Dialysis filter

84.21 - Centrifuges, including centrifugal dryers; fdtering or purifj4ng machinery and apparatus for liquids or gases. - Centrifuges, including centrifbgal dryers : 842 1.11 - - Cream separators 842 1.12 - - Clothes-dryers 8421.19 - - Other - Filtering or purifying machinery and apparatus for liquids : 8421.21 - - For filtering or purifying water - - For filtering or purifying beverages other than water 8421.23 - - Oil or petrol-filters for internal combustion engines 8421.29 - - Other 842 1.22 - Filtering or purifying machinery and apparatus for gases : - - Intake air filters for internal combustion engines 8421.39 - - Other 8421.31 - Parts : - - Of centrifuges, including centrifugal dryers 8421.99 - - Other 842 1.91 This heading covers : (I) Machines which, by the use of centrifugal force, completely or partly separate substances according to their different specific gravities, or which remove the moisture from wet substances. (11) Filtering or urifying machinery and apparatus for liquids or ases, other than, e.g., filter R funnels, mil strainers, strainers for filtering paints (generally hapter 73). (I) CENTRIFUGES, INCLUDING CENTRIFUGAL DRYERS r Most of these machines consist essential1 of a perforated plate, drum, basket or bowl, etc., revolvin at great speed in a stationary col ector, usually cylindrical, against the walls of which the expe led rnatenals are projected by centrifugal force. In some types the substances of different specific gravities are collected at different levels by means of a series of inverted es the solid ingredients are retained in the perforated revolving separator cones. In other drum,basket, etc., and the iquid ingredients expelled. Machines of this latter type may also be used to force liquids to penetrate thoroughly into materials (e.g., in dyeing or cleaning). 'P The heading includes : (1) Centrifugal driers for laundries, dyeworks, pulp mills, flour mills, etc. (2) Sugar refining centrifuges. (3) Cream separators and centrihgal clarifiers for milk. (4) Centrihges for clarifying oils, wines, spirits, etc. (5) Centrifuges for dehydrating or de-waxing petroleum products. (6) Centrifuges for dehydrating wines, tallow, starches, etc. (7) Nitrating centrifuges for gun-cotton manufacture. (8) Separators for yeast cultures. (9) Centrifhges for the chemical industry (e.g., high-speed extractors for antibiotics). (10) Centrifuges, mainly used in laboratories, in which liquids are separated in superimposed layers ready for decantation. (11) Centrifuges for separating the plasma from blood. (12) Centrifuges for drylng radioactive precipitates. (13) Centrifuges for extracting honey. PARTS anat^^ at^^ Sub'ect to the general provisions regarding the classification of parts (see the General Note to Sect~onXVI), parts of centrifuges are also classified here (e.g., plates, drums, bas ets, bowls and collectors). The heading excludes certain other types of machines operating on the centrifugal principle, e.g. : (a) Special centrifuges, called " gas " centrifuges, for the separation of uranium isotopes (heading 84.01). @) Centrifugal pumps for liquids (heading 84.13). (c) Centrifugal air pumps and blowers (heading 84.14). (d) Centrifbgal bolting (or sifting) machines for the milling industry (heading 84.37). (e) Centrifbgal casting machines for metal (e.g., for cast iron tubes) (heading 84.54), or for unhardened cements (e.g., for casting concrete tubes) (heading 84.74). (f) Centrihgal grinding machines (heading 84.74). (g) Centrifugal spin dryers for semiconductor wafer manufacturing (heading 84.86). (11) FILTERING OR PURIFYING MACHINERY AND APPARATUS, FOR LIQUIDS OR GASES Much of the filtration or purification lant of this headin is purely static equipment with no moving arts. The heading covers fi ters and purifiers o all types (physical or mechanical, chemicaf magnetic, elecho-ma etic, electrostatic, etc.). The heading covers not on1 large industrial plant, but also filters or internal combustion engines and small domestic app iances. The hea&ng does not, however, include filter funnels, milk strainers, vessels, tanks, etc., sim ly equipped with metallic gauze or other straining material, nor general urpose vessels, d s , etc., even if intended for use as filters after insertion of a layer of grave{ sand, charcoal, etc. 'i f ?' r In general, filterin machinery and plant of this heading is of two distinct types according to whether it is inten ed for liquids or gases. d (A) Filtering and purifying machinery, etc., for liquids, including water softeners. The liquid filters of this group separate solid, fatty, colloidal, etc., articles from a li uid, for example, by passing it through a sheet, membrane or mass o porous material ?e.&, cloth, felt, wire-cloth, skin, stoneware, porcelain, kieselguhr, sintered metallic owders, . In the treatment o drinking asbestos, paper pulp, cellulose, charcoal, animal black, remove bacteria, etc., in the water, some of these materials (e.g., porcelain and process of filtration; filters using these materials sometimes called " water purifiers ". Filters are also used to eliminate liquids from materials in the form of a slurry (e.g., from ceramic materials or ore concentrates). The heading covers liquid filters whether of the gravity, suction (or vacuum) or pressure types. P ? It includes, inter aIia : (1) Domestic type water filters. Pressure e domestic filters are designed for fitting to the mains pipes or to the tap, and usua ly consist of a cylindrical ceramic filtering element enclosed in a metal container. Gravi types are similar but often lar er. But the heading excludes filters made mainly o ceramics or glass (Chapter 6 or 70, respectively). B (2) Filter candles for man-made textile manufacture. These consist of a non-corrosive container housing a textile element which filters the spinning solution. (3) Oil filters for internal combustion engines, machine-tools, etc. They are of two main types : (i) Those containing a filtering element, usually of superimposed layers of felt, metallic gauze, steel wool, etc. (ii) Those containin permanent magnets or electromagnets for the extraction of ferrous particles from the oil. (4) Filters for boiler water. These usually consist of a large vessel fitted internall with several superimposed layers of filtering materials and, in addition to