OVERSHOT WATERWHEEL
A DESIGN AND CONSTRUCTION
MANUAL
Published by
VITA
1600 Wilson Boulevard, Suite 500
Arlington, Virginia 22209 USA
Tel: 703-276-1800 . Fax: 703/243-1865
Internet: pr-info@vita.org
ISBN 0-86619-067-8
[C] 1980 Volunteers in Technical Assistance
OVERSHOT WATERWHEEL
A DESIGN AND CONSTRUCTION MANUAL
I. WHAT IT IS AND
WHAT IT IS USED FOR
II. DECISION FACTORS
Applications
Advantages
Considerations
Cost Estimate
III. MAKING THE DECISION AND FOLLOWING THROUGH
IV. PRE-CONSTRUCTION CONSIDERATIONS
Undershot
Waterwheel
Overshot
Waterwheel
Site Selection
Power Output
Applications
Records
Materials and Tools
V. CONSTRUCTION
Prepare the
Diameter Section
Prepare the
Shrouds
Prepare the
Buckets
Make the Wood
Bearings
Size of the
Bearings
Attach Metal or
Wood Shaft to The Wheel
Constructing
Mountings and Tail Race
Mounting the
Wheel
Mounting the
Wheel--Vehicle Axle (Optional)
Water Delivery to
the Wheel
Maintenance
VI. DICTIONARY OF
TERMS
VII. FURTHER INFORMATION RESOURCES
VIII. CONVERSION TABLES
APPENDIX I. Site Analysis
APPENDIX II. Small Dam Construction
APPENDIX III. Pump Selection
APPENDIX IV. Calculating Bearing and Shaft Sizes
APPENDIX V. Decision Making Worksheet
APPENDIX VI. Record Keeping Worksheet
OVERSHOT WATERWHEEL
A DESIGN AND CONSTRUCTION MANUAL
I. WHAT IT IS AND WHAT IT IS USED FOR
BACKGROUND
Improved use of water as a power source has potential for
much
of the developing world.
There are few places where water is
not available in quantities sufficient for power generation.
Almost any flowing water--river, brook, or outlet of a lake
or
pona--can be put to work and will provide a steady source of
energy. Fluctuations
in the rate of flow usually are not too
large and are spread out over time; water flow is far less
subject to quick changes in energy potential and is
available
24 hours a day.
The uses of energy from water are about the same as those
for
energy from the wind--electrical generation and mechanical
power. Water-powered
turbines attached to generators are used
to generate electricity; waterwheels are generally used to
power mechanical devices such as saws and machines for
grinding
grain.
Development of water power can be advantageous in
communities
where the cost of fossil fuels is high and access to
electric
transmission lines is limited.
POSSIBLE APPLICATIONS
The cost of employing water power can be high. As with any
energy project, you must consider carefully all
options. The
potential for power generation of the water source must be
carefully matched with what it will power.
For example, if a
windmill and a waterwheel can be constructed to fill the
same
end use, the windmill may well require less time and
money. On
the other hand, it may be less reliable.
Using water power requires: 1) a constant and steady flow of
water, and 2) sufficient "head" to run the
waterwheel or turbine,
if such is being used.
"Head" is the distance the water
falls before hitting the machine, be it waterwheel, turbine,
or
whatever. A higher
head means more potential energy.
There is a greater amount of potential energy in a larger
volume
of water than in a smaller volume of water.
The concepts of
head and flow are important: some applications require a
high
head and less flow; some require a low head but a greater
flow.
Many water power projects require building a dam to ensure
both
constant flow and sufficient head.
It is not necessary to be an
engineer to build a dam. There are many types of dams, some
quite easy to build.
But any dam causes changes in the stream
and its surroundings, so it is best to consult someone
having
appropriate expertise in construction technique.
It is important to keep in mind that there can be
substantial
variation in the available flow of water, even with a dam to
store the water.
This is especially true in areas with seasonal
rainfall and cyclical dry periods.
Fortunately, in most areas
these patterns are familiar.
Waterwheels have particularly high potential in areas where
fluctuations in water flow are large and speed regulation is
not practical. In
such situations, waterwheels can be used to
drive machinery which can take large fluctuations in
rotation
and speed.
