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The Greenleaf filter uses an original wash and filtration regulation system. This gravity filter uses its filtered water output to wash itself and does not require any wash make-up water except when insufficient filtered water is available. The filter can be backwashed using water only (35-50 m · h–1) or using air and water simultaneously (air: 30-55 m · h–1; water: 24-60 m · h–1), or air followed by water (air: 30-70 m · h–1; water: 35-50 m · h–1).
The Greenleaf system’s main component is its distribution and central regulation unit used to control four cells. Cells can be circular (steel or concrete), square or rectangular (concrete).
The water to be filtered (figure 15) is fed into the central unit via an annular distribution channel (1).
Each cell’s inlet siphon (2) feeds water to be filtered into the inlet chamber (3) equipped with an equal distribution weir (4). These constant level inlet weirs replace flow filter rate controllers.
The filtered water is collected in the chamber (5) that is common to all filter cells. The filtered water leaves this chamber over a weir (6) that constantly applies a positive head to the filtering media (12).
When the maximum level is achieved on one cell, a backwash is activated: the cell’s inlet siphon (2) is unprimed by valve (7) opening. The water level then falls back to weir level (6). The remaining cells continue to operate.
When valve (8) closes, the washing siphon (9) is connected to the vacuum chamber (10). Therefore, water rises inside the siphon from both the wash water collection tank and from the filter’s central column, until the system is primed.
The wash water, supplied from the general filtered water tank, then backflows through the filter media and is collected by a trough (11) before passing through a siphon (9) for discharge to the drains (13).
When the filtering media is clean, the siphon (9) will be unprimed as valve (8) opens. The «filtration» phase is resumed when valve (7) closes and the inlet siphon (2) is once again primed.