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706 CHAPTER 33 1950 Guide force upon specially shaped blades of an exhauster wheel,' and then conveyed through a dust circuit in the fan casing to the dust storage hopper. 4. Cinder Catching Fan: This is a. Special type of collector in which removal of solids is effected by a slotted scroll. It is a fan unit which is often used for the'dual purpose of dust removal and induced draft service. SETTLING CHAMBERS : While it would be possible in theory to remove dust by settling in a large chamber when conveying velocities are reduced to the point where the particles would no longer be held in suspension, such devices have little practical application in dust collecting equipment. Extreme space require ments and the presence of eddy currents may nullify the effective veloc ity. The settling chamber type of collector, can therefore be used only for removal of extremely coarse particles. Pressure drop, should be J to j in. water column, plus that necessary to accelerate the air motion to the re quired conveying velocity at discharge of the settling chamber. - TESTING METHODS Methods of determining the performance.of industrial air cleaning de vices will depend upon the nature of the air contaminant, its quantity, the required accuracy of the test, and the type of air cleaning device. The technics used'in collectmg the samples are the same as those utilized in the field of industrial hygiene. The tests may be facilitated by feeding uniformly a known amount of the material to be removed. The performance efficiency may be calculated from the amount of material introduced, the quantities of air involved, the amount of material intercepted and the quantity that escapes. When it is necessary to test the device under actual use,' the material entering and-! leaving must be sampled simultaneously over a sufficiently long period of time to collect an adequate amount for analysis. If feasible, the quantity, of material removed by the cleaning device during the test period should also be determined. Unusual care must be exercised in collecting the samples to insure that the sampling areas selected are actually representative of the material enter ing and leaving the cleaning device, With gases, vapors and fresh fumes, this problem is not great. On the other hand, mists, dusts and aged fumes may present considerable trouble. When the materialis confined in a duct system, it is common practice to collect the sample along the center line. The sampling tube is located.parallel with and facing the flow. .The sampling velocity should be approximately the same as the air velocity in the duct. With large ducts it may be desirable to make traverse tests to locate an optimum sampling position. REFERENCES `Bronchial Asthma and Allied Allergic Disorders, by S. S. Leopold and C. S. Leopold (Journal of the American Medical Association, March 7,1925, Vol. 84, p. 731-! 734). Dirt Patterns on Walls, by R. A. Nielsen (A.S.H.V.E. Transactions, Vol. 46, 1941, p.247). . Industrial Dust, by Philip Drinker and Theodore Hatch'(McGraw-Hill.Co.,'New York, N. Y,). , 4 A.S.H.V.E. Standard Code for Testing and Rating Air Cleaning Devices Used in General Ventilation Work .(A.S.H.V.E. Transactions, Vol. 39,1933, p. 225). - 4 A Test Method for Air Filters, by Richard S'. Diil (A.S.H.V.E. Transactions, Vol. 44,1938, p. 379). Air Cleaning. 707' BIBLIOGRAPHY vj Design and Application of Oil-Coated Air Filters, by H. C. Murphy (A.S.H.V.E. Transactions, Vol. .33, 1927, p. 73). '; . Operation and Maintenance of Air Filters, by W. G. Frank (Heating, Piping and Air Conditioning, May, 1931, p. 378)'. Size and Characteristics of Air-Borne Impurities, by W. G. Frank (Heating, Piping: and Air Conditioning, January, 1932, p. 35). Fundamental Principles in the Design of Dry Air, Filters, by Otto Wechsberg, (A.S.H.V.E. Journal Section, Heating, Piping and Air Conditioning, April', 1933, p." 217). The Economic Factors in Converting Recirculated' Air for Ventilation, by H. E.` Ziel and Henry Sleik fA.S.H.V.E. Journal SECri'oN,.Heating, Piping and Air. Condi tioning, July, 1943, p. 367). Operation, Maintenance of Cloth-Screened Dust Collectors, by W. F. Terry (Heat ing, Piping and Air Conditioning, May, p. 259, June, p. 304,1933). Testing and Rating of Air Cleaning Devices Used in General Ventilation Work, by Samuel R. Lewis (A.S.H.V.E. Transactions, Vol. 39,1933, p. 277). A.S.H.V.E. Research Report No. 1094--Air Filter Performance as Affected by Kind of Dust, Rate of Dust Feed, and Air Velocity Through Filter, by F. B. Rowley and R. C. Jordan (A.S.H.V.E. Transactions, Vol. 44,1938, p. 415). A.S.H.V.E. Research Report No. 1122--Air Filter Performance as Affected" by Low Rate of Dust Feed, Various Types of Carbon, and Dust Particle Size ana Density, by F. B. Rowley and R. C. Jordan (A.S.H.V.E. Transactions, Vol. 45,1939, p. 339). A.S.H.V.E. Research Report No. 1145--The Effect of Lint on Air Filter Perform ance, by F. B. Rowley and R. C. Jordan (A.S.H.V.E. Transactions, Vol. 46,1940, p. 25). A.S.H.V.E. Research Report No. 1169--Comparison of the Weight, Particle Count and Discoloration Methods of Testing Air Filters, by F. B. Rowley and R. C. Jordan (A.S.H.V.E. Transactions, Vol. 47, 1941, p. 29). A.S.H.V.E. Research Report No. 1187--Economical Air Velocities for Mechan ical Air Filtration, by F.- B. Rowley and R. C. Jordan (A.S.H.V.E. Transactions, Vol. 47,1941, p. 391). A.S.H.V.E. Research Report No. 1218--Overloading of Viscous Air Filters Dur ing Accelerated Tests, by F. B. Rowley and R. C. Jordan (A.S.H.V.E. Transactions, Vol. 48,1942, p. 437). The Dust-Free Space Surrounding Hot Bodies, by H. H. Watson (Transactions of the Faraday Society, Vol. 32,1936, Pt. 2, p. 1073). A New Electrostatic Precipitator, by G. W. Penney (Electrical Engineering, Jan uary, 1937, p. 159). Electrostatic Precipitation for Aircraft, by Howard E. Corbitt and Norman J. Clark (Aero Digest, December, 1940, p. 132). Cleaning of Air and Gas by Thermal Repulsion, by Samuel C. Blacktin (Journal Society of Chemical Industry, 58,1939, p. 334-8, 59,1940, p. 153-4). Pointers on Selecting Equipment for Industrial Gas Cleaning, by C. E. Miller (Chemical and Metallurgical Engineering, 45, March, 1938, p. 132-5). Electrical Precipitation, by W. A. Schmidt and E. Anderson (Electrical Engineer ing, 57, August, 1938, p. 332-338). Electrostatic Precipitation for Cleaning Industrial Gases, by H. W. Wagner (Fuel Economist, 10,1935, p. 895-9,942-5,971-3). Dust Precipitation, by M. Pauthenier and Mm. Moreau-Hanot (Electrician, 113, August 10, 1934, p. 187-9). Alternating Current Precipitators for Sanitary Air Analysis: II. Acid Formation in Electric Precipitators, by W. G. Hazard and Tomoyoshi Ishikawa (Journal of Industrial Hygiene, October, 1932, p. 367-70). Electrical Precipitation, by A. W. Simon and L. C. Kron (Electrical Engineering, 51, February, 1932, p. 93-5).