The function of a media filter is to reduce the level of suspended solids present in the feed water. The unfiltered water flows downward through the filter media bed. Suspended solids become trapped in the media bed and remain trapped until the media bed is backwashed. During the backwash process, the flow through the media bed is reversed, the media bed is fluidized, and the trapped solids are released and flushed to drain. Upon completion of the backwash process, flow is redirected downward through the media bed and flows to drain thereby rinsing the media bed before the filter is returned to normal service.

If an uninterrupted flow of filtered water is required, it will be necessary to utilize multiple filter units piped in a parallel arrangement. This will allow one filter at a time to be removed from service and backwashed while maintaining operation.

The filter vessel is sized to provide the proper flow velocity through the media bed and to provide sufficient "freeboard" for bed expansion during the backwash process. The filter vessel is fitted with the appropriate connections to accommodate the required distribution system components. The media bed is composed of one or more layers of media. The size and density of the media in the layers are selected to provide multi-step filtration in normal operation and proper bed stratification during backwash. The internal distribution system insures uniform water flow through the media bed. The fine openings in the distributors prevent media loss and the V-shaped design of the openings prevents clogging.

In order to provide the required modes of operation, service, backwash and rinse, a means of controlling the valves is provided. For units incorporating a multi-port valve, the valve control is an integral part of the multi-port valve. For units with individual valves, a separate timer/stager or programmable logic controller provides the control. A series of valves, or a single multi-port valve, divert the water as required for the service, backwash and rinse modes of operation. The face piping routes the water from the terminal points through the series of diversion valves and into and out of the vessel.