Document wDqa3ewj3GjM0NZmbewzVxYy6

1052 CHAPTER 46 1956 Guide Table 6. Approximate Conveying Velocities Material Conveyed Design Velocity FPM 2,000 3,000 3.500 3,500-4,500 4.500 and over 3- ;=*- He 0.9S VP Ce 0.72 PLAIN DUCT END FLANGED DUCT END ZH-- h- Hm * 2.3 VP DUCT; OP BETTER; . 1.78 VP ORIFICE 049 VP DUCT . Ce 0.5S ORIFICE PUJS FLANGED DUCT 0ANY SLOT TTPC5) '-Ce _____ He* r S x vp Ce c Q*4003ACeVvF He * 0.50 VP C = 0.82 DIRECT BRANCH He = 0.85 VP Ce s 0.78 STANDARD GRINDER HOOD " F ENTRY LOSS FACTOR VP VELOCITY PRESSURE W DUCT SP* STATIC PRESSURE AT THROAT, INS. WATER CAGE X-rtc \ TWC He* ENTRY LOSS, INS. WATER GAGE Q - AIR VOLUME, CFM - A * CROSS SECTION AT THROAT, SO FT. C* COEFFICIENT OF ENTRY ENTRY LOSS FOR COMPLICATED HOOO SHAPES L BREAK HOOD INTO SIMPLE COMPONENTS 2. CALCULATE He FOR EACH COMPONENT 3. ADD VALUES OF He HOOD ENTRY LOSS Ce0.82- 098 TAPERED HOODS FLANGED OR UNFLANGED; ROUND SQUARE OR RECTANGULAR. 8 IS THE MAJOR ANGLE ON REC TANGULAR-HOOOS- -CEO- ai> ---j2D UWf-*-- TAPER R, (REGAIN) L, (LOSS) ANGLE. FRACTION OF FRACTION OF DEGREES VP DIFFERENCE VP DIFFERENCE 3.S 5 10 IS 20 2S 30 OVER 30 0.78 0.72' O.S6 0.42 0.28 0.13 0.00 0.00 0.22 0.28 0.44 0- 58 0.72 0.67 . 1.00 1.00 OTCELERATIQN LOSS L REGAIN TAPER L, (LOSS) ANCLE, FRACTION OF DECREES VP DIFFERENCE S O.OS 10 0.08 IS 0.08 20 0.10 23 0.11 30 0.13 4S 0.20 60 as ACCELERATION LOSS 8.ANGLE LOSS FRACTION OF VP IN DECREES BRANCH BRANCH ENTRY LOSS -S EQUALLY SPACED BRACKETS AS SHOWN WEATHER HOOD LOSS Fig. 2. Exhaust System Design Data13 Tapered hood data from Reference 37 Weather hood data from Reference 38 Industrial Exhaust Systems 1053 EXHAUST SYSTEM CONSTRUCTION SPECIFICATIONS AND DESIGN DETAILS15 Correct design and competent installation of sheet steel ducts and hoods are necessary for the proper functioning of any exhaust system. The follow ing specifications are mainly those recommended in the manual Industrial Ventilation.15 ......... General Requirements All exhaust systems shall be constructed with the materials recommended here with and shall be installed in a permanent and workmanlike manner. The interior of all ducts shall be smooth and free from obstructions; with joints either welded, flanged, or soldered air-tight. Materials a. Ducts shall be constructed of black iron welded or of galvanized sheet steel riveted and soldered unless the presence of corrosive gases, vapors and mists makes use of such material impracticable. Galvanized construction is not recommended for temperatures exceeding 400 F. Welding of black iron of 18 gage and lighter is -not recommended for-field fabrication. b. For average exhaust systems on non-corrosive applications the metal thickness in the following table shall be supplied. Diameter of Straight Ducts (Inches) U. S. Standard Gauge fob Steel Duct Class I Class II .Class III 24 22 20 22 20 18 20 18 16 18 16 14 Class 1. Includes ducts non-abrasive applications such as for paint spray, wood working, pharmaceutical, and food products. Class II. Includes ducts for non-abrasive material in high concentration flow pressure pneumatic conveying); moderately abrasive material; and highly abrasive materials in light concentrations. Typical examples are chemicals and wood dust; exhaust of foundry shakeouts and sand handling systems, grain dusts; coal crushing and screening; exhaust of grit blast cabinets; and grinding, buffing and polishing. Class III. Includes ducts for conveying all highly abrasive materials in moderate to heavy concentrations and moderately abrasive materials in heavy Concentrations as in: low pressure conveying of tobacco; and exhaust systems from abrasive cleaning operations, rock and ore screening and crushing, dryers and kilns, and flyash from boiler stacks. Where aluminum duct is indicated, the following equivalent B & S gage thickness of sheets should be used: Steel--U. S. Standard Gage Aluminum--B & S Gage . 26 24 22 20 18 24 22 20 18 16 c. Elbows and angles shall be a minimum of two gages heavier than straight lengths of equal diameter. d. Hoods shall be a minimum of two gages heavier than straight section of con1 necting branches. e. Where flexible piping is necessary, a non collapsible type of flexible piping shall be used and its length shall be kept at a minimum. / Construction a. Longitudinal joints of ducts shall be lapped, and riveted or spot-welded on 3-in. centers, maximum. b. Girth joints of ducts unless flanged or butt welded shall be made with lap in direction of air flow with not less than 1-in. lap.