Waterwheels operate between 2 and 12 revolutions per
minute and usually require gearing and belting (with related
friction loss) to run most machines. (They are most useful
for
slow-speed) applications, e.g., flour
mills, agricultural
machinery, and some pumping
operations.
A waterwheel, because of its rugged design, requires less
care
than a water turbine.
It is self-cleaning, and therefore does
not need to be protected from debris (leaves, grass, and
stones).
Capital and labor costs can vary greatly with the way the
power
is used. For
example, an undershot waterwheel in a small stream
can be fairly easy and inexpensive to build.
On the other hand,
the set-up for generating electricity with a turbine can be
complicated and costly.
However, once a water power device is
built and in operation, maintenance is simple and low in
cost:
it consists mainly of lubricating the machinery and keeping
the
dam in good condition.
A well built and well situated water
power installation can be expected to last for 20-25 years,
given good maintenance and barring major catastrophes.
This
long life is certainly a factor to be figured into any cost
calculation.
II. DECISION FACTORS
Applications: *
water pumping.
*
Low-speed machinery applications such as
grist mills, oil presses, grinding
machines, coffee hullers, threshers, water
pumps, sugar cane presses, etc.
Advantages: * Can
work over a range of water flow and
head conditions.
*
Very simple to build and operate.
*
Virtually no maintenance required.
Considerations: * Not advisable for electrical generation or
high-speed machinery applications.
* For
optimum life expectancy water-resistant
paints are needed.
COST ESTIMATE(*)
$100 to $300 (US, 1979) including materials and labor.
-------------
(*) Cost estimates serve only as a guide and will vary from
country to country.
III. MAKING THE DECISION AND FOLLOWING THROUGH
When determining whether a project is worth the time,
effort,
and expense involved, consider social, cultural, and
environmental
factors as well as economic ones.
What is the purpose of
the effort? Who will benefit most? What will the
consequences
be if the effort is successful? And if it fails?
Having made an informed technology choice, it is important
to
keep good records. It is helpful from the beginning to keep
data on needs, site selection, resource availability,
construction progress, labor and materials costs, test
findings, etc. The information may prove an important
reference
if existing plans and methods need to be altered.
It can be
helpful in pinpointing "what went wrong?" And, of
course, it is
important to share data with other people.
The technologies presented in this and the other manuals in
the
energy series have been tested carefully, and are actually
used
in many parts of the world.
However, extensive and controlled
field tests have not been conducted for many of them, even
some
of the most common ones.
Even though we know that these
technologies work well in some situations, it is important
to
gather specific information on why they perform properly in
one
place and not in another.
Well documented models of field activities provide important
information for the development worker.
It is obviously
important for a development worker in Colombia to have the
technical design for a machine built and used in
Senegal. But
it is even more important to have a full narrative about the
machine that provides details on materials, labor, design
changes, and so forth.
This model can provide a useful frame of
reference.
A reliable bank of such field information is now
growing. It
exists to help spread the word about these and other
technologies, lessening the dependence of the developing
world
on expensive and finite energy resources.
A practical record keeping format can be found in Appendix
VI.
IV. PRE-CONSTRUCTION CONSIDERATIONS
The two most common types of waterwheels are the undershot
and
the overshot versions.
UNDERSHOT WATERWHEEL
The undershot waterwheel (see Figure 1) should be used with
a
owdfg1x9.gif (600x600)
head of 1.5 to 10 ft and flow rates from 10 to 100 cu ft per
second. Wheel
diameter should be three to four times the head
ana is usually between 6 and 20 ft.
Rotational speeds of the
wheel are from 2-12 revolutions per minute; smaller wheels
produce higher speeds.
The wheel dips from 1-3 ft into the
water. Efficiency is
in the range of 60-75 percent.
OVERSHOT WATERWHEEL
The overshot waterwheel (see Figure 2) is used with heads of
owd2x10.gif (600x600)
10-30 ft and flow rates from 1-30 cu ft per second.
Water is
guided to the wheel through a wood or metal flume.
A gate at
the end of the flume controls the water flow to the wheel.
Wheel width can be fixed depending upon the amount of water
available and the output needed.
In addition, the width of the
waterwheel must exceed the width of the flume by about 15cm
(6") because the water expands as it leaves the
flume. The
efficiency of a well constructed overshot waterwheel can be
60-80 percent.
