FERROUS IRON:

A divalent iron ion, usually as ferrous bicarbonate which, when dissolved in water, produces a clear solution. It is usually removed by cation exchange water softening. Also called "clear water" iron.

FILTER: A device that separates solid particles from water by recirculating the water through a porous substance (a filter medium element). Permanent Medium Filter: A filter that utilizes a medium that under normal use will not have to be replaced. Diatomaceous Earth Filter: A filter that utilizes a thin layer of diatomaceous earth as its filter medium that periodically must be replaced. Cartridge Filter: A filter that utilizes a porous cartridge as its filter medium.

FILTER AGITATION: The mechanical or manual movement to dislodge the filter aid and dirt from the filter element.

FILTER AID: A type of finely divided media used to coat a septum type filter, usually diatomaceous earth or volcanic ash. (NOTE: Alum, as used on the bed of a sand filter, is also referred to as a filter aid).

FILTER CARTRIDGE: A filter which operates through a disposeable cartridge. These are of two general types: The surface or area type where the suspended matter is removed at the surface, and the depth type in which the interstices vary from large to small in depth.

FILTER CYCLE: The operating time between cleaning or bachwash cycles.

FILTER DIATOMITE: One designed to filter water through a thin layer of filter aid such as diatomaceous earth or volcanic ash. Diatomite filters may be of the Pressure, Gravity, Suction or Vacuum type.

FLOCCULENT: Chemical which, when added to water, causes particles to coagulate into larger, settleable groupings. Aluminum compounds are common catalysts in this process.

FLOW RATE OR CAPACITY: The volume of liquid that passes a given point in a specified unit of time.

FILTER ELEMENT:

A device within a filter tank designed to entrap solids and conduct water to a manifold, collection header, pipe or similar conduit. A filter element usually consists of a septum and septum support.

FILTER MEDIA: The finely graded material which entraps suspended particles (sand, anthracite, diatomaceous earth, etc.).

FILTER ROCK: Graded, rounded rock and/or gravel used to support filter media.

FILTER SEPTUM: That part of the filter element consisting of cloth, wire screen or other porous material on which the filter cake is deposited.

FILTER, GRAVITY SAND: A filter with a layer of filter media (usually silica sand) supported on graded gravel through which water flows by gravity.

FILTER, PRESSURE SAND: A sand filter enclosed in a tank to operate under pressure. FILTER, SAND: A type of filter media composed of hard sharp silica, quartz, or similar particles with proper grading for size and uniformity.

FLOOR SLOPE: The slope in the pool floor, usually expressed in feet (or inches) of vertical rise in feet (or inches) of horizontal distance

FILTER, VACUUM (SUCTION): A filter which operates under a vacuum or from the suction side of a pump.

FILTRATE: The rate of flow in volume per time (gpm, gph), through the filter system installed per manufacturers instructions with a new, clean filter medium

FILTRATION FLOW: The mechanical or manual movement to dislodge the filter aid and dirt from the filter element.

FILTRATION RATE: The rate of filtration of water through a filter during the filter cycle expressed in US gallons per minute per square foot of effective filter area.

FINA: The Federation Internationale de Natation Amateur The governing body for intercollegiate competition including the Olympic games.

FLANGE: A device used to couple to a pipe on the suction or discharge of a pump.

FLOCCULATING AGENT: A compound, such as one of the alums, which forms minute flakes in water which attract or enmesh small suspended particles.

FLUORIDE: A salt of hydrofluoric acid which may occur naturally in water supplies or be added by municipal processes for the prevention of dental caries. Fluoride is considered toxic in most medical settings and has been implicated with a wide range of physiological disorders including renal bone disease.

FLUIDIZATION: A process by which particles are suspended by an upward flow of liquid, such as may occur during back washing of ion exchange resin or carbon media.