Alternative Pumping Systems: Windmills
Windmills have been used for pumping water for hundreds of years, and they remain a viable alternative to electrically driven pumps in remote areas. This article will present a brief history of windmills, describe how they work, offer some guidelines and rules of thumb for sizing and designing windmill systems, and list some sources of supply for windmills and windmill components.
A Brief HistoryThe earliest windmills were used in Persia more than 2,000 years ago for grinding grain. They subsequently spread throughout the Middle East and were brought to Europe by the Crusaders in the 13th century. In Holland, windmills were used to drain marshes, pump water and drive the machinery used for milling grain, sawing wood and producing paper.
Windmills were adopted for pumping water in North America by the middle of the 19th century. Their use declined drastically in the 1930s when inexpensive electricity reached the rural areas. Several of the major pump manufacturers making electrically driven pumps today began as windmill manufacturers during the last century, including Aermotor, Dempster and Flint & Walling. Aermotor and Dempster still manufacture windmills.
How They WorkThe common water-pumping windmill consists of a tall metal or wooden tower with a rotor on top having up to 20 blades mounted on a horizontal shaft. A tail-vane keeps the rotor facing into the wind by swiveling the whole assembly. Windmills are self-regulating by design as follows. The main shaft of the rotor wheel is slightly offset from the centerline through the vane and pump rod. A regulating spring between the frame and vane holds the rotor wheel perpendicular to the wind (open) until the force of the wind on the rotor wheel overcomes the spring tension, and the wheel begins to close. As the wind velocity increases, the wheel closes farther until it is almost parallel to the vain. Then, when the wind velocity decreases, the wheel opens again by the force of the regulating spring. The wind speed at which the wheel begins to close is adjustable by modifying the spring tension. In addition, the wheel can be manually closed from the ground by actuating a ground level lever. The lever can be connected to a float in a storage tank to automatically close the wheel.
A set of gears and linkages connects the main shaft to the pump rod (also known as the pump pole or sucker rod), which moves vertically up and down, and extends into the well where it is coupled to a cylinder located below the water level. The cylinder consists of a plunger and two check valves. The up and down motion of the plunger draws water into the cylinder on the up stroke, and a check valve in the plunger opens on the down stroke, allowing the plunger to return to the bottom of the cylinder without displacing any water. On the next up stroke, the first charge is expelled out of the cylinder, up into the drop pipe, etc. (see Figure 1).
At a wind speed of 15 mph to 20 mph, an 8-foot diameter windmill working with a 31⁄2-inch cylinder will lift 10 gallons of water per minute to a height of 50 feet above the water level in the well. That same mill coupled to a 2-inch cylinder will pump 3 gpm at 140 feet of total head (Table 2 shows the pumping capacities of various windmill/cylinder combinations).
How to Select a WindmillThe following information is provided a general guide. Ask your windmill dealer to assist you in choosing the equipment to meet your specific needs.
1. Calculate the average daily water consumption by using Table 1. As you can see, a sheep ranch would be a better place to have a windmill than a dude ranch (unless you had very few dudes).
2. Divide the average daily water consumption by 5 to arrive at equivalent hourly pumping capacity required from your mill. This is based on wind conditions permitting the mill to pump the equivalent of five hours of rated capacity per day. This varies widely by locality and time of year.
3. Choose the cylinder diameter that is closest to the equivalent hourly pumping capacity from Table 2.
4. Calculate the total pumping elevation from the water level in the well to the point of discharge.
5. Choose the size mill to operate the cylinder when pumping to the total elevation from Table 2.
6. Choose a tower that will place the center of the wheel at least 15 feet above wind obstructions within a radius of 400 feet.
7. Choose a cylinder with a stroke at least 2 inches longer than the pumping stroke of the mill. The mill manufacturer's specifications will give you the mill's stroke for the particular machine you choose.
8. Choose pump rod, pipe and other accessories according to the specific cylinder you are using.
The capacities in Table 2 are approximate, based on the mill set on long stroke (mills typically have two stroke settings - long and short), and operating in a 15-mph to 20-mph wind. Using the short stroke setting increases lift one-third and reduces capacity one-fourth. In a 12-mph wind, capacity is reduced 20 percent, and in 10-mph winds, about 38 percent. If prevailing winds are low, using a cylinder smaller than shown will permit your mill to operate in lower winds.
Sources of SupplyWindmill Manufacturers: Dempster Industries
711 South 6th Street
P.O. Box 848
Beatrice, Neb. 68310
Aermotor Windmill Corp.
4272 Dan Hanks Lane
San Angelo, Texas 76901
1701 E. 3rd
Amarillo, Texas 79120
Cylinder Manufacturers and Supplies:
7645 Henry Clay Blvd.
Liverpool, N.Y. 13088
133 Enterprise Street
Evansville, Wis. 53536
711 South 6th Street
P.O. Box 848
Beatrice, Neb. 68310
11213 Dundee Road
Huntley, Ill. 60142
Midland Manufacturing Co.
4800 Esco Drive
Ft. Worth, Texas 76140
In conclusion, windmills are relatively inexpensive water pumps, are easy to maintain (change the oil in the gear box once a year), and can be a reliable source of water if the wind blows consistently where you are located. If your pumping requirements fall somewhere on Table 2 and the use of an electrically powered pump is not feasible, contact one of the companies listed above to discuss your application.
Next month, we will continue our discussion of “alternative pumping systems” with a look at solar pumps. 'Til then ….