Session 7 Strengths and testing
TOTAL TIME: 2 Hours
OBJECTIVES: Familiarize participants with the strengths and
characteristics of the local materials.
Discover what is available in the way of local building
materials.
MATERIALS: Small poles, pipe, bamboo, and whatever materials you
wish to examine and test to use in wind system construction.
PROCEDURES:
Step 1: 30 minutes
Walk around the site looking at the types of materials available
for use. Comment on and discuss the uses, qualities, strengths and weaknesses of
the various types of materials represented.
Step 2: 15 minutes
Explain the method of destructive testing-pushing things to
their limits.
Step 3: 15 minutes
Test some poles by supporting them at varying distances
horizontally along their lengths and having someone stand on the middle of the
poles.
Step 4: 5 minutes
Make some educated guesses at the stresses involved.
Step 5: 30 minutes
Discuss the forces on a mill and give some idea of the size of
the forces-wind load and centrifugal load on the rotor and tower, as well as the
pump loads.
Trainer Note
Approximate stresses on the windmill are given in the handout
titled "Rules of Thumb for Wind Waterpumps"
Step 6: 25 minutes
Test more materials for strength and flexibility.
RESOURCES: Copies of Attachment 7-A
Attachment 7-A
Material Strengths & Testing
RULES OF THUMB FOR WIND WATERPUMPS
Centrifugal Force - (assuming a rotor tip speed ratio of
approximately 1)
1 pound at one foot from the hub exerts with a force of 55
pounds in a 60 mph wind.
1 kilogram at 1 meter from the hub exerts with a force of 180
kilograms in a 100 km. per hour wind.
Maximum Windmill Drag Approximation - (in a 60+ mph (100+
km. per hour) wind)
10 pounds per square foot
45 kilograms per square meter
Power Calculation -
One horsepower is equal to lifting 400 gallons of water to a
height of 10 feet in one minute.
One horsepower is equal to lifting 1500 liters of water to a
height of 3 meters in one minute.
This formula is for theoretical horsepower and does not include
the efficiency (or inefficiency) of the pump or the hydraulic friction losses in
the pipe or the mechanical friction. For real life, use about one quarter of
these figures for single acting pumps, and one half of these figures for double
acting pumps.
Pumping Capacity
A 2" pump puts out a quart for every 18 inches of stroke
A 2"
x 2" square pump puts out a quart in 14" of stroke
A 3" pump puts out a quart
for every 8 inches of stroke
A 5 cm. pump puts out a liter for every 50 cm. of stroke
A 5
cm. x 5 cm. pump puts out a liter each 40 em. of stroke
A 8 cm. pump puts out
a liter for every 20 cm. of
stroke
