Document O9xgpeJOMqd5bDE5Ybk11NQe

Digest of Industrial Hygiene - 9. 440 Practical Discusalonof Dust Units Baoloyed in Ventilation, FJ. Kravath. Saf Praotlcc Bull. No. 63,Penna. Dept/of Laborand Industry, May, 1941. This ertlals reviews general types of filters, their capabilities and fallings and their cooperative worth as shown by the experience record of installations in tho abrasive industry. Among those types discussed are the gravitational filter or settling tank, the cyclone, cloth filters, electrical precipitation air washers. The gravitational filter is recommended only as a preliminary cleaning device. Its velocities should be tcopt from 100 to 250 fjm. this typ of installation is practically wear and maintenance free, since the dust comes GLn in contact with practically none of the filter ports while it still has any (3) velocity. The cyclone unlike the gravitational filter increases in efficiency with the decrease in size of, at least, the dloaetor. Because of its high eft oiencles, it is probably the most widely used collector. These installations m find their greatest application where the dust or colloctod materiel is nonabrasive m action. Cloth filters are used primarily where high efficiencies are nooessery for the reclamation of valuable material, where recirculation is desired as a means of reducing heating losses, or in residential districts tdu it is unlawful to discharge visible solids into the atmosphere. The original cost is higher than for tho cyclone but its efficiency le unquestioned, Its 11 extremely long, and maintenance fairly simple. ZLeotrleal precipitation offej poshaps the most efficient type of separation but its Initial cost le high. Therefore, its application will probably be restricted to .the reclamation of valuable or extremely dangerous materials. Efficiencies of air washers are s< what lower than cloth filtors, but occasionally lack of proper application en< maintenance of the latter tend to make tho former, the more praotlcal unit* I' cost averages about one-third that of the doth filter dosign. 441 A Comparison of the Weight. Particle Count end Discoloration Methods of Teatli Air filters. g.3. Bowler and R.C. Jordan. Heating. Piping. Air Pond.. 13. 246-35 (April, 1941). The relative merits.of throe filter tost methods based on weight, particle ear and discoloration are analyzed and the results of nmerous tests are correlat with the theory of filtering air. In the testa by the counting method, the authors employed both an adhesive impingement type of dust counter and settll chambers. Balatlvaly low dost concentrations were necessarily used in testa these instruments. There is considerable evidence that arrestances based on tide count aro thobeat measures of tho degree to which dangerous dust is el inatod, . but ere not necessarily measures at degree at rtsoval at nuisance dua Moroover in its present state of perfection, this method requires too long a time to make a statistically reliable determination. The weight method has t advantage of high accuracy, and readily allows determinations at filter life dost bolding capacity as wall os arrestanoe. However* the role of the lnxgos dust particles is exaggerated and the method gives little lnfoxmatlaa on exit tencas due to smaller particles. Both tho transmitted and reflected light di coloration methods have a reasonably good accuracy (3$), and the reflection method is probably the best for moasuring reduction of soiling power. In tbs reflection method the blank is fairly constant, while it varies considerably the transnlsalon oetbod. Both methods measure tho reduction and discolomtit only in relation to the test dust being used, and the orrestances vary groat] for the same filters with different dusts. The photo-electric cell method* 1 is tho best measure of the reduction in discoloration* while the crucible ns* is the best measure of the reduction of the larger visible dust particles* question of which is the best Indicator of removal of nuisance dust is left <