Document gD5LdQ1X84JkwwqK7mZ9YyOvV

838 CHAPTER 46 , , ' 1946 Guide Table 1. Rates of Flow Through Branch Pipes Woodworking Machines Pipe Diameter, In. 3 4 5 Air Volume, Cfm 200 350 550 Pipe Diameter, In. 6 7 8. Air Volume, Cfm 800 1100 1400 ' Tablb 2. Branch. Pipe Size for Woodworking Machine Hoods -Type op Machine Self feed table saw Other single saws Saws with Dado Head Band saws Disc sanders Triple drum sanders Size. In. . Min. Max. No. op Branches Minimum Diameter. In. . Bottom Branch Top Branch Others 25 4 18 1 ' 18 1 4 5 15 22 4 4 2 32 5 4 3 6 2 ; 5' 5 18 26 32 38 . 18 28 32 38 48 . 1 .1 2 2 3 4. 5 .4 5 . 5. 4 4 4 4 30 1 . 30 36 1 . 36 42 1 42 48 1 7' 8 9 10 Single drum sanders: (area in sq in.) Horizontal belt sanders Vertical belt sanders Jointers Single planers ' Tenoner 350 700 1400 9 6 9 8' 20 26 350 700 1400 2800 9 14 ' .6 9 14. 8 20 20 26 36 1 . 4a 5 6 7: 2 2 . . 5 6 14 15 .1 6 1, .1 1 1 1 4 5 5. 6 7' 2. ; 5 4 4 5 aNot over' 10 in. diameter. Table 3. Rates of Flow Through Branch Pipes Grinding and Buffing Wheels Pips Diameter, In. .3 . 4,- - -. 5 Ant Volume, Cpm 225 400 600 .. Pipe Diameter, In.' 6' 7' Air Volume, Cfm 900 1200 " ' Exhausting and Conveying Systems 839 Table 4. Branch Pipe Sizes for Grinding and Buffing Hoods ----- -------------_ Type of Wheel . Wheel Size Diameter, In. Maximum Branch Pipe Minimum Diameter. Min. Max. Width In. Area Sq In. Grinding 9 9 18 18 24 24 30 30 36 1 30 3 175 4 300 5 500 6 700 3 4 5 6 7 Disc Grinding 20 20 30 300 4 .5 . Buffing, Polishing and Scratch Brushing 8 2 50 8 16 3 150 16 24 . 4 300 24 30 ' 6 600 3X 4 56 respect to the hood are known. This is clearly indicated by Equation 3 which shows that the velocity at any point along the axis varies approxi mately inversely as the square of the distance. This formula coupled with Equation 1 should serve to indicate the velocity conditions to be expected when operations are conducted externally to the hood opening. Design Based on Total Air Flow Where the foregoing factors are not known, the usual method of designing an exhaust system is to base theair flow through the system on rates of flow through: each hood which have been found by experience to provide adequate control. For woodworking systems the rates of flow given in Table 1, calculated on the basis of a branch velocity of 4000 fpm, are adequate for control. Using these air flow rates, Table 2 gives the size of pipe connections to be used with the more common wood working machines. Properly designed grinding and buffing wheel hoods have been found to be adequately controlled when the rates of air flow, given in Table 3, calculated on the basis of a branch velocity of 4500 fpm, are used. Table 4 gives, the minimum branch pipe sizes to be used on the more common sizes of grinding and buffing wheels. In some states grinding, polishing and buffing wheels are- subject to. regulation by .codes. (See Standards, Chapter 51.), The static suction requirements, which range from 1J4 to 5 in. water displacement in a [/-tube, must be followed in such states although in several instances they appear to be excessive. Frequently, in these operations, a large part of the wheel must be exposed and the dust-laden air within the hood, is thrown outward by the centrifugal action of the wheel, thus counter acting useful inward draft. This tendency may be diminished by locating the connecting duct so as to create an air flow of not less than 200 fpm past the lower edge of the-wheel. : Controlling Air Velocities Exact determinations of hood control velocities are not available, but it is safe to assume that for most dusty operations velocities should not be less than 200 fpm at the noint of origin. . Recommended air velocities through hood openings for various processes are given in Table-5. For granite dust generated by pneumatic devices, velocities from 150 tq