2. Adjust the size of the trunk and laterals so that the pressure drop between each hood and the datum R is the same as in the longest line, 0.41 in. water. The drop in trunk 1-2 is 65/250 X0.41 or 0.107 in. of water.
To handle the 120 cfm., the diameter here must be 13 in.
The drop in trunk R-1 is 1/250 X 0.41 or 0.0164 in., and, to handle 1250 cfm., the diameter must be 13 in.
The pressure drop in line R-2 is (10 + 65)/250 of 0.41 or 0.123 in.
Therefore, the drop in line 2-C and 2-B must be 0.11 0.123 or 0.287 in Line 2-C is 60 ft. long and contains two elbows and a hood. The total elbow and hood resistance is 120 pipe diameters.
Trial-and-error procedure will show that a 74-in. pipe of equivalent length of 135 ft.
will give a pressure drop of nearly 0.287 in. when delivering 300 cu ft. per min.
The pressure drop in section 2-3 which includes the elbow at 2 would be
2. Adjust the size of the trunk and laterals so that the pressure drop between each hood and the datum R is the same as in the longest line, 0.41 in. water. The drop in trunk 1-2 is 65/250 X0.41 or 0.107 in. of water. To handle the 120 cfm., the diameter here must be 13 in. The drop in trunk R-1 is 1/250 X 0.41 or 0.0164 in., and, to handle 1250 cfm., the diameter must be 13 in. The pressure drop in line R-2 is (10 + 65)/250 of 0.41 or 0.123 in. Therefore, the drop in line 2-C and 2-B must be 0.11 0.123 or 0.287 in Line 2-C is 60 ft. long and contains two elbows and a hood. The total elbow and hood resistance is 120 pipe diameters. Trial-and-error procedure will show that a 74-in. pipe of equivalent length of 135 ft. will give a pressure drop of nearly 0.287 in. when delivering 300 cu ft. per min. The pressure drop in section 2-3 which includes the elbow at 2 would be
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