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.

Some History

The earliest windmills were used in Persia more than 2,000 years ago for the grinding of 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, to pump water, and to 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, including Aermotor, Dempster and Flint & Walling. Aermotor and Dempster still manufacture windmills.

Table 2.

How They Work

The 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 further 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 adjusting 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 up and down vertically, 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 upstroke, and a check valve in the plunger opens on the downstroke, allowing the plunger to return to the bottom of the cylinder without displacing any water. On the next upstroke, the first charge is expelled out of the cylinder up into the drop pipe, etc.

At a wind speed of 15 miles to 20 miles per hour, an 8-foot-diameter windmill working with a 3 1⁄2-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.

Table 1.

How to Select a Windmill

The following information is provided as 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 5 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; in 10-mph winds, about 38 percent. If prevailing winds are low, the use of a cylinder smaller than shown will permit your mill to operate in lower winds.

Sources of Supply

Check the Internet for additional sources of windmills and supplies.

Windmill manufacturers:

Aermotor Windmill Corp.
4272 Dan Hanks Lane
San Angelo, Texas 76901
Phone: 325-651-4951

Dempster Industries
711 South 6th Street
P.O. Box 848
Beatrice, Neb. 68310
Phone: 402-223-4026

Cylinder manufacturers and suppliers:

American Granby
7645 Henry Clay Blvd.
Liverpool, N.Y. 13088
Phone: 800-776-2266

Baker Manufacturing
133 Enterprise Street
Evansville, Wis. 53536
Phone: 800-356-5130

Dempster Industries
711 South 6th Street
P.O. Box 848
Beatrice, Neb. 68310
Phone: 402-223-4026

Maass Midwest
11213 Dundee Road
Huntley, Ill. 60142
Phone: 800-323-6259           

Midland Manufacturing Co.           
4800 Esco Drive
Fort Worth, Texas 76140
Phone: 817-478-4848


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….