Overshot wheels are simple to construct, but they are large
and
they require a lot of time and material--as well as a
sizeable
workspace. Before
beginning construction, it is a good idea to
be sure facilities are or will be available for transporting
the wheel and lifting it into place.
Even though an overshot wheel is simple to construct and
does
not require extreme care in cutting and fitting, it must be
strong and sturdy.
Its size alone makes it heavy, and in addition
to its own weight, a wheel must support the weight of the
water. The high
torque delivered by the wheel requires a strong
axle--a wooden beam or (depending on the size of the wheel)
a
car or tractor axle.
Attention to these points will help prevent
problems with maintenance.
Large waterwheels may be made much like a wagon wheel--with
a
rim attached to spokes.
A smaller wheel may be made of a solid
disc of wood or steel.
Construction of a wheel involves the
assembly of four basic parts: the disc or spokes of the
wheel
itself, the shrouds or sides of the buckets that hold the
water, the buckets, and the mounting framework.
Other parts are
determined by the work the wheel is intended to do and may
include a drive for a pump or grinding stone or a system of
gears and pulleys for generating electricity.
Before a wheel is constructed, careful consideration should
be
given to the site of the wheel and the amount of water
available.
Because overshot wheels work by gravity, a relatively
small flow of water is all that is needed for operation.
Even
so, this small flow must be directed into a flume or chute.
Doing this often requires construction of a small dam.
The overshot waterwheel derives its name from the manner in
which it is activated by the water.
From a flume mounted above
the wheel, water pours into buckets attached to the edge of
the
wheel and is discharged at the bottom.
An overshot wheel operates
by gravity: the water-filled buckets on the downward side
of the wheel over-balance the empty buckets on the opposite
side and keep the wheel moving slowly.
In general, overshot waterwheels are relatively efficient
mechanically and are easily maintained.
Their slow speed and
high torque make them a good choice to operate such
machinery
as grist mills, coffee hullers, and certain water
pumps. They
may even be used for generating small amounts of
electricity.
Electrical generators require a series of speed multiplying
devices that also multiply the problems of cost,
construction,
and maintenance.
Such a wheel should be located near, but not in, a stream or
river. If a site on
dry ground is chosen, the foundation may be
constructed dry and the water led to the wheel and a
tailrace
excavated (see Figure 3).
Efficiency of the wheel depends on
owd3x12.gif (600x600)
efficient and practical design considerations.
The wheel must
use the weight of the water through as much of the head as
possible. The
buckets should not spill or sling water until
very near the tailwater.
The experience of the people at an isolated hospital in
rural
Malawi serves to illustrate many of the questions, both
technical
and cultural, that go into the development of a water
power unit.
A failed cassava crop in the area led to the substitution of
a
new dietary staple--corn (maize). But the nearest mill for
grinding the corn was a 49-kilometer (30-mile) walk away.
Clearly something needed to be done to make milling
facilities
more accessible to the people.
A diesel-powered mill was too expensive and too difficult to
maintain in that remote region. The river flowing past the
hospital
seemed to hold the promise of a power source, but, again,
commercial water turbines proved too costly. Some kind of
waterwheel seemed to provide an appropriate choice.
Development of the water power site involved the combined
efforts of VITA and five VITA Volunteers, a missionary
engineer
in another area of Malawi, and OXFAM, another international
development agency. Some data was also supplied by
commercial
milling firms. Much of the labor was volunteered by local
people.
Correspondence between and among the participants involved
choice of type of wheel, determining how to provide enough
head
to develop enough power to do the job, construction of the
wheel, and selecting the proper burrs or grindstones.
Both VITA and OXFAM strongly recommended an overshot wheel
for
the reasons cited earlier: ease of construction and
maintenance,
reliability, and mechanical efficiency. With this comparison
as a guide, the overshot wheel was chosen.
Power to run the grain mill required a head of about 427cm
(14
ft, which would accommodate a wheel nearly 361cm (12 ft)
across. The higher head necessary for the overshot wheel
made
it necessary to clear away additional boulders from the
river
bed, but this original investment in labor was more than
returned by the increased efficiency of the wheel.
Additional correspondence (except for a couple of visits by
the
missionary engineer, the entire problem-solving process was
handled by mail!) determined the precise shape, angle, size,
and numbers of the buckets on the wheel. Also necessary was
the
design of a system of pulleys to transfer the power of the
wheel to the milling operation.
