Document O1e53ynxXdZ67nEaKRbn4Y3nv

HEATING VENTILATING AIR CONDITIONING GUIDE 1942 Grooved seam if Double seam Standing seam Pittsburgh Seam S sl'P Bar slip Angle connection. Angle |r slip CHAPTER 32. AIR DUCT DESIGN maximum side. 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 to cross-break or kink all flat surfaces to prevent vibration or buckling due to the air flow and accompanying variations in internal pressure. Round ducts are sometimes swedged 1.5 in. from the ends so that the larger end will butt against the swedge and are held in place with sheet metal screws. Where swedges are not used it is general practice to paste the joint with asbestos paper to insure a tight joint. The construction of elbows and changes of shape cannot be definitely outlined because of the varied conditions encountered in the field, but in 626 627