Understanding filtration › Appendices

APPENDIX A

Glossary

Sixty terms from solid-liquid filtration and filter media, each defined in one or two sentences, with a pointer to the chapter that covers it in more depth. Enough to read a data sheet or follow a discussion with a supplier without stumbling over the vocabulary.

Nicolas Ract · 12 min read · October 2026

The terms, A to W

Absolute rating (rétention absolue)

Ability to retain particles of a defined size completely, under standardised test conditions [1]. → chapter 3.3

Air permeability (perméabilité à l'air)

Air flow passing through a new cloth, per unit area, under a set pressure difference; expressed in mm/s, L/m²/s, L/dm²/min or cfm/ft² [2]. → chapter 3.3

Back pressure (contre-pression)

Pressure opposing the flow of filtrate at the filter outlet; if excessive, it can cause leaks between plates. → chapter 4.3

Backing cloth (sous-toile, toile de support)

Coarse, robust fabric placed between the plate and the filter cloth, acting as a mechanical support [1]. → chapter 3.4

Belt filter (filtre à bande)

Continuous filter that separates solids on an endless filter belt [1]; in belt filter presses, the drained product is then pressed between two belts. → chapter 2.3

Blinding (colmatage)

Progressive loss of a medium's open area as its pores become obstructed: the pressure drop rises at constant flow, or the flow falls at constant pressure [1]. → chapter 4.4

Brew (brassin)

In brewing, one complete brewing operation; the natural unit for counting the service life of a wort filtration cloth. → chapter 4.5

Bridging (pontage)

Mechanism by which particles form bridges over the pores of the medium and quickly create a separating layer [1]. → chapter 3.3

Cake discharge (décollement du gâteau)

Ability of the filter cake to come away from the cloth when the filter opens; helped by a smooth surface (monofilament, satin, calendering). → chapter 3.2

Cake filtration (filtration sur gâteau)

Regime in which particles are retained on the surface of the medium; once formed, the filter cake does most of the filtering [1]. → chapter 1.1

Cake washing (lavage du gâteau)

Forcing a clean wash liquid through the formed filter cake to extract soluble impurities from it [1]. → chapter 1.2

Calendering (calandrage)

Finish that flattens and smooths the cloth between heated rollers: smoother face, better cake discharge, lower permeability. → chapter 3.2

Campaign (campagne)

Annual period of continuous production in a seasonal industry, such as the beet campaign in a sugar factory. → chapter 4.5

Candle filter (filtre à bougie)

Filter with cylindrical elements through which flow passes from the outside inwards; the filter cake forms on the outside of the element [1]. → chapter 2.5

CGR plate (plateau CGR)

Abbreviation of caulked and gasketed recessed, a recessed chamber plate: the cloth, fitted with a sewn-in bead, is pressed into a groove in the plate [3]. → chapter 3.4

Chemical washing (lavage chimique)

Cleaning a cloth with an acid or a base to dissolve deposits that water does not remove; to be tested on one cloth first, with a product compatible with the fibre. → chapter 4.4

Cost per tonne (coût par tonne)

Total cost of filtration (cloths, changeovers, washing, filter cake disposal, energy) divided by the tonnes of dry solids filtered. → chapter 6.3

Decitex, dtex (décitex)

Unit of linear density for fibres and yarns: mass in grams of 10,000 metres of yarn [1]. → chapter 3.2

Depth filtration (filtration en profondeur)

Regime that uses a relatively thick medium [1], particles being retained within its thickness rather than on its surface. → chapter 1.1

Disc filter (filtre à disques)

Continuous vacuum filter made up of discs covered with filter sectors that rotate partly immersed in the slurry. → chapter 2.4

Drainage surface (surface de drainage)

Structure that allows the filtered liquid to drain away [1]; on a plate, the area of pips or ribs on which the cloth rests. → chapter 4.1

Dry solids content (siccité)

Proportion of dry matter in the filter cake, as a percentage of its wet mass; the complement to 100 % of the moisture content. → chapter 1.2

Edge coating (enduit de bord)

Coating (latex, synthetic rubber) applied to the edges of a non-gasketed cloth to limit weeping by capillary action and to protect the edge. → chapter 4.3

Eyelet (œillet)

Ring crimped into the edge of the cloth, by which it is attached to the plate (lugs, ties) [3]. → chapter 3.4

Feed neck (col d'alimentation, manchon)

Tubular part of the cloth that passes through the plate's feed eye and joins its two faces; sewn, welded, moulded or coated depending on the design. → chapter 3.4

Filter cake (gâteau)

Solid residue that forms on the medium during filtration [1]; it is discharged when the filter opens. → chapter 1.2

Filter press (filtre-presse)

Batch filter made up of a series of plates covered with filter medium, between which the filter cakes form [1]. → chapter 2.1

Filtrate (filtrat)

Liquid that has passed through the filter medium [1]. → chapter 1.1

Filtration cycle (cycle de filtration)

