Screen filters remove relatively small amounts of sands and organic material before clogging and causing a flow rate reduction. Two or more fitters installed in parallel will increase the time between screen cleanings. Screen cleaning can be a manual or automatic operation. These filters are sized based on the equivalent screen mesh fitter size. They also require periodic cleaning.
Some manufacturers provide an automatic back-flush feature.
Wafer filters provide more filter surface area than screen filters of the same size. These filters will remove colloidal, algae and other organic material usually present in surface waters. The size and type of media used determines the degree of filtration. The finer the media, the smaller the particle size that will be removed. Table 1 shows the relationship between sand grade and screen mesh size.