As the wheel was constructed, attention was given to the
grindstones.
Granite found in the area seemed ideal, but proved to
be too difficult for local stone cutters to deal with and
yet
not durable enough to be worth the time. Advice was sought
from
a millwright in New York and a variety of commercial milling
firms. Ultimately a small commercial mill was chosen, with
continued
study going into preparing traditional stones.
In one of the last letters, hospital staff related that the
wheel and mill were in place and operating. And from
experience
gained in this project they were already considering the
possibility
of constructing turbines to generate electricity.
SITE SELECTION
A careful analysis of the proposed site of the waterwheel is
an
important early step before construction begins. Whether it
is
a good idea to try to harness a stream depends on the
reliability
and quantity of the flow of water, the purpose for which
power is desired, and the costs involved in the effort. It
is
necessary to look at all factors carefully. Does the stream
flow all year round--even during dry seasons? How much water
is
available at the driest times? What will the power do--grind
grain, generate electricity, pump water? These questions and
others must be asked.
If a stream does not include a natural waterfall of
sufficient
height, a dam will have to be built to create the 'head'
necessary
to run the wheel. Head is the vertical distance which the
water falls.
The site of the dam and wheel will affect the amount of head
available. Water power can be very economical when a dam can
be
built into a small river with a relatively short (less than
100
ft) conduit (penstock for conducting water to the
waterwheel).
Development costs can be fairly high when such a dam and
pipeline can provide a head of only 305cm (10 ft) or less.
While a dam is not required if there is enough water to
cover
the intake of a pipe or channel at the head of the stream
where
the dam would be placed, a dam is often necessary to direct
the
water into the channel intake or to get a higher head than
the
stream naturally affords. This, of course, increases expense
and time and serves as a very strong factor in determining
the
suitability of one site over another.
A thorough site analysis should include collection of the
following data:
* Minimum flow in
cubic feet or cubic meters per second.
* Maximum flow to be
utilized.
* Available head in
feet or meters.
* Site sketch with
elevations, or topographic map with site
sketched in.
* Water condition,
whether clear, muddy, sandy, etc.
* Soil condition,
the velocity of the water and the size of
the ditch or
channel for carrying it to the works depends on
soil condition.
Measurements of stream flow should be taken during the
season
of lowest flow to guarantee full power at all times. Some
investigation of the stream's history should be made to
determine if there are perhaps regular cycles of drought
during
which the stream may dry up to the point of being unusable.
Appendices I and II of this manual contain detailed
instructions for measuring flow, head, etc., and for
building
penstocks and dams. Consult these sections carefully for
complete directions.
POWER OUTPUT
The amount of water available from the water source can be
determined to assist in making the decision whether to
build.
Power may be expressed in terms of horsepower or kilowatts.
One
horsepower is equal to 0.7455 kilowatts; one kilowatt is
about
one and a third horsepower. The gross power, or full amount
available from the water, is equal to the useful power plus
the
losses inherent in any power scheme. It is usually safe to
assume that the net or useful power in small power
installations
will only be half of the available gross power due to
water transmission losses and the gearing necessary to
operate
machinery.
* Gross power is
determined by the following formula:
In English units:
Gross Power
(horsepower) =
Minimum Water
Flow (cu ft/sec) X Gross Head (ft)
-------------------------------------------------
8.8
In Metric units:
Gross Power
(metric horsepower) =
1,000 Flow (cu
m/sec) X Head (m)
-----
75
* Net power
available at the turbine shaft is:
In English units:
Net Power =
Minimum Water Flow
X Net Head(*) X Turbine Efficiency
-----------------------------
8.8
In Metric Units:
Net Power =
Minimum Water
Flow X Net Head(*) X Turbine Efficiency
-----------------------------
75/1,000
APPLICATIONS
While water pumping is an obvious use for the waterwheel,
other
machinery can be adapted to use the mechanical power output
of
the wheel. Almost any stationary machine which is currently
hand-powered could be run by waterwheel power. Only in the
case
where the wheel and the machine are separated by long
distances
should there be any significant problem.
One problem which can occur when the machine is located some
distance from the wheel is that the drive shaft of the
machine
will not easily be aligned with the waterwheel shaft.
