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726 CHAPTER 52 1960 Guide Table 5 .... Exhaust Requirements2* for Grinding, Polishing, Buffing, Scratch Brushing Abrasive Cut-Off Wheels, Grinding and Polishing Belts (Air Volume: 4500 fpm in at) branches.) (2-in. voter suction of Orerag* hood.) Wfa*et (dia), bv Max. Brandi Width* <M fa. to. Cfm Wheal (dia), to. Max Brandi Width* (dia). In. In. Cfm -9 10-16 17-19 20-24 25-30 31-36 lH 2 3 4 5 6 3 225 4 390 -9 4M 500 10-16 5 610 17-19 6 880 20-24 7 1200 25-30 2 3 4 5 6 34 300 44 500 5 610 54 740 6.4 1010 Horizontal Single Spindle Dire Grinder* Horizontal Ooubfe Vortical Single Spindle Spindle Disc Grinder* Kk Grinder* Wheel Brandi (dia) (dia) bv In. Cfm Wheel Brandi (dia) (dial bv In. Cfm Wheel Brandi (dia) (dia) bv bv Cfm -12 13-:19 20-30 31-36 3 4 5 6 225 -19 1-5 610 -20 1-44 500 390 20-25 1-6 880 21-30 2-4 780 610 26-3C 1-7 1200 31-53 2-6 1760 880 31-53 2-6 1760 54-72 2-8 3120 54-72 4-8 6240 Gbinding or Poushing Belts: To 3 in- wide--3 in. branch, add H in- to branch diame ter for each 2 in. or fraction increase in belt width over 3 in. C'lQ.rj w.*iw puct eho V,:0.*F V:L7e, cia.o fVAWGgppucT etA**.n>ctP two Miner *? * 5 o:>Q*-i fS-rUeV,A* [tV V,.*.*.0UCT ffeSSSW a*n.BvcT ciu --------' ci0.ez 5 tmSSSSSc | vo.esFv eiXTe a 5 * Mute 11 tSensve^reScsj v r * 0oas*,cwer 828111 c*"t *a r >(wnrr loss facto* jjai i n.sciacrrr Hvsvw w duct, m voter 5^ a* static Mtesum or TinooT. n vatia i>omrr loss, w nre a o* volume,enr .* cnoss sectiok at throat, so rr C*mrrKSm or tttnrr orntr vos* roe eoteucorcB wae shams lbkak mxo mo smpve od^omcmts Z. CALCULATE u ran EACH COMPONENT S.AOO wucs or L. era hoods FLANGED TcAMuCqIAxJ EcJAirTtCocOmT*vAeEcC-- mood rjrrerr loss --***-" * HOODS. -aU_> LXm- m- uki * ixrcxMj a (loss) Tape* a ivoss) ofcrew k wiutw : r_eaocrrrotrMocosr axnocltet* nu. tcrtriown wor i "5" nourrf^tANCTO i.eo as o n DCCCLCnxnoM loSS a RCCAM ACCELERATION LOS s the air flow. For conveying of solid particles, velocities shown in Table 8 include a reasonable factor of safety and, consequently, design velocities may therefore be ad justed as required to permit use of commercial pipe sizes that are available generally in Vt-in. diameter steps through 6-in. diameter, 1-in. steps through 16-in. diameter or larger, and 2-in. diameter steps for large diameters. For contaminants other than solids, conveying velocities are based on a consideration of the higher resistance and lower first cost of smaller diameter ducts against higher first cost and lower resistance of larger diameter ducts. Main ducts connecting two or more branches are sized by the same procedure as for branches. The main should be designed for the total exhaust volume to be handled through all branch ducts. Where exhaust systems handling solids are to provide for a substantial increase of future capacity, required conveying velocities can be maintained by: 1. Providing open end stub branches in the main through which air will be admitted into system until future connection is made. The volume admitted into the main can be adjusted to required air flow rate (cfm) by use of a blast gate or orifice plate in such stub branch. 2. Arranging the system layout so that exhaust from future points can be picked up by a separate main that will run directly to the tan or air cleaning equipment inlet. CALCULATION OF SYSTEM PRESSURE LOSS The pressure loss of the system includes entrance loss0 as air is accelerated through the hood to a branch duct connection, resistance losses of ducts," elbows, and junc tions, and acceleration or deceleration losses from ve- Taporod hood data from Reference 43. WeofWbood data from Reference 44 Fig. 2 .... Exhaust System Design Data14 locity changes within the system. Chapter 21 includes data on duct resistance and on resistance of elbows, and provides sample calculations. In exhaust systems, either the equal friction method (illustrated in Chapter 21) or the use of blast gates in the branches to equalize pressure loss of all runs is employed.'* "* "" Data on losses for hood entrance, branch entry, transi tions, and weather hoods are given in Fig. 2. The static pressure in branch ducts close to the hood connection is frequently referred to as hood suction. It is the sum of the branch velocity pressure and the hood entrance loss. CONSTRUCTION SPECIFICATIONS FOR LOCAL EXHAUST SYSTEMS Correct design and competent installation of sheet steel ducts and hoods, are necessary for the proper functioning of any exhaust system. The following specifications are tho6e recommended in the Industrial Feniiiatitm Manual.a General All exhaust systems shall be constructed with the materials recommended herewith and shall be installed in a permanent IMEasao. Industrial Exhaust Systems 727 Table 6 ... .Ventilation Rates for Open Surface Tanks**27 Minimum Ventdation Rate Cfm For Sq Ft Hood Openrap Hood Canopy Hood Minimum Ventilation Rate Cfm Per Sq Ft Tank Area Lateral Exhaust (Note f) W/L = TIBanMk WWi.dOtTh Tank Length One Open Two Open Three Open Foot Open W/L 0-0.24 Side Side* Side* Sides AB W/L 0.250.49 AB W/l 0.50- 1.0 AB Process Minimum Ventilation Rate Cfm Per Sq Ft Hood Opening Matimum Ventilation Rate Cfm Per Sq Ft Tank Area Lateral fxfiavtf (Mote 1) W/L - Enclosing ' Hood Canopy Hood Tank Length One Open Two Open Three Open Four Open W/l 0-0.24 Side Side* Side* A W/L 0.250.49 A W/L 0.50- 1.0 A fi Plating Chromium (Chromic Acid Mist).. Arsenic (Ar sine) ........... Hydrogen Cy anide........... Cadmium.... 