Duplex filters comprise two filter housings. One half of the filter is in operation whilst the other clean half is on stand-by.
When the contamination exceeds a preset tolerance level, the flow can be switched to the cleaned half of the filter without any pressure shock. The contaminated filter element is cleaned whilst the plant continues to run. Switch-over is performed by a cylindrical cock valve or double stage three-way ball valves. The design prevents both filter chambers from being shut off at the same time.