Clarification and Prefiltration
Clarifying filters and prefilters are recommended for removing contaminants that would affect downstream product quality, or otherwise plug a membrane filter and reduce its effectiveness and service life. The economic advantage of extending a membrane filter's life is far greater than the cost of prefilters. Clarifying filters and prefilters are suited for applications where 100% retention of contaminants above a specified pore size is not required. A non-fiber releasing, membrane-like prefilter is recommended when using a clarifying or prefilter as a final filter. Fiber matrix clarifying filters and prefilters may occasionally unload retained contaminants into the filtrate if subjected to shock, such as that caused by a rapidly actuated valve.
Selection of a clarifying filter or prefilter is based upon the retention efficiency required for the filtration process at hand. Choosing the proper nominal pore size for a clarifying filter and/or prefilter will ensure the required dirt-holding capacity in your system. It will also extend the life of the final filter, and provide an economic advantage. In some cases, it is practical to use a moderately efficient clarifying filter followed by a more retentive prefilter. This will allow each filter in the train to be more fully expended, while removing as much incident contamination as possible.