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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.

Example 9.21
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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
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

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