Alignment
difficulties can be overcome simply and cheaply with old
automobile
rear axle assemblies, with the gears welded or jammed to
give constant speed on both sides.
If the water supply to the wheel fluctuates, the speed of
the
wheel will vary. These speed variations are small and will
generally not be of any consequence. If the variable speeds
create problems, either a special constant velocity joint
(as
from the front wheel drive automobile) or two ordinary U
joints
must be used, each to compensate for the different motion of
the other.
--------------
(*) The net head is obtained by deducting the energy losses
from
the gross head. These losses are discussed in Appendix I.
When
it is not known, a good assumption for waterwheel efficiency
is
60 percent.
Flexible shafts are commercially available but are of
limited
torque-carrying capacity.
Solid shafts can transmit torque over considerable distance
but
require bearings for support and are expensive.
Generation of electricity is a possibility which will
probably
spring to the minds of most people reading this manual.
There
are waterwheel-driven electric generators in operation
today,
but the number of failed attempts testifies to the fact that
it
is not a simple, inexpensive project.
RECORDS
The need for power should be documented, and the
measurements
taken for the site analysis should be recorded. Costs of
construction
and operation can be compared to the benefit gained
from the device to determine its real worth. (In making
comparisons,
don't forget to include the pond or lake created by the
dam--it can be used to water livestock, raise fish, or
irrigate
fields.)
MATERIALS AND TOOLS
A simple, relatively economical 112cm (5 ft) wheel for
pumping
water can be made out of a disc of heavy plywood to which
the
buckets and shrouds are attached. Plywood is chosen because
it
is easy to use and relatively accessible; however, it does
require special treatment to avoid deterioration and, in
some
places, may be quite expensive. The shaft of the wheel can
be
made either from metal or wood: the rear axle from an
automobile
may be used but, in most cases, axles are available only
at great expense.
Lumber for shrouds, buckets, and rim reinforcement may be of
almost any type available; hardwood is preferable. Ordinary
wood saws, drills, and hammer are used in construction.
Welding
equipment is convenient if an automobile rear axle is being
used. Materials for the dam and mounting structure should be
chosen from whatever is at hand, based on the guidelines in
this manual. While materials for the wheel may vary with
what
is available, they should include:
Materials
* 2cm thick
plywood(*)--at least 112cm square.
* 6mm thick
plywood(*)--122cm X 244cm sheet.
* 703cm total length
of 3cm X 6cm boards to reinforce the edge
of the disc.
* 703cm total length
of 2cm X 30cm boards for the shrouds.
* 438cm total length
of 2cm X 30cm boards for buckets.
* 703cm total length
of 6mm X 20cm plywood* to reinforce the
outside of the
shrouds.
* 110cm long 5cm dia
solid steel shaft or 9cm sq hardwood
shaft. (Automobile
rear axle is optional.)
* 5cm dia steel hubs
(2) for steel shaft.
* 10 liters asphalt
patching compound (or tar).
* Timbers and lumber
for support structure as needed, nails,
tin cans, bolts.
-------------
(*) Marine-grade plywood is preferred; waterproofed
exterior-grade
can be used.
Tools
* Protractor
* Wood saw
* Wood drill/bits
* Hammer
* Welding equipment
(optional)
V. CONSTRUCTION
PREPARE THE DIAMETER SECTION
* Make a disc out of
the 2cm thick plywood 112cm in dia. This
is done using the
meter stick.
* Nail one end of
the ruler to the center of the plywood
sheet.
* Measure 56cm from
the nail and attach a pencil to the ruler.
* Scribe a circle
and cut out disc with a wood saw (see Figure 4
owd4x21.gif (256x256)
below).
* Divide the circle
in half and then into quarters using a
pencil and
straight edge.
* Divide each
quarter into thirds (30[degrees] intervals on protractor).
The finished disc
should look like Figure 5. The
owd5x22.gif (313x253)
twelve reference
lines will be used to guide the positioning
of the buckets.
* Take 25-40cm
lengths of 2cm X 3cm X 6cm lumber and nail them
around the outside
diameter of the wood disc on both sides
so that the outer
edge projects slightly beyond the rim of
the disc (see
Figure 6).
owd6x23.gif (600x600)
* Cut the 6mm thick
X 122cm X 244cm plywood sheets into six
strips 40.6cm wide
X 122cm long.
