Fluid filtering systems

Claim 1

A fluid filtering system including at least two filter units so arranged in parallel that flow of fluid from a source to a point of usage can take place by way of only one said filter unit at a time, each other filter unit then being out of service, said system also including means for sensing the degree of contamination of whichever one of said filter units is in service so that when the degree of contamination is such that the said one filter unit is no longer in a suitable condition for further filtering service, said means including means for causing the by-passing of that filter unit and the bringing of another filter unit into service, said system further including jet-type back-flushing means which is automatically operable upon its filter unit when so by-passed to effect cleaning of the filter element of that unit, by jet back-flushing in the direction opposite to normal filtering flow therethrough, said back-flushing means being so subjected to the pressure differential subsisting between the unit in service and the unit out of service as to cause that back-flushing means to traverse with respect to its said filter element, and timing means for automatically controlling the period of time during which the jet back-flushing operation is permitted to continue.