Example. A seed cleaning house is to install a hood over each machine exhaust dust arising from the cleaning operation. A schematic plan of the system is shown in Fig. 29. The steps to follow are:
1.Determine the pressure drop between the system outlet and the hood the greatest distance from the outlet. The optimum velocity in the pipe will control the pressure. In this case, 1000 ft. per min is considered desirable. The dust and dirt which will be removed is finely divided and will remain suspended at this velocity.
Hood D is the greatest distance from the datum R. Consider a single 8-in. pipe between these points since the velocity will be approximately 1000 ft. per min to deliver 300 cu ft. per min. The single elbow resistance may be considered equivalent to that of a length of pipe of 50 diameter or 33 ft., and the hood 20 diameters or 17 ft. The total effective length is 250 ft. The pressure drop between D and R determined by the previous procedure s 0.41 in. of water and is assumed to be uniform through this distance.