Backflushing and Self-cleaning Filters

Most filter elements, including aU of those described in Sections 3K and 3L, are intended to be cleaned free of accumulated contaminants, wherever this is possible, simply from the economic viewpoint of avoiding waste. This is done either by removal from their housings for cleaning in another place, or by cleaning in situ, but only after stopping the flow of process fluid through them. 

Backflushable Alters generally rely on the liquid velocity to clean the filter medium. This usually limits the use of these systems to low viscosity liquids (up to 50cp). While this is generally true, there are applications where backflushable systems operate very well with fluid viscosity as high as 50,000cp. In these cases, fluid velocity is almost certainly not a major factor in cleaning the filter medium. 

Cartridge backflushable systems operate as closed systems. As a consequence, they can be used in applications with toxic or hazardous fluids with a minimum impact on the environment. 

This relationship then gives the area required in terms of the number of square metres required for one hour of operation. 

The area that is determined in this way is only an estimate since some of the parameters used in the above equation are also estimates (dirt-holding capacity and backflushing efficiency). The main ramification of this is that the backflush interval achieved will be different to some degree from that calculated. In some cases, it is worthwhile to refine the basic data used in the equation by recognizing that the actual dirt-holding capacity is usually affected by the forward flow rate, and that the backflush interval can be corrected to account for the on-stream exposure of most filters during a backflush cleaning cycle. 

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