Document o9yGbNJeNzoLgbkD21oG58jXg

American Society of Heating and Ventilating Engineers Guide, 1930 where it would not be sufficient to carry the material from the machines still in operation, and thus result in clogging the pipes; Accordingly, it is sometimes desirable to use velocities higher than the minimum to allow a factor of safety to cover this contingency. In some states codes have been issued specifying suctions to be main tained for the more common dusts. A suction standard should always be considered in conjunction with the shape of hood, and size connection, as these factors together determine Table 1. Size of Connections for Wood-Working Machinery Type of Machine Diameter of ' Connections in Inches Circular Saws, 12-in. diam Circular Saws, 12-24-in. diam............... ....................... ... Circular Saws, 24-40-in. diam......... ,,........ ..................... Band Saws, Blade under 2 in., wide............................... Band Saws, Blade 2-3 in. wide______________________ Band Saws, Blade 3-4 in. wide--.................................... Band Saws, Blade 4-5 in. wide--................ ............... ... Band Saws, Blade 5-6 in. wide.,___________ _________ _ Small Mortisers................ .................................... ............. Single End Tenoncrs............................... ......... ......... ..... Double End Tenoners...................................................... Double End, Double Head Tenoners............................ Planers, Matchers, Moulders, Stickers, Jointers, etc. With Knives, 6-10 in......... ......................... ............ With Knives, 10-20 in................ ........................... . With Knives, 20-30 in............. ................................. Shapers, Light Work........ ................................................ . Shapers, Heavy Work............ ......................... ......... ....... Belt Sander, Belt less than 6 in. wide--........................ Belt Sander, Belt 6-10 in. wide..................................... Belt Sander, Belt 10-14 in. wide--_______ ______ ___ Drum Sander, 24 in................ .......................... ;;____ ___ Drum Sander, 30 in,.......................................................... Drum Sander, 36 in.............................. ............................. Drum Sander, 48 in.._...................... ................................ Drum Sander, over 48 in.......................... --................... Disc Sander, 24 in. diam........................................ ......... Disc Sander, 26-36 in. diam......... ................................. . Disc Sander, 36-48 in. diam--...... ................................. Arm Sander.......................................................................... 4. 5 6 4 5 6 7 8 6 6 7 10 5-6 6-8 6-10 4-=5 8 5 6 7 5' 6 7 8 10 5 6 7 4 the volume of air exhausted and its velocity, which in turn are a measure of the effectiveness of the exhaust system. The volume of air of standard density taken into the system-at each connection is given by the formula: where <2 = 4,0004(1) Q = cubic feet of air per minute. A = area of connection in square feet. / = orifice or restriction coefficient. * = static suction measured in inches of water. 460 Chapter 28--Pneumatic Exhaust Systems Table 2. Size of Connections for Grinding and Buffing Wheels Diameter of .Wheels Grinding-- 6 in. or less, not over 1 in. thick.------- ______ 7 in. to 9 in., inclusive, not over 1 10 in. to 16 in., " " "2 in. in. thiUck...... 17 in. to 19 in., " " " 3 in. 20 in. to 24 in., 25 in. to 30 in., " " " " "4 "5 in. in. U __ Max. Grinding Surface Sq. In. 19 43 101 180 302 472 Min. Diam. of Branch Pipes in Inches 3 3H 4 4H 5 6 Buffing-- 6 in. or less, not over 1 in. thick. ... - 7 13 in. in. to to 12 16 in., in., inclusive, " not " over 1J^ in. " 2 in. thaick___ 17 in. to 20 in., " " 3 in. 21 in. to 27 in., " " " 4 in. 27 in. to 33 in., " " " 5 in. 19 57 101 189 338 518 3H 4 4H 5 6 7 The orifice coefficient / is dependent upon the shape and construction of the hood and will range from 60 to 90 per cent. An average value is 70 per cent. Knowing the suction at each hood and the diameter of each connection, the volume of air passing up each branch can be. taken from Table 4. The sum of all these volumes gives the total volume to be handled by the exhaust fan. Common practice is to provide a main suction pipe having an area 20 to 25 per cent in excess of the sum of the areas of the branches entering it between the point in question and the dead end of the main. Similarly the discharge pipe leading from the fan outlet to the collector is frequently made the same diameter as the large end of the main suction pipe. The reason for this increase in size is that a considerable power saving results from the lower air velocity. However, there is no technical reason why Table 3. Suction Pressures Required at Hoods for Connections of Usual Proportions - Static Suction m Inches op Water 2 2 2 2-4 2-3 2 2 2 2-4" 2-3 2-3 2 3-5 461