Do-It-Yourself Sustainable Water Projects by Paul Dempsey

Author:Paul Dempsey
Language: eng
Format: epub
Publisher: McGraw Hill LLC
Published: 2013-01-15T00:00:00+00:00

Figure 5-2. A jet pump mounts either directly on the wellhead or at some distance from it. Both installations require a downhole foot valve (not shown) that closes to prevent water from draining out of the drop pipe when the pump stops. An offset pump has two provisions for priming—a priming plug on the pump casing and a pipe plug on the drop pipe tee. A check valve just downstream of the pump intake assures that the impeller retains prime. Wisconsin Department of Natural Resources

Figure 5-3. A jet pump schematic. The venturi increases the velocity of the drive water stream while reducing its pressure. Government of Alberta, Agriculture and Rural Development

The water in the well is under atmospheric pressure. As the drive water passes through the venturi, it speeds up and, at the same time, loses pressure. Well water, responding to the pressure differential, flows into the pump. Because atmospheric pressure is only 14.7 psi, a pump that develops a perfect vacuum at its intake port would lift only 34 ft. The partial vacuum generated by real-world jet pumps limits lift to about 20 ft.

Jet pumps provide an inexpensive and reasonably reliable means of extracting water from shallow depths. Surface mounting—either on the wellhead or offset some distance from it—is a great advantage, especially for homeowners who do their own maintenance. Some manufacturers market integrated systems with the pump, pressure tank, valves, and controls already plumbed and wired. Such consumer-oriented products simplify installation. Better systems can be built by shopping around for quality components and assembling them yourself.

Pump output and pressure depend upon motor horsepower and well depth. For example, the Sta-Rite HCL ½-hp unit delivers 11.7 gpm at 30 psi from a 15-ft well. If we increase the pressure to 50 psi, output drops to 6.1 gpm. Increasing well depth to 20 ft reduces output by 25 percent.

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