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Filtration Glossary continued n-r

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Filtration Glossary continued n-r

Machine Coolant Filtration Glossary

Here is a glossary of Filtration Terms and their meanings.  Please refer to the Machine Coolant Filtration Index for articles and information on these topics.  

A - C  |  D - F |  G - M  |  N  |  O  |  P  |  Q  |  R  |  S - Z


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. 

Needle Punched:  A term for nonwoven materials that have been processed with reciprocating banks of needles.  The needles have barbed ends that drag fibers in a direction perpendicular to the normal orientation of the fibermat.  Needling greatly improves the dimensional stability and tensile strength of nonwoven fibrous webs.  Felt is a material commonly formed using needling. 

Negative Pressure:  Pressure less than atmospheric pressure; Vacuum or suction. 

Nephelometer,  An instrument that measures the intensity of light transmitted or scattered by a sample of fluid.  Particles present in the fluid cause light to be scattered.  Nephelometers measure gross or multiple particle scattering.  Turbidimeters are nephelometers.  Sensors used for DOP measurements are frequently nephelometers.  See turbidity, NTU. 

Nominal:   An arbitrary term used to describe or define a degree of filtration.  The filtration industry used various methods of determining nominal ratings which are not necessarily interchangeable.  Generally nominal references 98% removal of solids above a specified micron rating on a single pass basis.  See absolute. 

Nominal Rating:  A rating used by some filter manufacturers to describe the particle removal characteristics of their product.  An example of such a rating would be a product labeled as “5 micron nominal”.  Such ratings are largely meaningless and usually confusing.  Nominal ratings are sometimes used for filters that do not have district particle cut off characteristics.  See absolute rating, beta ratio, filtration ratio. 

Non-Aqueous: not water borne, water related, water resembling, or containing water. 

Non-Polar:  A compound or element whose electron capacity is satisfied.  A neutral condition that will remain unreactive.   Not polar. 

Non-Toxic:  Having a non-poisonous effect. 

Nozzles:  Connections at the inlet and outlet of a vessel through which product flows; or connections in a vessel which permit connecting of accessories, etc. 

NPT:  National pipe thread standard. 

NTP:  Normal conditions of temperature and pressure.  Whenever this term is used, it refers to a gas measured at a pressure one (1) atmosphere absolute (760 mm. Of Hg.) and a temperature of 00C.  However, some sources use a different reference temperature to define NTP. 



Occluded:  Taken in and retained, absorbed. 

O.D.:  Outside diameter. 

Opening:  Term covering several processes in the preliminary treatment of raw cotton, the primary objects are to separate the compressed and matted masses of cotton into loose tufts and to remove the heavier and bulkier Impurities.  Also Used To Describe Pore Size. 

Operating Pressure:  The normal ones sure at which a system operates.

Operating pressure, critical:  Pressure above-the normal or design limits which may cause damage or rupture. 

Operating Pressure, Maximum:  The maximum pressure allowed in the system. 

Organic:  Describes the vast number of chemical substances containing carbon, hydrogen, and oxygen. 

Organic Solvents:  Substances in which an organic material will dissolve. 

Outer Shell:  Outer covering of an element usually perforated or screen. 

Outer Wrap:  Outside covering of an element. 

Outside-In:  Flow of product from outside to inside of element. 

Oxide:  Combination of oxygen with another element. 

Oxidation:  A chemical combination of any substance in which the oxidation state (positive valence) of an element is increased. 



Paper:  Medium used in many elements.  A very general term applied to resin impregnated cellulose.  Many types of paper or cellulose are used as filter media made to specifications. 

Particle Count:  A practice of counting particles of solid matter in groups based on relative size.  Frequently used in engineering a filter to a specific task or to evaluate the performance of a filter under specific operating conditions.  When used as data to engineer a filter, proper consideration can be given the type of media to be used, expectant life of the media, and the true cost of operation. 

Particle Size Distribution:  A tabulation resulting from a particle count of solids grouped by specified micron sizes to determine the condition of either the influent or effluent stream.  Usually expressed in percentage of total solids to the specific group.  Example: 31% in the 6 to 10 micron group.  See particle count. 

Particulate:  Relating to minute, separate particles. 

Perforated:  Describes material in which holes have been punched, such as the materials of which the center tube of a cartridge is made. 

Permeability:  Ability of a cake or medium to pass liquids; or 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. 

Permeable:  Material that has openings through which liquids will pass in filtering.  Also referred to as porous or pervious. 

