Document VGqN7142mvymG0aRE7RNdmvvq
American Society of Heating and Ventilating Engineers Guide, 1928
Table 5. Frictional Resistance of Straight Conveyor Pipe To Flow of Air Per 100 Feel of Pipe
Vel. op Air
in Ft. per Min.
2000 2200 2400 2600 2800 3000 3200 3400 3600 3800 4000 4200 4400 4800 5200 5600 6000
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Loss op Pressure in Inches for Given Diameter Pipe
4'
1.92 2.32 2.77 3.26 3.76 4.33 4.93 5.56 6.23 6.95 7.69 8.48 9.26 11.05 13.00 15.25 17.30
5'
1.53 1.85 .2.22 2.60 3.01 3.46 3.94 4.45 4.98 5.55 6.15 6.78 7.41 8.85 10.50 12.05 13.85
6'
1.28 1.55 1.84 2.17 , 2.52 2.88 3.28 3.71 4.15 4.62 5.13 5.65 6.18 7.38 8.66 10.05 . 11.52
7'
1.09 1.32 1.58 1.86 2.15 2.47 2.82 3.18 3.56 3:97 4.40 4.85 5.30 6.32 7.44 8.61 9.89
8'
0.962 1.16 1.39 1.63 1.89 2.08 2.47 2.78 3.12 3.48 3.85 4.25 4.63 5.55 6.50 7.55 8.66
10'
0.770 0.932 1.01 1.30 1.51 1.73 1.97 2.22 2.49 2.78 3.08 3.49 3.71 4.43 5.21 6.03 6.92
12'
0.640 0.778 0.924 1.08 1.26 1.44 1.64 1.85 2.08 2.32 2.57 2.83 3.09 3.69 4.34 5.05 5.76
14' 16' 18' 20' 22' 24' 30'
2000 2200 2400 2600 2800 3000 3200 3400 3600 3800 4000 4200 4400 4800 5200 5600 6000
0.550 0.655 0.790 0.930 1.07 1.24 1.41 1.59 1.78 1.99 2.20 2.43 2.66 3.17 3.72 4.32 4.95
0.482 0.582 0.693 0.810 0.932 1.08 1.23 1.43 1.56 1.74 1.92 2.12 2.33 2.77 . 3.25 3.78 4.33
0.428 0.578 0.617 0.722 0.838 0.961 1.09 1.24 1.38 1.54 1.71 1.88 2.06 2.46 2.89 3.35 3.85
0.385 0.465 0.553 0.650 0.754 0.865 0.985 1.11 1.25 1.39 1.54 1.70 1.85 2.22 2.61 3.02 3.46
0.350 0.423 0.504 0.590 0.685 0.788 0.895 1.01 1.13 1.26 1.40 1.54 1.68 2.02 2.36 2.74 3.14
0.320 0.388 0.462 0.542 0.628 0.722 0.820 0.925 1.04 1.16 1.28 1.42 1.54 1.85 2.16 2.52 2.89
0.257 0.310 0.369 0.434 0.503 0.577 0.657 0.742 0.832 0.926 1.03 1.13 1.24 1.48 1.75 2.01 2.31
FRICTIONAL RESISTANCE OF ELBOWS
Elbows having a throat radius equal to the pipe diameter set ^ip a resistance equivalent to a section of
straight pipe approximately 20 diameters long. With a throat radiusof 1% times the diameter the resistance
is about the same as seven diameters of straight pipe.
'
The usual types of ventilating fans are unsuitable for exhaust systems which are required to handle materials such as shavings, sawdust, emeiy dust, etc. Higher pressures are required than in ventilating work and in addition housings and blast wheel must be so constructed that the . materials.handled do not deposit in same. While the fans used in different exhaust systems are more or less of the same general type, modifications are frequently necessary to fit them for handling such materials as long shavings, strips.of paper, cotton, pulverized coal, etc.
The most common method of separating the dust and other materials from the air is to pass the mixture through a centrifugal or "cyclone"
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Chapter XXVI--Dust,' Exhaust and Collecting Systems
collector. In this type of collector the mixture of the air and material is introduced on a tangent, near the cylindrical top of the collector, and the whirling motion sets up a centrifugal action causing the compara tively heavy materials suspended in the air to be thrown against the side of the separator, from which position it spirals down to the tail piece, while the air escapes through the stack at the center of the collector.
COLLECTORS
For most systems, the nominal size and number of. the collector will be the same as the diameter in inches of the main pipe leading to it. The nominal sizes of the different makes of collectors vary greatly, and it
Fig. 1. Collectors on Roof Piano Factory
is advisable to make sure that a collector is large enough to do the work without excessive pressure drop, irrespective of nominal number or size. The larger the collector within certain limits the better will be the separa tion, and the less will be the back pressure on the fan and power consumed.
Special construction is sometimes required for fine dust, also some blow pipe manufacturers use a special type of collector for furnace feed, the object being to deliver the material to furnaces as uniformly as possibly.
When more than one fan delivers into a single collector a back pressure
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