Glossary of Liquid Filter Media Terms
BLINDING: The loading up of the filter medium so as to reduce filtration efficiency.
BREAKING STRENGTH: Average force required to break a test specimen by tension.
BURSTING STRENGTH: Force required to burst a standard specimen/ the ability of a material to resist rupture by pressure.
CAKE: The layer of solids deposited on the filter medium during the clarification of a slurry.
CAKE RELEASE: Ability of a filter medium to allow clean separation of the cake from the medium.
CALENDERED CLOTH: Cloth that has been passed through a pair of heavy rolls to reduce the thickness of the cloth or to flatten the intersections of the wires and provide a smooth surface. The term “rolled” is often used.
CHAIN WEAVE: A compact, heavyweight weave’made with plied yarn in both directions; identified by pattern of two-up and two-down broken twill, two ends of right hand and two of left hand, repeated on four threads each way. Although its tensile strength may be low, it affords both high filtrate clarity and high flow rates.
COUNT: This expression has two meanings, the size or number of a yarn, and the number of warp and fill yarns per inch in a woven fabric. The filter operator generally uses the latter terminology.
CROWFOOT SATIN WEAVE: A one-up and three-down broken twill with two ends to the right and two ends to the left.
CYCLE: The actual interval of filtration, expressed in units of time, e.g., hours or days.
DENIER PER FILAMENT: Weight in grams of a single continuous strand of yarn 9,000 meters long. For each material, the dpf. is proportional to the cross-sectional area of the filament.
DENSITY: Ratio of weight of a medium to the weight of an equal volume of fiber.
DIMENSIONAL STABILITY: The ability of a fabric to retain its original dimensions.
DISCHARGE: The liquid that leaves the filter after passing through the filter medium. May be different from filtrate, e.g., wash water discharge.
DOCTOR BLADE: A blade used to maintain the thickness of the cake, or precoat, by trimming it down at certain intervals.
DRILL WEAVE: Name applied to three-harness, warp-face twill weave, the two-up and one-down twill effect. Little used in filtration as it is usually somewhat more expensive than twill, yet has about the same filtering characteristics.
DUCK: This covers a wide range of the most durable fabrics made. Closely woven and heavy, the most common are number duck, army duck, and flat or ounce duck. The number and ounce ducks are most often used in liquid filtration in the process industries.
ELONGATION: The deformation caused by a tensile force, expressed as a percentage of the original length.
FELT: A fabric built up by the interlocking of fibers by a combination of mechanical work, chemical action, moisture and heat.
FILLING OR WEFT: The yarn that interlaces with the warp yarn to form a woven fabric. The filling runs from selvage to selvage at right angles to the warp.
FILTER AID: A substance of low specific gravity so that when mixed with the liquid to be filtered, it remains in suspension. It should be porous and must be chemically inert to the liquid being filtered. It increases filtering efficiency.
FILTER MEDIUM: A porous sheet capable of passing liquid’through while retaining solids by means of mechanical separation.
FILTRATE: The fluid that has been separated from the solids in the slurry being filtered.
FRAZIER PERMEOMETER: A porosity testing device. The normal measurement is the ai flow in cubic feet per minute passed through one square foot of fabric at 1/2-in. water pressure. Fabrics with ratings of 1-10 cfm. are considered very tight whereas cloths that test at 450-500 cfm. are extremely porous. The test is used on woven and nonwoven materials.
GURLEY PERMEOMETER: Porosity test device used on tightly woven cloth or on filter papers. Ratings are given in the number of seconds taken for 300 cc. of air to pass through one square inch of material at 124 mm water pressure.
HONEYCOMB OR WAFFLE WEAVE: Pattern of these fabrics resembles the cellular comb of the honey bee; is used for drainage cloths beneath the regular filter cloth.
LEAF: A filter component used for supporting the filter medium.
LENO WEAVE: A lightweight, open-mesh cloth; certain warp yarns are passed from side to side of one or more ends and are bound in by the filling in this position.
MESH: Number of openings, or fractions of openings, in a lineal inch of cloth. Where the fractional part of an inch is specified, for example 1/2 mesh or 1/2-in. mesh, the term is understood to mean the measurement from the center of one wire to the center of the adjacent wire. The term “mesh” should not be confused with clear openings or space.
MONOFILAMENT: A single, large continuous filament of a synthetic fiber.
MULLEN (BURST TEST): Force needed to burst a given area of paper or cloth, under fluid flow conditions, and expressed as the pressure in inches of water that will burst a two-in.-dia. test specimen.
MULTIFILAMENT: A yarn having two or more continuous monofilaments.
NAP: The fuzzy, fibrous surface of a cloth produced by scratching the surface so that some fiber is raised from the body of the yarn.
PADDOCK OR DRAINAGE CLOTH: Open-mesh, coarse yarn fabrics, knit, leno or simple woven types for support of paper or closely woven fabrics. They provide depth for ( drainage and/or support to prevent media breakage of solids buildup beneath the media.
PERMEABILITY: The rate of flow of fluid under a differential pressure through a material. Air permeability measurement provides a convenient comparison for various media and indicates the construction requirements for specific particle-size retention. As a rule of thumb, lower permeability values indicate finer particle retentivity.
PICK: One strand of the filling.
PLAIN WEAVE: The simplest and most common weave, repeating pattern on two warp and two filling yarns. Also known as a “one up and one down” weave.
PLY: The number of individual yarns twisted together to make a composite yarn.
PRECOATING: The operation of depositing on inert material (filter aid) prior to beginning filtration.
PREFILT: One of the names used to describe the mixture of solids and liquid prior to filtration.
RECTANGULAR MESH: Woven cloth with a different mesh count in the fill than in the warp. Sometimes called “oblong mesh” or, in the case of finer meshes, “off-count.”
SATIN (OR SATEEN) WEAVE: A smooth fabric surface produced by carrying the warp (or filling) uninterruptedly on the fabric surface over many filling (or warp) yarns.
SHUTE WIRES: See “fill wires.”
STAPLE: In natural fibers this expresses the length of the fiber. In a synthetic, it signifies filaments that have been cut to the length of natural fibers. Spun yarns are made by twisting short staples together.
SQUARE MESH: Mesh count that is the same in both directions.
TWILL WEAVE: A pattern of diagonal or “twill” lines running upward to the right(or left) of the fabric face. They offer high flow rates and abrasion resistance C qualities.
WARP: The yarn that runs lengthwise in cloth as it is woven on a loom.
WET STRENGTH: The strength of the filter medium when saturated with water. It can also refer to the property obtained when an additive is imparted to filter paper to give it additional strength when wet.