| Table of Pumping Capacities
| This chart if for a 1-7/8" pumping cylinder
| Pumping Capacity: 3 gallons per minute (GPM)*
Elevation (in feet)
| 8 Foot
| 10 Foot
| 12 Foot
| 14 Foot
| 16 Foot
|* 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.