* Bend and nail
three of the strips around the disc so that
they overhang
equally on both sides.
* Bend and nail a
second layer over the first, staggering the
joints so as to
give added strength and tightness (see
Figure 7). These
layers form what is called the sole plate
owd7x24.gif (600x600)
or backside of the
buckets which will be attached later.
PREPARE THE SHROUDS
* Cut the shrouds,
or sides, of the buckets from 2cm X 30cm
wide boards. Nail
one end of the meter stick to a piece of
lumber. Measure
57.2cm from this nail. Drill 6mm hole and
attach a pencil.
* Measure 20.5cm
from this
pencil, drill 6mm
hole and
attach another
pencil. This
becomes a compass
for making
the shrouds (see
Figure 8).
owd8x24.gif (600x600)
* Take 2cm X 30cm
boards and
scribe the outline
of the
shroud on, the
wood. Cut out
enough of the
shrouds to fit
around both sides
of the disc.
Shroud edges will
have to be
planed to fit.
* Nail the shroud
pieces flush to the edge of the sole plate
from the back side
of the sole plate.
* Use the
"compass" trace and cut out a second set of shrouds,
or shroud covers,
from 6mm thick plywood.
* Nail the plywood
shroud covers on the outside of the first
shrouds, with the
joints overlapped (see Figure 9). Be sure
owd9x25.gif (600x600)
that the bottom
edge of this second set of shrouds is flush
with the bottom
edge of the first layer of the sole plate.
* Fill in any cracks
and seams
with the asphalt
patching
compound or
waterproof sealer.
The finished wheel
will look
something like a
cable spool
(see Figure 10).
owd10x25.gif (486x486)
PREPARE THE BUCKETS
* Make the front
sides of the twelve (12) buckets from
hardwood boards
2cm X 30cm. The width of the front board
will be 36.5cm.
* Make the bottom
sections of the buckets from hardwood boards
2cm X 8cm. The
length of each board will be 36.5cm.
* Cut the bottom of
each 30cm section at a 24[degrees] angle from the
horizontal and the
top edge at a 45[degrees] angle from the horizontal
as shown in Figure
11 before putting the two sections
owd11x26.gif (437x437)
together.
* Nail the buckets
together (see Figure 12). Each bucket
owd12x26.gif (486x486)
should have an
inside angle of 114[degrees].
Place each bucket between the shrouds. Using the reference
lines scribed on the disc earlier, match one bucket to each
line as shown in Figure 13. The buckets can then be nailed
owd13x27.gif (600x600)
in place.
* Fill in all
cracks with the asphalt patching compound.
MAKE THE WOOD BEARINGS
Bearings, for attaching the shaft to the wheel, will last
longer if they are made from the hardest wood available
locally.
Generally, hardwoods are heavy and difficult to work. A
local wood-craftsman should be able to provide information
on
the hardest woods. If there is doubt concerning the hardness
or
the self-lubricating quality of the wood that is going to be
used in the bearings, thoroughly soaking the wood with oil
will
give longer life to the bearings.
Some advantages in using oil-soaked bearings are that they:
* Can be made from
locally available materials.
* Can be made by
local people with wood-working skills.
* Are easily
assembled.
* Do not require
further lubrication or maintenance in most
cases.
* Are easily
inspected and adjusted for wear.
* Can be repaired or
replaced.
* Can provide a
temporary solution to the repair of a more
sophisticated
production bearing.
The oiliness of the wood is important if the bearing is not
going to be lubricated. Woods having good self-lubricating
properties
often are those which:
* Are easily
polished.
* Do not react with
acids (e.g., teak).
* Are difficult to
impregnate with preservatives.
* Cannot be glued
easily.
Usually the hardest wood is found in the main trunk just below
the first branch. Wood freshly cut should be allowed to dry
for
two to three months to reduce moisture content. High
moisture
content will result in a reduction in hardness and will
cause
greater wear.
SIZE OF THE BEARING
The length of the wood bearings should be at least twice the
shaft diameter. For example, for the 5cm dia axle or shaft
of
the waterwheel presented here, the bearing should be at
least
10cm long. The thickness of the bearing material at any
point
should be at least the shaft diameter (i.e., for a 5cm dia
shaft a block of wood 15cm X 15cm X 10cm long should be
used).
