Particulate impurities in fuel are known to be the cause of engine breakdowns and wear problems, particularly with the diesel. A diesel fuel filter, after it is covered with dirt and grit, may stop passing fuel altogether, causing the engine to stop. Also, eventually some of the grit may somehow work its way through the filter, and do considerable damage to the diesel injectors.
There is a need therefore for a fuel system which can be switched from one filtering zone to another so that the engine can be run while one of the filter zones is clogged, and also there is a need for a system which is easily purged and backwashed without requiring the replacement of filter elements.