaminants and particles that are larger than the pores of the filter. This process is known as mechanical filtration, and it's how most filters work to clean fuel. The size of the particles that can be trapped by a filter depends on the size of the pores in the filter media. For example, a 2 micron filter has much smaller pores than a 10 micron filter, so it can trap smaller particles. As fuel flows through a filter, some of the contaminants and particles will become trapped in the media. Eventually, the filter will become clogged and will need to be replaced. The frequency with which you'll need to replace your filters will vary depending on the quality of your fuel and how often you use your vehicle.