Where one has his own water supply, however, and it is necessary to lay pipe to secure the requisite fall, the problem is more difficult. Friction in pipes acts in the same way as cutting down the head a proportional amount; and by cutting down the head, your water motor loses power in direct proportion to the number of feet head lost. This head, obtained by subtracting friction and other losses from the surveyed head, is called the effective head, and determines the amount of power delivered at the nozzle.
The tables on pages 66-67 show the friction loss in pipes up to 12 inches in diameter, according to the amount of water, and the length of pipe.
In this example it is seen that a 240-foot static head is reduced by friction to 230.1 feet effective head. By referring to the table we find the wheel fitting these conditions has a nozzle so small that it cuts down the rate of flow of water in the big pipe to 4.4 feet a second, and permits the flow of only 207 cubic feet of water a minute. The actual horsepower of this tube and nozzle, then, can be figured by applying formula (A), Chapter III, allowing 80 per cent for the efficiency of the wheel. Thus:
To calculate what the horsepower of this tube 12 inches in diameter and 900 feet long, would be without a nozzle, under a head of 240 feet, introduces a new element of friction losses, which is too complicated to figure here. Such a condition would not be met with in actual practice, in any event. The largest nozzles used, even in the jumbo plants of the Far West, rarely exceed 10 inches in diameter; and the pipe conveying water to such a nozzle is upwards of eight feet in diameter.
PIPE FRICTION TABLES
INDICATING THE CALCULATED LOSS OF HEAD DUE TO FRICTION IN RIVETED STEEL PIPE WITH VARIOUS WATER QUANTITIES AND VELOCITIES
[Courtesy of the Pelton Water Wheel Company]
Heavy-faced figures = Loss of head in feet for each one thousand feet of pipe.
Light-faced figures = Water quantity in cubic feet per minute.
| Pipe Diameter | Velocity in Feet per Second | ||||||||||||
| 2.0 | 2.2 | 2.4 | 2.6 | 2.8 | 3.0 | 3.2 | 3.4 | 3.6 | 3.8 | 4.0 | 4.2 | 4.4 | |
| 17.1 | 20.0 | 25.6 | 28.3 | 32.0 | 37.3 | 40.9 | 45.8 | 50.4 | 56.0 | 62.3 | 68.1 | 74.9 | |
| 3" | 5.9 | 6.5 | 7.1 | 7.7 | 8.3 | 8.9 | 9.4 | 10.0 | 10.6 | 11.2 | 11.8 | 12.4 | 13.0 |
| 11.0 | 13.0 | 15.0 | 17.3 | 20.2 | 23.2 | 26.2 | 29.6 | 33.0 | 36.5 | 41.0 | 45.4 | 49.2 | |
| 4" | 10.5 | 11.5 | 12.6 | 13.6 | 14.7 | 15.7 | 16.8 | 17.8 | 18.8 | 19.9 | 21.0 | 22.0 | 23.0 |
| 7.7 | 9.4 | 11.0 | 12.9 | 14.9 | 16.9 | 19.5 | 21.6 | 24.0 | 27.0 | 29.8 | 32.9 | 36.0 | |
| 5" | 16.4 | 18.0 | 19.6 | 21.2 | 22.9 | 24.5 | 26.1 | 27.8 | 29.5 | 31.0 | 32.7 | 34.3 | 36.0 |
| 6.0 | 7.2 | 8.6 | 9.9 | 11.7 | 13.0 | 14.6 | 16.6 | 19.0 | 21.5 | 23.4 | 25.5 | 27.8 | |
| 6" | 23.5 | 25.9 | 28.2 | 30.6 | 32.9 | 35.3 | 37.7 | 40.0 | 42.4 | 44.7 | 47.1 | 49.5 | 51.8 |
| 4.9 | 6.9 | 7.0 | 8.1 | 9.3 | 10.6 | 12.0 | 13.6 | 15.2 | 17.0 | 19.0 | 21.0 | 23.0 | |
| 7" | 32.0 | 35.3 | 38.5 | 41.7 | 44.9 | 48.1 | 51.3 | 54.5 | 57.7 | 60.9 | 64.1 | 67.3 | 70.5 |
| 4.0 | 4.9 | 6.0 | 6.9 | 7.8 | 9.1 | 10.0 | 10.2 | 13.0 | 14.4 | 15.9 | 17.2 | 19.2 | |
| 8" | 41.9 | 46.1 | 50.2 | 54.4 | 58.6 | 62.8 | 67.0 | 71.2 | 75.4 | 79.6 | 83.7 | 87.9 | 92.1 |
| 3.4 | 4.2 | 5.1 | 5.9 | 6.7 | 7.7 | 8.9 | 9.8 | 11.0 | 12.2 | 13.8 | 15.0 | 16.0 | |
| 9" | 53.0 | 58.3 | 63.6 | 68.9 | 74.2 | 79.5 | 84.8 | 90.1 | 95.4 | 101 | 106 | 111 | 116 |
| 2.9 | 3.7 | 4.4 | 5.1 | 5.9 | 6.7 | 7.5 | 8.6 | 9.5 | 10.6 | 12.1 | 13.1 | 14.1 | |
| 10" | 65.4 | 72.0 | 78.5 | 85.1 | 91.6 | 98.2 | 105 | 111 | 118 | 124 | 131 | 137 | 144 |
| 2.6 | 3.2 | 3.8 | 4.4 | 5.1 | 5.9 | 6.6 | 7.5 | 8.4 | 9.5 | 10.3 | 10.1 | 12.5 | |
| 11" | 79 | 87 | 95 | 103 | 111 | 119 | 127 | 134 | 142 | 150 | 158 | 166 | 174 |
| 2.36 | 2.9 | 3.4 | 3.9 | 4.5 | 5.2 | 5.9 | 6.7 | 7.5 | 8.5 | 9.4 | 10.0 | 11.0 | |
| 12" | 94 | 103 | 113 | 122 | 132 | 141 | 151 | 160 | 169 | 179 | 188 | 198 | 207 |