Fuel filters trap contaminants in fuel, oil, diesel oil and even in LPG installations, providing efficient protection to precise elements of the I.C engines fuel systems from quick wear. These fuels contain contaminants resulting from the production process and distribution. Dust, soot from outer tank surfaces, water and microorganisms may cause quick wear of injectors, pumps, or pressure-regulating valves in modern engines. Therefore each fuel system has filters which are optimally selected according to engine requirements, fuel quality and expected exploitation conditions. Requirements for filters are very high. The filtering for modern engines is required for contaminants particles size 3 ÷ 5 μm with over 90% efficiency. For better performance, more than one filter is installed in the fuel system in many cases. However in comparison with oil filtration, there are no by-pass valves in fuel filtration which clear the fuel flow, when the filters are clogged, as it is a rule that only clean fuel goes into the combustion chamber. Therefore it is better that the engine stops due to lack of fuel (dirty filters) than if it had to work using non filtered fuel.