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670 CHAPTER 31 1952 Guide Air Duct Design 671 CU FT OF AIR PER MINUTE CU FT OF AIR PER MINUTE' For Volumes of 10 to 2000 cfm (Based on Standard Air of 0.075 lb per eu ft density flowing through average, dean, round, galvanised metal ducts having approximately 40 joints per 100 ft.) No safety factor included. Caution: Bo not extrapolate below chart. Vor Volumes of 1000 to 100,000 cfm (Based on Standard Air of 0.075 lb per cu ft density flowing through average, clean, round, galvanised metal ducts having approximately 40 joints per 100 ft.) No safety factor Included. Figs. 1 and 2, covering volume ranges of 10 to 2000 cfm, and 1000 to 100,000 cfm, respectively. These charts were developed by the A.S.H.V.E. Re search Laboratory.1 They do not include any safety factor. The charts, Figs. 1 and 2, were constructed from the basic flow equation for the pressure loss in circular ducts (see Chapter 4):