the inlet an outlet tubes, a system of pipes and valves for cleaning the filtering elements by a cross-current of water. (5) Filter presses. These consist of a horizontal series of filtering chambers formed by readily detachable vertical filter plates and frames; these are covered by a filtering medium (cloth, cellulose, etc.), and are held in place b a screw or press mechanism. The li uid is forced through the cells by a p m p , anithe chambers may be heated intern ly by steam, etc. The filtrate is drawn from the press and the residue collects in cakes between the plates. Filter presses are used for filtering or clarifying man liquids (e.g., in the chemical industry, the sugar industry, in brewing, wine A n g oil purification, ore concentration, in the manufacture of ceramics, man-made textiles, etc.). (6) Rotary drum vacuum fdters. These corn rise a c linder covered with filter cloth or gauze and mounted in the tank containing t e liqui to be filtered. The liquid is sucked into the drum,and mechanical devices remove the solid residue from the periphery. R dY (7) Intermittent vacuum filters. These consist of a number of" leaves " or chambers each covered with filter cloth and connected to a common vacuum line. The filter is submerged in the feed tank and the vacuum applied. (8) Chemical water purifiers, e.g., permutite or zeolite softeners and lime water purifiers. (9) Electro-ma netic water purifiers. In these purifiers the action of an alternating magnetic fie d prevents the calcareous salts in the water fiom crystallising and forming deposits on the walls of the tubes; instead, the salts separate as sludges which can readily be removed. q The headin also covers dial sers, s ecial type filters consisting essentially of a iquids can pass by diffision and thus be separated ' semi-permea le membrane thmugK which fiom colloidal particles. 7, I? (B) Filtering or purifying machinery, etc,, for gases These gas filters and purifiers are used to se arate solid or liquid particles from ases, either to recover products of value (e.g., coal ust, metallic articles, etc., recovere from furnace flue gases), or to eliminate harmful materials (e.g., ust extraction, removal of tar, etc., from gases or smoke fumes, removal of oil fiom steam engine vapours). i k 't' They include : (1) Filters and purifiers acting solely by mechanical or physical means; these are of two types. In the first t e, as in liquid filters, the s arating element consists of a porous surface or mass Felt, cloth, metallic sponge, g ass wool, etc.). In the second type, separation is achieved by suddenly reducing the speed of the particles drawn along wrth the gas, so that they can then be collected by gravity, trapped on an oiled surface, etc. Filters of these types often incorporate fans or water sprays. "P Filters of the first type include : (i) Intake air frlters for internal combustion engines. These often combine the two systems described above. (ii) Bag filters. These consist of a series of bag shaped cloth filtering elements, and often inco orate a shaker mechanism to cause the trapped particles to fall through the ottom of the bags. ? (iii) Screen filters. These consist of an endless filtering gauze running on two rollers and stretched across the chamber through which the gases are passed. The screen is cleaned by a scraper mechanism. (iv) Rotary drum filters, e.g., as used in sand blasting plant. They usually consist of a filter drum into which the air is drawn by suction. The drum revolves against a scraper which ffees the drum of the residue. Filters of the second type include : (v) Dust extractors, smoke filters, etc., fitted with various types of obstructing elements to reduce the speed of the particles in the gas stream, e.g., baffle plates, artitions erforated with non-correspondin orifices, circular or spiral circuits hted with affles, and cones of superimpose baffle rings. % (vi) Cyclones, usually consisting essentially of sheet metal cones enclosed in a cylindrical tank. The gases are fed into the narrower part of the cone by a tangential ipe and the turbulent currents thus set up decrease sharp1 as the gases approach t e broader section of the cone, so that the dust falls to the ottom of the tank E (2) Electrostatic filters for air or other gases in which the essential element is usually a series of vertical wires charged with static electricity. The dust in the air passin throu the apparatus is attracted to and retained on the wires from which it is remove perio ically, P (3) Gas scrubbers or absorption towers. These are used for purifying producer gas, coal gas, etc.; they consist of tall metal columns containing coke or other fillings, and fitted at the top with water sprays. (4) Other chemical filters and purifiers for air or other gases (including catalytic converters which change carbon monoxide in the exhaust gases of motor vehicles). This grou also includes the following machinery employed in the nu~learindustry : air filters specially esigned to eliminate radioactive dust (physical or electrostahc types); active-charcoal purifiers for retaining radioactive iodine; ion-exchange apparatus for the separation of radioactive elements, including such apparatus operating by electrodialysis; separators for irradiated fuels or for rocesslng effluents, whether operating by ion-exchange or operating chemically (by means o solvents, precipitation, etc.). i' PARTS Sub'ect to the general provisions re arding the classification of parts (see the General Exp anatory Note to Section XVI), the eadin covers parts for the above-mentioned types of filters and purifiers. Such parts include, inter o h : fl Leaves for intennittent vacuum filters; chassis, frames and plates for filter presses; rotary drums for liquid or gas filters; baffles and perforated plates, for gas filters. It should he noted, however, that filter blocks of pa er ul fall in heading 48.12 and that man other filtering elements (ceramics, textiles, felts, etc.) are c assi re according to their constituent material P FB The heading also excludes : (a) Gas difision apparatus for the separation of uranium isotopes (heading 84.01). (b) Air conditioning machines of heading 84.15 or air de-humidifiersof heading 84.79. (c) Wine-presses, cider-presses, etc. (heading 84.35). (d) Artificial kidney (dialysis) apparatus (heading 90.18). -