Document VG8wMwZ9ov4gKvR3em1DKp67N

992 CHAPTER 46 . , 1953.Guide Table.6. Approximate Conveying- Velocities . Material Conveyed Fine dry dusts..................................................................... ............ Average industrial dusts...............................................................;. Coarse particles.................................................................................. Large particles, heavy' loads, moist materials............................... Design Velocity FPM 2,rinn . 3.500 3,500-4,500 4.500 and over He a 93 yp Ce - 0.72 PLAIN DUCT END r 1- He -049 VP Ceae2 FLANGED DUCT END CZ3- He> 1.76 VP Ce 0.60 SHARP-EDGED ORIFICE He 2.3 VP DUCT, OR BETTER. i.7B vp ounce 049 VP DUCT C 0.53 ounce plus FLANGED DUCT 04ANV SLOT TYPES) He* F X VP Q-4005ACVvp' IN Hq 030 vp Ce a 0.62 DIRECT BRANCH BOOTH He a 0.63 VP . Ce = 0.76 STANDARD GRINDER HOOP F ENTRY LOSS FACTOR VP - VELOCITY PRESSURE M DUCT SP- STATIC PRESSURE AT THROAT, INS. WATER GAGE Hg* ENTRY LOSS, MS. WATER GAGE Q* AW VOLUME,CFM A .CROSS SECTION AT THROAT, SQ. FT. Ce-COEFFICIENT OF ENTRY . ENTRY LOSS FOR COMFUCATED HOOO SHAPES L BREAK HOOO INTO SIMPLE COMPONENTS 2. CALCULATE Hq FOR EACH COMPONENT 3. ADD VALUES OF Hq HOOD ENTRY LOSS Ce*0.62- 096 TAPERED HOOPS FLANGED OR UNFLANGEDi ROUND SQUARE OR REC TANGULAR. 6 IS THE MAJOR ANGLE ON REC TANGULAR HOODS. -CCD- oi> --*j2D MHtj-*-- TAPER R, (REGAIN) L, (LOSS) AMGLE- FRACTION OF FRACTION OF . OCGREES VP DIFFERENCE VP DIFFERENCE 3.5 0.76 0.22 S 0.72 0.26 O.S6 0.44 a 0.42 1 0.36 20 0.26 0.72 23 30 oven so 0.13 0.00 0.00 0.67 1.00 ' 1.00 DECELERATION LOSS A REGAIN TAPER L, (LOSS) ANGLE, FRACnON -OFr DEGREES VP DIFFERENCE S 10 IS 20 25 30 . 45 60 0.03 0.06 0.06 0.10 0.11 0.13 T ' 0.20 - V as ACCELERATION LOSS ANGLE LOSS FRACTION . 6/ * OF VP IN DEGREES BRANCH iin. BRANCH ENTRY LOSS -SLEEVE WEATHER HOOD LOSS = Fig. 2. Exhaust System! Design Datau Tapered hood data from' Reference 37 ' . ^Weather hood data from Reference 38 . Industrial'Exhaust Systems 993 EXHAUST SYSTEM CONSTRUCTION SPECIFICATIONS AND DESIGN DETAILS15 Correct design and competent installation of sheet steel ducts, apd hoods are necessary for the proper functioning of any exhaust system. The follow ing specifications are mainly those recommended in the manual Industrial Ventilation.13 General Requirements All exhaust systems shall be constructed with the materials recommended here with and shall be installed in a permanent and workmanlike, mariner. The interior of all ducts shall be smooth and free frdin obstructions; with joints either welded, flanged, or soldered air-tight. ' Materials a. Ducts shall be construetedof 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 op Straight Ducts (Inches) Up to 8...................... ..................................... Over 8 to 18.......................................................................................... Over 18 to 30..................................................... Over 30............................................................... U. S. Standard Gauge por Steel Duct Class I 24 22 20 18 Class II 22 20 18 16 Class HI 20 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 (low 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 24 22 22 20 20 18 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 con 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 directions of air flow with not less than 1-in: lap.