75 65 75 75 Anodizing......... 75 100 125 175 125 175 150 200 175 225 90 100 150 90 130 110 150 130 170 100 125 175 125 175 15C 200 175 225 100 125 175 125 175 154 200 175 225 100 125 175 125 175 15C 200 175 225 Metal Cleaning (Pickling) Cold Acid....... Hot Acid........ Nitric and Sul furic Acid... Nitric and Hy drofluoric Acid.............. 65 75 75 75 no90 100 150 90 130 150 130 170 100 126 175 125 175 150 20C 175 225 100 125 175 125 175 150 200 175 225 100 125 175 125 175 150 200 175 225 Metal Cleaning Note 2 and Ref. 38 and 39 Metal Cleaning (Caustic or Electrolytic) Not Boiling Boiling........ Bright Dip (Nj trie Acid) Stripping Concentrated Nitric Acid. Stripping Cone. Nitric end SnJ- furic Acid... 75 100 125 175 125 175 150 200 175 225 Salt Baths (Molten Salt).. .. 50 75 75 125 60 90 75 100 90 110 Salt Solution (Parkerize. Bonderize, etc.) Not Boiling. .. Boiling................ 90 75 90 100 150 90 130 110 150 130 170 100 125 175 126 175 150 200 175 225 Hot Water (if vent, desired) Not Boiliog. Boiling............ 50 75 no75 75 125 60 90 75 100 90 100 125 175 125 175 150 200 176 `225 Not* 1--Column A refers to teak with hood stoat one side or two penile! sides when obo hood b afloat e veil or e beffle ronnint length of tank end ss high es tank a vide; also to teaks with exhaust "ArM along center tine with ? tank width in W/L Retie f/slnmn B refers to free standing tank with hoodalong one side or two parallel tides. Note 3--Complete control of the vapors end mist from degreasing operations requires the came veatiletioe rales as recommended for pickling. However, the solventa employedin degreasing operations ererelatively volatile, and the solvent loss caused by evaporation iaoeaaes rapidly es the erhaqst rate at the tank inaeaeee. For this reason perfect control is usually sacrificed in favor of lover solvent evaporation rates. Where solvent loss does not present an important cost or operating problem, the exhaust rates given for pickling should be adhered to, but wlmre solvent lass most be kept at s mlirinuim, an exhaust rate of 60 cfm per eq 11 of tank area is commonly employed. Where this rate is used, control will be adequate only if the tank is located in an area free at draft* and if the degreesing operations are anted out in accordance with a rigid schedule." and workmanlike manner. The interior of ail ducts shall be smooth and free from obstructions; with joints either welded, flanged, or soldered airtight. Materials 1. Ducts shall be constructed of block iron welded or of galvanized sheet steel riveted and soldered unless the presence of corrosive gases, vapors, and mists or other conditions make use of such material impracticable. Galvanised construction is not recommended for temperatures exceeding 400 F. Welding of black iron of 18 gage and lighter is not recommended for field fabrication. . 2. For average exhaust systems on non-corrosive applications the following metal thickness shall be supplied: Diameter of Straight Oud* (Indies) U. S. Standord Gage for Steel Dud Oats 1 OCR* II Oats til Up to 8......................... Over 8 to 18................. Over 18 to 30............... Over 30......................... / 24 22 20 18 22 20 20 18 18 16 16 .14 Class 1. Includes non-abrasive applications such as paint spray, woodworking, pharmaceutical and food product, ana dis charge ducts from dust collectors. Class II. Includes applications for non-abrasive material in high concentration (low-pressure pneumatic conveying); mod erately abrasive material; and highly abrasive materials in light concentrations. Typical applications are conveying of chemicals and wood dust; exhaust of foundry shakeouts and sand handling systems, gram dusts; coal crushing and screening; exhaust of gnt blast cabinets; and grinding, buffing, and polish- U1^'Class III. Includes applications for all highly abrasive ma terials in moderate to heavy concentrations and moderately abrasive materials in heavy concentrations such as low-pressure conveying of tobacco; exhaust systems from sand and grit blast ing and abrasive cleaning operations, from rock and ore screen ing and crushing, from dryers and kilns, and fly ash removed from boiler stacks. Where aluminum duct is indicated, the following equivalent B A S gage thickness of sheets should be used: Steef-U. 8. Standard Gage 26 24 22 20 18 16 14 Aluminum--B A S Gage 24 22 20 18 16 14 12 3. For exhaust systems on corrosive applications, considera tion should be given to non-corrosive materials or coatings. (Continued on p. 729) /