Document 6w8j56GL7kYymZv70zJyOLp64

816 CHAPTER 31 1958 Guide adjoining section butting against the swage. The sections are held in place by rivets, sheet-metal screws, or by soldering. ' '' Rectangular ducts are generally constructed by breaking the corners and grooving the longitudinal seam, although some fabricators still use the standing seam. Elbows and transformation sections are' generally formed with.Pittsburgh comer seams because.this seam,is easier, to lock in place ___ 111. GROOVED SEAM STANDING SEAM Tji ~T|) h S SUP DRIVE SUP (jl^ END SUP OOUBLESCAM PITTSBURGH SEAM BAR SLIP M- - ANGLE SLIP REINFORCED BAR SLIP N POCKET SLIP ANGLE CONNECTION O FLUSH SEAM FAN DISCHARGE CONNECTIONS 1- - \ -^30* -- FAIR POOR HEATER, FILTER, AND WASHER CONNECTIONS than the double seam, but complicated fittings such as double-compounded elbows are usually constructed with double seam corners. The construc tions of these various seams, as well as the types of girth connections, are shown in Fig. 16. The application of the various slips and connec tions is outlined in Table 9. The end slip may be used wherever S slips are recommended. Where drive slips are used, the end slip may be ap plied on the narrow side of the duct, and the drive slips on only the maxi mum side. Designs M to P of Fig. 16 are for flush type seams on ductwork where Air Duct Design 817 joints are to be concealed. For smooth appearance the seams may be soldered flush or filled with auto-body filler. Screws or rivets used should be of flat-head type. Ducts 25 to 30 in. in size should be reinforced between the joints, but not necessarily at the joint. Ducts 31 in. and up should be reinforced at the joint and between the joints; if drive slips are used the angles are usually riveted to the duct about 2 in. from the slips. It is good practice Table 9. Recommended Sheet Metal Gages fob Rectangulab Duct CONSTBUCTION* Alu minum B.4S. Gage Steel U. S. Std. Gage Maximum Side, Inches Type of Transverse Joint Connections^ Bracing 24 26 Dp12to S.7Dfrtiv1e0,inP.occkeentteorrsBar Slips, on None 22 24 13 to 24 S,7Dfrtiv1e0,inP.occkeentteorrsBar Slips, on None 25 to 30 S,SDlirpivse, ,on1 i7n.ftPo10ckinet. ocren1tienr.sB0 ar 41 fxt 1froxmf ijno.inatngles 20 22 31 to 40 DrSivlieps, ,1oinn.7 Pftoc1k0eitn.orce1nitner.sB0 ar 41 fxt1frxomf ijno.inatngles 41 to 60 IfP7Iinfof.ticnAkJ.eOnxtgilonfer.iCnIcof.ennbintnae.errscBrteiaoirnnfSso,lriopcrsin1wg$ iiotnhn. 4Ifftx fIrfoxmfjioni.natngles . 20 61 to 90 1$3iInfifn.tx.P9A|oinncin.gk.meletbaaoCxriromrnIeunfimneifcnoct.ierocnBnitnseag,rrsoSwrliipt1hs$ 2Iffiantxn.fgIralofenmsgx,lefjoosriinnI.ft dxiaIgfonxafl 16 18 91uapnd 2 i9Pinfo. cxAiknnfe.gtilneom.raCbIxofainmrinnuree.mciBntiofcaonerrsncSitneolgirrps?s11w$3iintfht. I2faifnxtn.gIfrlafeonsmxg,lefojsroiniIn.ftdxiaIgfonxa}l terns wu pressures and velocities (see Table 6) utilised in typical ventilating and air conditioning sys- jyjT'. special rigidity or stiffness is required, ducts should be constructed of metal two gages heavier. j!r., ducts 18 in. and larger should be cross-broken. Cross-breaking may be omitted on uninsu- iated ducta d two gages of heavier metal are used. c ^her joint connections of equivalent mechanical strength and air tightness may be used, joints invested*113 * ^ in. may ^ use<i with bracing angles omitted, instead of 7 ft 10 in. lengths with Ducts 91 in. and larger require special field study for hanging and supporting methods. to cross-break or kink all flat surfaces to prevent vibration or buckling ue to the air flow and accompanying variations in internal pressure. construction of elbows and changes of shape cannot be definitely utnned, because of the varied conditions encountered in the field, but in general, long radius elbows and gradual changes in shape tend to maintain unuorrn velocities accompanied by decreased turbulence, lower resistance u a minimum of noise. ro,Heavy canvas connections (asbestos cloth if there is a fire hazard) are omjuended on both the inlet and outlet to all fans. Self-vulcanizing