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Filtration Terminology

To intercept and retain, or drink in. To suck in, as a sponge sucks in water.

Activated Alumina
A highly porous and granular form of aluminium oxide having preferential adsorptive capacity for moisture from gases, vapours and some liquids. May be regenerated for extended use under specified conditions.

Activated Carbon
Any form of carbon characterised by high adsorptive capacity for gases, vapours or colloidal solids. The carbon or charcoal is produced by destructive distillation of wood, peat, lignite, nut, shells, bones, vegetable or other carbonaceous matter, but must be activated by high temperature steam or carbon dioxide which creates a porous particle structure.

The natural phenomenon of a gas, vapour or liquid being attracted to and held on the surface of a solid. To some extent adsorption takes place on any solid surface but certain materials have sufficient adsorbent capacity because of the finely divided material to make them useful in such industrial applications as the purification and separation of gases and liquids.

Ambient Surrounding. For example, the ambient operating temperature of a vessel is the temperature essentially the same as that surrounding the vessel.

American Society of Mechanical Engineers. Publish code which governs the design of pressure vessels.

Atmospheric Pressure
The presssure of approximately 14.7 pounds per square inch exerted at sea level in all directions by the atmosphere.

Wear caused by rubbing or friction. Produces fine particles that usually contaminate liquid that surrounds the point of attrition. Sometimes referred to as scouring or scoring.

A pressure vessel into which steam is introduced and held at a predetermined pressure and temperature for a period of time sufficient to ensure absolute sterility of implements and dressings associated with aseptic techniques practiced in all surgical operations and nursing care. Modern autoclaves are fully automatic and go through five separate stages during the sterilisation and drying of implements and/or dressings.

Where filtered-out particles fill the openings in the filter medium to the extent of shutting off the flow of product; loading up of the medium so as to reduce capacity. Also referred to as blocking or plugging.

Boyle's Law
If the temperature of a given kind of gas is held constant, the volume of a sample gas varies inversely with the pressure. See also Charles Law.

Charles' Law
If the pressure of a given kind of gas is held constant, its density is inversely proportional to its absolute temperature. See also Boyle's Law.

A mechanical device which unites discreet droplets of one phase of one phase prior to being separated from a second phase. Can be accomplished only when both phases are immiscible. Requires a tight media which is preferentially wettable and, by its nature of being tight, the filter is also a good filtering material. Good coalescing may only be accomplished by a coalescer cartridge when the specific gravities of the two phases are widely separate. As the gravities' difference becomes less, the two stage principle is generally required where finely coalesced discontinuous droplets are repelled by the second stage separator cartridges.

The process of cooling a vapour below its boiling point in order to liquify it.

The foreign matter in a fluid which has accumulated from various sources such as dirt, residue from wear of moving parts, atmospheric solids which can settle in a open system. Contaminates tend to discolour a liquid, cause additional wear on moving parts, cause system upsets in process streams or reduce the efficiency of a fluid. Water as well as a solid may be considered a contaminate when the presence of water causes adverse results. The presence of contaminates, whether liquid or solid, is the basis on which the use of filters or separator/filters is sought.

The conversion of metals into oxides, hydrated oxides, carbonates or other compounds due to the action of air or water, or both. Salts and sulphur are also important sources of corrosion. Removal of the solids and water reduces the effect or speed of corrosion in many cases.

Symbol designating pressure drop. The difference of pressure between two points, generally measured at the inlet and outlet of a filter, separator/filter etc. Normally measured in pounds per square inch (psi), inches of mercury (In.Hg.) or bar.

Compactness or thickness; ratio of weight of a medium to the weight of an equal volume of fibre. In general, mass per unit volume usually expressed in grams per cubic centimetre or pounds per cubic foot.

Depth Type Filtration
Filtration accomplished by flowing a fluid through a mass filter medium providing a tortuous path with many entrapments to stop the contaminates.

A drying agent or medium used in dehydration of air, gas and liquids. Examples silica gel, activated alumina, molecular sieve.

Temperature at which air is saturated with moisture, or in general the temperature at which a gas is saturated with respect to a considerable component.

Diffusion or Brownian Motion
A natural phenomenon. The random movement of very small particles (below 0.1 micron) caused by bombardment of those particles by gas molecules. As a result of this random or spiral movement, the particles describe paths much greater than their actual size and are, therefore easier to trap.

Direct Interception
The collection of relatively large particles (1.0 micron and over) on or near the surface of the filter medium. The particles collide with the fibres or structure of the filter medium, without deviating from streamline flow.

Dirt Holding Capacity
The volume of contaminate an element can hold before reaching the maximum allowable pressure drop.

D.O.P. Test
A cloud of mono-dispersed dioctylphtalate liquid droplets of 0.3 micron diameter is passed towards the filter under test. Efficiency is calculated by taking readings of upstream and downstream contamination levels with a particle counter.

Portion of the product stream which has already passed through the system or the portion of a system located after a filter, separator/filter etc.

Mist, fog or droplets transported by a fluid.

A term generally applied to a device used to remove solid contaminate from a liquid or as, or separate one liquid from another liquid or gas. A filter, as referred to in the industry, is limited to a device which removes solid contaminates only. If a device is used to remove solid and liquid contaminates, it is referred to in general terms as a separator, separator/filter or entrainment separator. A filter may be one of a number of such types as replaceable cartridge, cyclone edge, leaf, baffle, plate and frame, precoat, centrifuge. The term filter is sometimes erroneously used to describe the media used inside the vessel or filter case, but the correct use should be filter element, cartridge etc.

Flash Point
The lowest temperature at which a combustible liquid will give of a flammable vapour which will burn momentarily.

Term used in filtration and separation to include liquids, air or gas as a general term.

