Seawater coarse filtration strainers remove larger particulate matter from the feed stream to the SRU plant. The flow of water through the coarse strainers is set by the downstream demand.
The coarse strainer packages consist of self cleaning automatic backwash filters. The filters will backwash automatically either according to a time interval or high differential pressure. Backwash water is taken from within the cleaned water compartment of the vessel and reverses flushes each of the elements in turn. The backwash effluent passes through the element to a closed drain header.
Filtration with coarse filters can typically range from less than 50 microns to 2000 microns. Filter cleaning is accomplished using automatic backwashing, and is required when the differential pressure on the unit increases to the point of maximum or the flow becomes too restricted. Many units limit backwash volume and can be cleaned on-line.