Split block bearings (see Figure 14) should be used for the
owd14x29.gif (486x486)
waterwheel because it is a heavy piece of equipment and can
cause a great deal of wear. These bearings are simple to
make
and replace.
The following steps outline the construction of a
split-block
bearing:
* Saw timber into an
oblong block slightly larger than the
finished bearing
to allow for shrinkage.
* Bore a hole
through the wood block the size of the axle/
shaft diameter.
* Cut block in half
and clamp firmly together for drilling.
* Drill four 13mm or
larger holes for attaching bearing to
bearing
foundation. After drilling, the two halves should be
tied together to
keep them in pairs.
* Impregnate the
blocks with oil.
* Use an old
20-liter (5-gal) drum filled two-thirds full with
used engine oil or
vegetable oil.
* Place wood blocks
in oil and keep them submerged by placing
a brick on top
(see Figure 15).
owd15x30.gif (486x486)
* Heat the oil until
the moisture
in the wood is
turned
into steam--this
will give
the oil an
appearance of
boiling rapidly.
* Maintain the heat
until
there are only
single
streams of small
pin-sized
bubbles rising to
the oil's
surface (see
Figure 16).
owd16x31.gif (486x486)
This may take 30
minutes to
2 hours, or
longer, depending
on the moisture
content
of the wood.
Soon after heating
the bearing
blocks in oil,
many surface
bubbles one-inch
in
diameter, made
from a multitude
of smaller
bubbles, will
appear on the
surface.
As the moisture
content of
blocks is reduced,
the surface
bubbles will
become
smaller in size.
When the surface
bubbles are
formed from single
streams of
pin-sized bubbles,
stop
heating.
* Remove the heat
source and leave the blocks in the oil to
cool overnight.
During this time the wood will absorb the
oil.
BE VERY CAREFUL IN HANDLING THE CONTAINER OF HOT OIL.
* Remove wood blocks
from the oil, reclamp and rebore the
holes as necessary to compensate for
shrinkage that may have
taken place. The
bearings are now ready to be used.
(Calculations for shaft and bearing sizes for larger
waterwheels
are provided in Appendix IV.)
ATTACH METAL OR WOOD SHAFT TO WHEEL
Metal Shaft
* Drill or cut out a
5cm dia round hole in the center of the
wheel.
* Attach 5cm dia
steel hubs as shown in Figure 17 using four
owd17x32.gif (486x486)
20mm X 15cm long
bolts.
* Insert 110cm long
metal shaft through the wheel center so
that the shaft
extends 30cm from one edge of the shroud and
38.2cm from the
other edge (see Figure 18).
owd18x32.gif (486x486)
* Weld the shaft to
the hub
assembly on both
sides as
shown in Figure
19.
owd19x32.gif (486x486)
Wood Shaft
* Drill and
carefully cut out a 9cm square hole in the center
of the wheel.
* Measure 49cm from
one end of the 110-cm long wood shaft and
mark with a
pencil. Measure 59cm from other end of the shaft
and do the same.
Turn the shaft over and repeat the procedure.
There should be
2cm between the two marks.
* Cut grooves 3cm
wide X 1cm deep on both sides of the shaft
as shown below in
Figure 20.
owd20x33.gif (486x486)
* Cut the 9cm shaft
to 5cm dia only at the bearing (see Figure 21).
owd21x33.gif (230x437)
This step will
take some time. A tin can 5cm in
diam or the
bearing itself can be used to gauge the cutting
process. The
finished shaft must be sanded and made as round
and smooth as
possible to prevent excessive or premature
wear on the
bearing.
* Insert wood shaft
through wheel center so that the grooves
show on either side
of the wheel disc.
* Fit 3cm X 6cm X
15cm boards into the grooves so that they
fit tightly. Tack
each board to disc using nails to ensure
a tight fit in the
groove.
* Drill two 20mm dia
holes through each 3cm X 6cm boards and
disc. Insert 20mm
dia X 10cm long bolts with washer through
the disc and
attach with washer and nut (see Figure 22 and Figure 23).
owd22x34.gif (486x600)
Remove nails.
* The wheel is now
ready to be mounted.
