Dirt in fuel causes poor engine performance and prevents normal operation of fuel pump and carburetor. The fuel is filtered when it enters the fuel tank. In some cases, it is again filtered in fuel pump. A separate fuel filter is also connected between the fuel pump and carburetor. It serves to catch any water or unit. The fuel will enter the glass bowl from the inlet and passes through the ceramic filter. It separates the foreign particles. The water and sediments are collected in the bowl and removed during cleaning.
DIESEL FUEL FILTERS :
Fuel filters are used before the fuel enters the fuel injection pump and injectors. The plungers and barrels of the injection pump , needles and nozzles of the injectors are made with close tolerance. Even a very minute dust will wear these parts. It is , therefore , quite essential that the fuel should be well filtered before it is fed to injector pump and injectors. Hence two filters are used for filtering diesel. They are primary filter and secondary filter.
i) Primary Filter ( Pre Filter ) :
The primary fuel filter removes water and coarse dust. Generally, sedimentation type is used. It has conical diffuser and sediment chamber.
The fuel enters the filter and flows around the conical diffuser funnel to accelerate downwards to the sediment chamber.
As the impurities are heavier, they move downwards and settle down due to slow movement of fuel in the chamber. Then the settled impurities are drained off periodically.
ii) Secondary Filter :
The secondary filter is fitted after the feed pump and it separates out abrasive particle and any water in the fuel. These filters have elements of impregnated paper, ceramic metal disc and fiber . The fine pores of the filter element retain the minute particles except water droplets which are forced through element.
However, as they have passes the element , electrostatic attraction produced by the resin impregnated element causes the droplets to be pulled towards each other and continues to form larger droplets. Since the droplets are heavier, they are settled down in the chamber.
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