Question 9.21: Total Dynamic Head for a Well. What pumping head would be re......
Total Dynamic Head for a Well. What pumping head would be required to deliver 4 gpm from a depth of 150 ft. The well is 80 ft from the storage tank, and the delivery pipe rises another 10 ft. The piping is 3/4-in. diameter plastic, and there are three 90º elbows, one swing-type check valve, and one gate valve in the line.
The total length of pipe is 150 + 80 + 10 = 240 ft. From Table 9.18, the three ells add the equivalent of 3 × 2.0 = 6 ft of pipe; the check valve adds the equivalent of 5.0 ft of pipe; the gate valve (assuming it is totally open) adds the equivalent of 0.5 ft of pipe. The total equivalent length of pipe is therefore 240 + 6 + 5 + 0.5 = 251.5 ft.
From Table 9.17, 100 ft of 3/4-in. pipe at 4 gpm has a pressure drop of 4.2 {ft}/{100^{\prime}} of tube. Our friction-head requirement is therefore 4.2 × 251.5/100 = 10.5 ft of water.
The water must be lifted 150 + 10 = 160 ft (static head). Total head requirement is the sum of static and friction heads, or 160 + 10.5 = 170.5 ft of water pressure.
| TABLE 9.18 Friction Loss in Valves and Elbows Expressed as Equivalent Lengths of Tubeª | |||||||
| Fitting | 0.5 in. | 0.75 in. | 1 in. | 1.5 in. | 2 in. | 3 in. | |
| 90-degree ell | 1.5 | 2.0 | 2.7 | 4.3 | 5.5 | 8.0 | |
| 45-degree ell | 0.8 | 1.0 | 1.3 | 2.0 | 2.5 | 3.8 | |
| Long sweep ell | 1.0 | 1.4 | 1.7 | 2.7 | 3.5 | 5.2 | |
| Close return bend | 3.6 | 5.0 | 6.0 | 10.0 | 13.0 | 18.0 | |
| Tee—straight run | 1.0 | 2.0 | 2.0 | 3.0 | 4.0 | ||
| Tee—side inlet or outlet | 3.3 | 4.5 | 5.7 | 9.0 | 12.0 | 17.0 | |
| Globe valve, open | 17.0 | 22.0 | 27.0 | 43.0 | 55.0 | 82.0 | |
| Gate valve, open | 0.4 | 0.5 | 0.6 | 1.0 | 1.2 | 1.7 | |
| Check valve, swing | 4.0 | 5.0 | 7.0 | 11.0 | 13.0 | 20.0 | |
| ªUnits are feet of pipe for various nominal pipe diameters. | |||||||
| TABLE 9.17 Pressure Loss Due to Friction in Plastic Pipe, Feet of Water per 100 ft of Tube for Various Nominal Tube Diameters |
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| gpm | 0.5 in. | 0.75 in. | 1 in. | 1.5 in. | 2 in. | 3 in. |
| 1 | 1.4 | 0.4 | 0.1 | 0.0 | 0.0 | 0.0 |
| 2 | 4.8 | 1.2 | 0.4 | 0.0 | 0.0 | 0.0 |
| 3 | 10.0 | 2.5 | 0.8 | 0.1 | 0.0 | 0.0 |
| 4 | 17.1 | 4.2 | 1.3 | 0.2 | 0.0 | 0.0 |
| 5 | 25.8 | 6.3 | 1.9 | 0.2 | 0.0 | 0.0 |
| 6 | 36.3 | 8.8 | 2.7 | 0.3 | 0.1 | 0.0 |
| 8 | 63.7 | 15.2 | 4.6 | 0.6 | 0.2 | 0.0 |
| 10 | 97.5 | 26.0 | 6.9 | 0.8 | 0.3 | 0.0 |
| 15 | 49.7 | 14.6 | 1.7 | 0.5 | 0.0 | |
| 20 | 86.9 | 25.1 | 2.9 | 0.9 | 1.0 | |