Patent ID: 6966980

Claim:
A slow sand filter for filtering water comprising: (a) a linear, polyethylene filter vessel comprising (1) a top, a bottom, and a peripheral wall extending therebetween, said top comprising a removable lid, (2) at least one sand filtration layer position in a lower portion of said vessel and an inlet chamber in an upper portion of said vessel, a top surface of said sand filtration layer defining the lower boundary of said inlet chamber, (3) an inlet, an outlet, and a cleaning outlet in said peripheral wall above said sand filtration layer; (b) a detachable indicating and flow control assembly for simultaneously measuring pressure head loss and regulating flow through said outlet, said assembly position exteriorly of said vessel and comprising (1) an end coupled to said outlet and a fixed orifice spaced from said end, said fixed orifice being of a size consistent with a desired slow sand filtration rate; (2) a vertically-extending, transparent piezometer tube fluidly communicating with said assembly and having a first end position downstream of said outlet and upstream of said fixed orifice and a second end proximate said vessel top for visually indicating in said filter, said assembly providing an anti-siphon function for said outlet, said fixed orifice being positioned above the level of the sand layer top surface that no more than 12 inches of head pressure is applied against the fixed orifice in a normal filtration mode; (c) a filtered water collection assembly comprising (1) a perforated portion adjacent said vessel bottom for receiving water filtered in said sand filtration layer, and (2) a riser pipe extending through said sand filtration layer and fluidly coupled between said perforated portion and said outlet; and (d) a valve coupled to said cleaning outlet for draining supernatant during harrowing of the sand layer top surface, when cleaning is necessary as indicated by a water level in said piezometer tube.