Glass Fibre
The proper reference to fibrous material made from glass that is commonly used as a filter and separator medium. Glass fibres may be used in blanket or tube form and, due to the random dispersal of the fibres, the material makes a good filter medium. Glass fibres are hydropholic (water wettable) and, as such, perform the function of coalescing immiscible liquids for separation. May be used effectively on compressed air, gas or liquids which are acidic or only slightly caustic.

Heat of Adsorption
The heat when a substance is adsorbed. It is the heat equivalent to the energy which the adsorbate must give up in going from its normal energy state to the lower energy state it has when adsorbed. The heat depends on the adsorbate and adsorbent.

Any one of a large number of compounds composed primarily of the elements carbon and hydrogen. As they increase in molecular weight and boiling point they may be respectively gases, liquids or solids.

Hydrostatic Test
A test conducted with either air, water or other fluids at a given value over design pressure, to prove the structural integrity of a pressure vessel.

Inactive-chemically inactive.

Inertial Impaction
The capture of particles (over 0.5 micron), within filter medium, as they fail to stay within the flow path of the fluid being filtered.

The spaces or openings in a medium. Also referred to as pores or voids. Usually refers to those voids contained in adsorptive medium such as carbon, fullers' earth etc. The available area for adsorbtion on or within a particle then must take into account not only the surface area but also that area within the particle due to the interstices, or voids.

Life Expectancy
The amount of use which may be expected from an element before it must be replaced; will vary according to the elements characteristics, the operating conditions, and the degree of contamination of the fluid being filtered.

A short unit of length in the metric system. One millionth of a metre, 10-4 centimetre, 10-3 millimetre or 0.000039 of one inch.

Visible water or hydrocarbon vapour, floating or falling in fine drops.

Molecular Sieve
Zeolite, natural or synthetic, or similar materials whose atoms are arranged in a crystal lattice in such a way that there are a large number of small cavities interconnected by smaller openings or pores of precisely uniform size. Used as drying agents for some liquids or gases as well as for some adsorbtive applications. May be regenerated for extended use under special conditions.

Molecular Weight
The sum of atomic weights of all atoms in a molecule. Sometimes referred to as the mole weight or mol weight.

Normal cubic metres per hour.

Describes a physical form of a cartridge made into a convoluted form to resemble the folds in an accordian.

Where filtered out particles fill the openings in the medium to the extent off shutting off the flow of product; the loading up of the medium so as to reduce capacity. Also referred to as blinding or blocking.

The openings in a medium. Also referred to as intertices.

The ratio of voids volume to total volume.

Filter for removing gross contamination before the liquid enters the main separator/filter.

Pressure, Absolute
Gauge pressure plus 14.7 psi (1 bar)

Pressure, Atmospheric
The force exerted by the atmosphere at sea level which is equivalent to 14.7 psi (1 bar).

Pounds per square inch.

Pounds per square inch absolute.

Pounds per square inch differential.

Pounds per square inch gauge.

Cleaned of impurities and made reusable.

Relative Humidity
The percentage relation that the actual amount of water vapour present in a given volume of air at a definite temperature bears to the maximum amount of water vapour that would be present if the air were saturated with water vapour at that temperature.

Standard cubic feet per minute.

Vessel which removes solids and entrained liquid from another liquid or gas. Uses a baffle and/or coalescer, or separator element. May be single stage, two stage or single or two stage with prefilter section for gross solids removal. Common application is the removal of water from gas. General reference to term implies the equipment is capable of both separation and filtration to specific degrees of efficiencies.

Sintered Medium
Filter medium manufactured by the fusion of powdered, granular materials. Sintering produces greater strength and density.

A mass or matter, contained in a fluid stream which is considered undesirable and should be removed; that part of the discontinuous phase which is removed from liquid or gas by filtration.

Sodium Flame Test
Developed by the Chemical Defence Establishment at Porton Down and adapted as a British standard for high efficiency filters-BS 3928 or BS4400. A dry salt particle cloud, 0.02 micron to 2.0 micron, is introduced into the air stream passing toward the filter under test. A sample of the filtered air is passed through a hydrogen flame which changes colour should salt particles be present. The change in colour of the flame is detected by a sensitive photo-multiplier which transmits a signal to micro-ammeter. Prior calibration of the micro-ammeter with known concentrations of sodium chloride in the hydrogen flame, enables very rapid tests to be carried out on high efficiency filters.

Specific Gravity
The ratio of weight of any volume of a substance to the weight of an equal volume of another substance. (Water for solids and liquids, and air or hydrogen for gases).

A laboratory instrument which measures the wave length and intensity of a light emitted by most chemical elements.

Stoke's Law
A physical law which approximates the velocity of a particle falling under the action of gravity through a fluid. The particle will accelerate until the frictional drag of the fluid just balances the gravitational acceleration, after which it will continue to fall at a constant velocity known as the terminal or free-settling velocity.

No viable or living organisms present.

Temperature, Absolute
Temperature measures from absolute zero which is minus 273°C, or minus 460°F.

Harmful, poisonous, injurious to life.

A semi permeable membrane capable of the separation of colloidal solids from liquids. Used in the process of reverse osmosis.

A substance in the gaseous form which under normal conditions of pressure and temperature would be liquid or solid.

A liquid has a viscosity of one poise if a force one dyne per square centimetre causes two parallel liquid surfaces one square centimetre in area and one centimetre apart to move past one another at a rate of one centimetre per second. There are a great many crude and empirical methods for measuring viscosity which generally involve measurement of the time of the flow or movement of a ball, ring, or other object in a specially shaped or sized apparatus.

The openings in the medium. Also referred to as interstices or pores.
Volumetric Flow Rate
Fluid flow expressed as a volume flowing per unit of time-cubic feet/min. or cubic metres/hr.

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