Complete sequence of a batch filter: closing, filling, filtration, possibly squeezing, washing and air blowing, then opening and cake discharge. → chapter 1.3

Filtration fineness (finesse de filtration)

Size of the smallest particles a medium retains under given conditions; for a filter press cloth, it depends mainly on the product and on how the filter cake forms. → chapter 3.3

Flocculant (floculant)

Reagent added to the slurry to agglomerate very fine or colloidal particles into larger flocs [1] that are easier to filter; overdosing can foul the cloths. → chapter 4.4

Hanging bar (barre de suspension)

Bar from which the cloth is hung above the plate, a common system on large filters in the mining industry [3]. → chapter 3.4

Hook-and-loop strip (bande auto-agrippante)

Hook-and-loop fastening that closes the cloth around the plate by overlapping; it avoids plastic parts that might fall into the product [3]. → chapter 3.4

Hydrolysis (hydrolyse)

Degradation of a fibre through prolonged exposure to hot water or steam; the weak point of polyester [4]. → chapter 3.1

Initial turbidity (trouble initial)

Phase at the start of the cycle when the filtrate is still cloudy, because no filter cake has yet formed [1]. → chapter 3.3

ISO 9237

International standard for measuring the air permeability of fabrics; standard test area of 20 cm², 200 Pa for industrial textiles, result in mm/s [2]. → chapter 3.3

Mass per unit area (masse surfacique)

Mass of a fabric per unit area, in g/m²; a heavier cloth is not necessarily more durable. → chapter 3.3

Medium resistance (résistance du média)

Share of the resistance to flow due to the filter medium itself, distinct from that of the filter cake. → chapter 1.3

Membrane plate (plateau à membrane)

Plate with a flexible face which, inflated with water or air at the end of filling, squeezes the filter cake to drive out liquid. → chapter 2.2

Monofilament (monofilament)

Yarn made of a single extruded strand, smooth and strong: excellent cake discharge, lower retention of fines. → chapter 3.2

Multifilament (multifilament)

Yarn made of many very fine continuous filaments twisted together: average retention and cake discharge. → chapter 3.2

Needle felt (feutre aiguilleté)

Nonwoven medium made of randomly oriented fibres bonded mechanically by needling. → chapter 3.2

Nominal rating (rétention nominale)

Approximate retention capability, highly dependent on the test protocol; a comparison indicator, not a guaranteed cut-off [1]. → chapter 3.3

Open area (surface ouverte)

Proportion of a medium's surface that is open to flow, as a percentage [1]. → chapter 3.2

Plain weave (toile, armure unie)

The simplest weave, each yarn passing alternately over and under: tight, stable fabric, good retention. → chapter 3.2

Plate core (âme du plateau)

Central part of a filter press plate, around the feed eye; its thickness is one of the dimensions to supply when ordering a cloth. → chapter 3.4

Plate pack (pack)

The full set of plates in a filter press, clamped between the head and the moving end plate; cloths are identified by their position in the pack. → chapter 4.1

Polyamide, PA (polyamide)

Synthetic fibre usable at around 100 to 110 °C continuously [4]; tolerates bases but not strong mineral acids. → chapter 3.1

Polyester, PES (polyester)

Synthetic fibre usable at around 130 to 135 °C continuously, sensitive to hydrolysis [4]; not recommended with bases. → chapter 3.1

Polypropylene, PP (polypropylène)

The most common fibre for filter press cloths, limited to around 80 to 90 °C continuously [4]; good resistance to common mineral acids and to caustic soda. → chapter 3.1

Pressure drop (perte de charge)

Pressure difference between two points in a flow [1], for example on either side of a cloth or a filter cake. → chapter 1.3

Retention (rétention)

Ability of a medium to stop particles; it cannot be inferred from air permeability. → chapter 3.3

Satin (satin)

Weave with long yarn floats on the surface, giving a very smooth face that favours cake discharge. → chapter 3.2

Sealing edge (bord d'étanchéité)

Peripheral surface of the plate on which two adjacent plates close, gripping the cloth; filter cake left on it causes leaks. → chapter 4.3

Selvedge (lisière)

Woven, uncut edge of a fabric; its yarns are held in place and it resists fraying [1]. → chapter 3.4

Slurry (suspension)

Mixture of liquid and solid particles sent to the filter; also called the feed. → chapter 1.1

Spun yarn (fil filé, fibres coupées)

Yarn made of short fibres combed then twisted: excellent retention, poor cake discharge. → chapter 3.2

Twill (sergé)

Weave whose offset interlacings form diagonal lines; a more supple fabric, a common compromise. → chapter 3.2

Warp and weft (chaîne et trame)

The two yarn directions of a woven fabric: the warp along the length of the loom, the weft perpendicular to it. Breaking strengths are given in both directions. → chapter 3.2

Weave (armure)

The way the warp and weft yarns interlace in a fabric: plain, twill, satin. It affects retention, cake discharge and blinding [3]. → chapter 3.2