Pervious:  Material that has openings through which liquid will pass in filtering.  Also referred to as porous or permeable. 

pH RANGE:  An arbitrary scale of numbers from 0 to 14 indicating acidity or basicity of a solution.  A neutral solution has a pH of 7; below 7 represents acidity, and above 7 represents basicity.  See article on Testing Machine Coolant for ways to test pH levels. 

Phase:  May be continuous, as the basic product flowing through a vessel; or discontinuous, as the material to be removed from the basic product.  Both are distinct and separate. 

Phase Inversion:  Precipitation from a polymer phase from a solution.  This is the process commonly used to make microporous membranes. 

Phenolic Resins:  Synthetic thermosetting resins obtained by the condensation of phenol or substituted phenols with aldehydes.  Used as a binder in cellulose and glass fibers to form filter media. 

Pitot Tube: A device used to measure the velocity of gas in a duct. 

Plain Weave:  The simplest and most common weave, repeating pattern of two warps and two filling yarns.  Also known as “one up and one down” weave. 

Plastisol:  A suspension of the thermosetting plastic which can mold into any desired shape.  Used as a combination end cap and gasket on element. 

Plate and Frame Filter:  Type of pressure filter which consists of a series of plates matched with frames to sandwich media for flow in one side, through the media and out the other side. 

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

Plugging:  Where filtered out particles fill the openings in the 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 binding or blocking. 

Ply:  The number of individual yarns twisted together to make a composite yarn. 

Polar:  A compound of element capable of receiving or giving electrons.  See non-polar. 

Polish Filter:  A filter located downstream of roughing filters.  Polish filters remove the last traces of contaminants. 

Polycarbonate:  A clear, tough polymer with good temperature and chemical resistance.  Polycarbonate can be molded and is sometimes used for filter housings. 

Polymerization:  The union of monomers or molecules to form a polymer consisting of giant molecules.  Two to many thousand molecules may be required to form one polymer molecule. 

Polysulfone:  A polymer used in some reverse osmosis membranes.  Polysulfone has good resistance to chlorine, allowing polysulfone membranes to be cleaned with hypochlorite solutions. 

Polytetrafluoroethylene: The chemical name for Teflon.  Also called PTFE. 

Polyvinyl Chloride:  A polymer used in plastic pipe and some plastic filter housings.  Also called PVC. 

Polyvinylidene Diffluoride,  A polymer used in some membranes.  PVDF has good chemical and temperature resistance.  It is fairly inert. 

Pores:  The openings in a medium.  Also referred to interstices.  Sizes and shape of openings in cellulose are closely controlled in manufacture. 

Porosimeter,  An instrument used to measure pore size in filter materials. 

Porosity:  The ratio of void volume to total cake volume.  Also describes filter media which may have larger pores than any other cake media. 

Porous:  Material that has openings through which liquid will pass in filtering.  Also referred to as permeable or pervious. 

Positive Displacement Pump,  A pump that delivers constant flow regardless of large changes in the back pressure on the pump. 

Potable:  Drinking, (water). 

Pour Point:  The lowest temperature at which a liquid will pour or flow when chilled without disturbance under specified conditions. 

PPM,  See parts per million. 

Precoat,  A cake formed on a filter, usually using a slurry or filter aid.  Some filters such as plate and frame filters, pressure leaf filters or rotary drum filters require a precoat step before filtration of the liquid can proceed. 

Precoating:  The operation of deposing an inert material (filter aid) prior to beginning filtration. 

Prefilt:  Material to be filtered.  Also referred to as concentrate, feed, influent, intake, liquor, mud, pulp, slimes, or sludge. 

Prefilter:  Filter for removing gross contaminate before the product stream enters a separator/filter.  Used to remove gross solids. 

Prefilter/Coalescer:  Two-stage, horizontal vessel for efficient solids and water removal at high flow rates.  Used on light gravity streams. 

Prefilter/Coalescer/Separator:  Three stage vessel for use where stream carries an unusually high amount of solids, prefilter elements in first stage remove bulk of solids and permit coalescer and separator elements in next two stages to function more effectively for phase separation. 

Pressure, Absolute:  Gauge pressure plus 14.7 psi. 

Pressure, Atmospheric:  The force exerted by the atmosphere at sea level which is equivalent to 14.7 psi. 

Pressure, Expressed In Atmospheres:  The total gauge pressure divided by 14.7 and expressed in psi. 

Pressure, Partial:  In a mixture of gases, each gas exerts a pressure equal to the total pressure multiplied by the mole fraction (or volume fraction) of the individual gas.  The sum of the partial pressure equals the total pressure. 

