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How to size the mill to your well...
Step 1: Have your well drilled.
Step 2: Record the total well depth and the static water level.
Step 3: Determine how high above the well you will need to discharge the water.
EXAMPLE
Well Depth: 200 feet
Static Water Level: 150 feet
Discharge above well: 10 feet
Total Lift: 160 feet (150+10)

Using the information in the example, look at the following chart:

Table of Pumping Capacities
This chart if for a 1-7/8" pumping cylinder
Pumping Capacity: 3 gallons per minute (GPM)*
Wheel
Diameter
Pumping
Elevation (in feet)
  Long Stroke Short Stroke
8 Foot 175 233
10 Foot 260 346
12 Foot 390 519
14 Foot 560 745
16 Foot 920 1224
* In a 18 to 20 Mile Per Hour (MPH) wind
The proper windmill head diameter for the example is an 8 Foot head assuming you use a pumping cylinder with a 1-7/8" diameter. You should always size a windmill on the depth the windmill will pump using the long stroke. You can switch to the short stroke if the static water level in the well drops below the maximum depth from which the windmill head will pump. Using the short-stroke, the water production decreases by 25% (from 3 GPM to 2.25 GPM) and pumping elevation increases by 33% (from 175 to 233 ft).

Optimum tower height is determined by the location of the windmill with respect to the surrounding structures.

To obtain the optimum performance from your windmill, it should be located 400 feet from the nearest structure and the top of the tower should be 15 feet taller than the tallest surrounding structure. This is if it were a perfect world. Sometimes the well must be drilled in a less than optimum location. Purchasing the tallest tower your pocket book can afford to allow the windmill head to clear the top of the nearest sturcture(s) in the path of the prevailing wind is recommended.

Lets add to the example. We know we have 160 feet of lift and lets say you have a single story house to the north of the water well and a small barn/workshop that is on the south side of the water well. Lets also assume that the wind is normally from either the south or the north. Lets say that the top of the tallest structure is 18 feet tall. Using this information the shortest tower that should be used is a 33 foot tower.

A water pumping windmill will produce a minimum of 3 gallons per minute (GPM) in a 18 to 20 MPH wind. This is assuming that the pump (working barrel) in the bottom of the well is a 1-7/8" diameter cylinder that is connected to 2" drop pipe. You can get a greater production of water if you use a larger cylinder and larger pipe. Click on the link at the top of this page to see an expanded depth chart. You will also need a larger windmill head to lift the larger amount of water. Your need for more water will come at a greater initial expense.

You can also use a closed top cylinder (which connects to pipe smaller than the diameter of the cylinder) but remember, when the time comes to change the leathers on the valves in the cylinder, with a closed top cylinder, you have to pull the rod AND the pipe at the same time. With an open top cylinder, you only need to pull the rod. Let the depth of your well determine the type of cylinder you will use.

If all this is confusing, after you get your well drilled, give me a call and I will be happy to help you.



Photos | usedWindmillParts.com
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