Document gD9ddz81jRb2kn4z2xgGNYR0N

HEATING VENTILATING AIR CONDITIONING CUIDE 1944 general long radius elbows and gradual changes in shape tend to maintain uniform velocities accompanied by decreased turbulence, lower resistance and a minimum of noise. Heavy canvas connections are recommended on both the inlet and outlet to all fans. The fan discharge connections shown in Fig. 7 are Grooved Standing seam S slip Drive slip "P "T -A--J*.-J- Double seam Pittsburgh seam Bar slip Reinforced !' slip Pocket slip End slip Angle connection CHAPTER 32. AIR DUCT DESICN in the duct size in order to maintain as nearly uniform velocity as possible. Branch take-offs should always be arranged to cut or slice into the air stream in order to reduce as far as possible the losses in velocity head. The recommended gages for sheet metal duct construction are given in Table 5. Weights of sheet metal per square foot of surface for different gages are given in Table 6. The weights of various gages and the areas Fig. 7. Sheet Metal Duct and Arrangement Details marked good, fair, and poor in the order of the amount of turbulence produced. An inspection of the heater connections shown in Fig. 7 will readily show that uniform velocity through the heater cannot be expected in the diagram noted poor. When obstructions cannot be. avoided, the duct area should never be decreased more than 10 per cent and then a streamlined collar should be used. Larger obstructions require an increase 612 for any length of run of rectangular sheet metal ducts may also be determined from Fig. 8. The bottom scale represents the sum of the two sides of the duct and the oblique lines give the length of run in feet. Proceeding horizontally to the right from the intersection of vertical and oblique lines on the chart, the area of the duct may be determined in the first vertical scale. The scales to the right give the weights of the duct run for different gages of metal. In calculating the weights <?f duct, it 613