Pressure, Proof:  A test pressure above normal operating pressure, to assure that part will withstand the norm, without damage or leakage. 

Pressure Differential:  The difference in pressure between two points. 

Pressure Drop:  The difference in pressure between two points, generally at the inlet and the outlet of a filter or a separator/filter.  Measured in pounds per square inch gauge, or in inches of mercury. 

Pressure Drop, Maximum Allowable:  The maximum pressure differential of a vessel under specified product and flow conditions. 

Pressure Relief:  Valve which permits enough liquid or gas to escape from the vessel to prevent extreme pressure buildup within a vessel. 

Product:  A general term used to describe the continuous phase, either liquid or air or gas, which is being processed through filtration or separation/filtration equipment.

Prover Tank:  Vessel for proving the volumetric accuracy of positive displacement meters.  Also called meter calibrating tank or meter proving tank. 

PSI:  Pounds per square inch. 

PSIA:  Pounds per square inch absolute. 

PSID:  Pounds per square inch differential. 

PSIG:  Pounds per square inch gauge. 

Pulsating Blowback:  Intermittent, on-off blowing, with or without cake discharge. 

Purification:  A general term describing the removal of water or hydrocarbon in vapor form from an air or gas steam.  Differs from entrainment removal in that the dew point of a gas stream will be lowered by vapor removal.  May be the same as dehydration, classification, or clarification. 



Quiescent:  State of the rest of a body.  In the case of entrainment separation, the body would be a liquid.  Also used to describe a sump containing evacuated liquids or solids. 



Rate Of Flow Control:  Valve operated by differential pressure across an orifice, for control of the rate at which a product flows through a vessel. 

Rated Flow:  Normal operating flow rate at which a product is passed through a vessel; flow rate which a vessel and media are designed to accommodate. 

Raw Sludge:  Untreated sewage sludge. 

Rayon:  A generic term for filaments made from various solutions of modified cellulose by forcing or drawing the solution through an orifice and solidifying it in the form of a filament or filaments by means of some coagulating or precipitating medium.  See acetate rayon. 

Rayon Yarn, Denier Of:  Numerically equal to the weight in grams of 9,000 meters of yarn. 

Rectangular Mesh:  Wire 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”. 

Recycle:  Return of filtered liquid for another filtering; a continuous flow of liquid through an open of closed system. 

Redistill:  Re-treat a distillate. 

Regenerated:  Cleaned of impurities and made reusable. 

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

Repack:  Cylindrical element used in single stage separator/filter for removal of one liquid and coarse solids from another liquid.  May be used as a single element, a combination of wafers, or a cluster type.  Medium may be excelsior, glass fibers, or steel wool; or a combination of glass fibers and metal mesh. 

Repellency:  Quality of repelling water, or being hydrophobic; opposite of water wettable. 

Replaceable:  Describes elements which are to be discussed after use and replaced with an identical element.  Same as disposable.  Opposite of reusable. 

Residue:  Solids deposited upon the filter medium during filtration in sufficient thickness to be removed in sheets or sizable pieces.  Sometimes referred to as cake or discharged solids. 

Resin Impregnated:  Treatment of cellulose used in paper elements.  Impregnation is carefully controlled in the manufacture of cellulose and provides a binder for the fibers which must be cured to specification during cartridge manufacture to preserve all the properties of the original specification for the cellulose. 

Retainer:  Any device which holds a component in place.  

Retrofit:  Another term used for the conversion of a filter or separator/filter. 

Reusable:  Describes element which may be cleaned and used again.  Opposite of disposable or replaceable. 

Reverse Osmosis,  A process that uses pressure to drive fluid through a semiperimeable membrane in the opposite direction normal osmosis would dictate.  During reverse osmosis the fluid will flow from the high ionic concentration side of a membrane.  This is a useful technique for desalination of water or concentration of waste streams that contain dissolved ionic species. 

Reynolds Number,  A number used to characterize important properties of flowing fluids.  The Reynolds number represents the ratio of internal forces.  The Reynolds number is frequently used to predict whether fluid flow under given conditions will be laminar or turbulent. 

Rheology,  The study of flow properties such as elasticity, plasticity, viscosity, dilatancy, and thixotropicity. 

Rotameter,  A commonly used flow meter which uses a suspended ball to measure flow rate. 

RTJ:  Ring type joint.  Describes a flange facing.  May be either slip on, weld neck, or long weld neck. 

Runs:  Cycles or batches.