CONSTRUCTING MOUNTINGS AND TAILRACE
Stone or concrete pillars make the best mounting for the
waterwheel. Heavy wood pilings or timber also have been used
successfully. The primary determinant is, of course, local
availability. Foundations should rest on a solid base--firm
gravel or bedrock if possible to avoid settling. Large area
footings will also help, and will prevent damage from stream
erosion. If one end of the shaft is supported at the power
plant building, this support should be as solid as the outer
pillar.
Provision should be made for periodic adjustment in the alignment
of the bearings in case one of the supports should settle
or slide. Wood blocks can be used to mount the bearings, and
these can be changed to adjust for any differences in
elevation
or placement. It is important that bearings and wheel shift
be
kept in perfect alignment at all times.
If the discharge or tailwater is not immediately removed
from
the vicinity of the wheel, the water will tend to back up on
the wheel causing a serious loss of power. However, the drop
necessary to remove this water should be kept at a minimum
in
order to lose as little as possible of the total available
head.
The distance between the bottom of the wheel and the
tailrace
should be 20-30cm (4-6"). The tailrace or discharge
channel
should be smooth and evenly shaped down the stream bed below
the wheel (see Figure 24).
owd24x35.gif (486x600)
MOUNTING THE WHEEL
Attach the bearings to the shaft and lift the wheel onto
mounting pillars. Align the wheel vertically and
horizontally
through the use of wood blocks under the bearings. Once
alignment has been done, drill through four holes in the
bearing into the wood shim and mounting pillar.
Attach the bearings to the pillars using lag/anchor bolts in
the case of concrete pillars or lag/anchor screws 13mm dia X
20cm long if wood pilings are used.
In mounting the shaft in the bearings, carefully avoid
damage
to the bearings and shaft. The shaft and bearings must be
accurately aligned and solidly secured in place before the
chute is assembled and located.
The wheel must be balanced in order to run smoothly, without
uneven wear, or excess strain on the supports. When the
wheel
is secured on the mountings, it should turn easily and come
to
a smooth, even stop. If it is unbalanced, it will swing back
and forth for a time before stopping. If this should occur,
add
a small weight (i.e., several nails or a bolt), at the top
of
the wheel when it is stopped. With care, enough weight can
be
added to balance the wheel perfectly.
MOUNTING THE WHEEL--VEHICLE AXLE (Optional)
Take a rear axle from a full-sized car and fix the
differential
gears so the two axles turn as one unit. You can jam these
gears by welding so they don't operate. Cut off one axle and
the axle housing to get rid of the brake assembly if you
wish.
The other axle should be cleaned of brake parts to expose
the
hub and flange. You may have to knock the bolts out and get
rid
of the brake drum. The wooden disc of the waterwheel needs
to
have a hole made in its center to fit the car wheel hub
closely. Also it should be drilled to match the old bolt
holes
and bolts installed with washers under the nuts.
Before mounting the wheel in place, have a base plate welded
to
the axle housing (see Figure 25). It should be on what is to
be
owd25x37.gif (600x600)
the underside, with two holes for 13mm lag screws. Make some
kind of anchor to hold the opposite housing in place.
WATER DELIVERY TO WHEEL
For highest efficiency, water must be delivered to the wheel
from a chute placed as close to the wheel as possible, and
arranged so that the water falls into the buckets just after
they reach upper dead center (see Figure 26). The relative
owd26x38.gif (600x600)
speed of the buckets and the water are very important.
The speed of the wheel will be reduced as the load it is
driving increases. When large
changes take place in the load,
it is necessary to change the amount of water or the
velocity
of its approach to the wheel. This is done by a control gate
located near the wheel, which can be raised or lowered
easily
and fixed at any position to give moderately accurate
adjustment.
The delivery chute should run directly from the control gate
to
the waterwheel, and be as short as construction will permit
(30cm-91cm long is best). A little slope is necessary to
maintain the water velocity (1% or 30cm in every 3000cm will
be
satisfactory).
Flat-bottomed chutes are preferable. Even when water is
delivered through a pipe, this should terminate in a control
box and delivery made to the wheel through an open,
flat-bottomed chute (see Figure 27). The tip of the chute
owd27x39.gif (540x540)
should be perfectly straight and level, and lined with sheet
metal to prevent wear.
The chute should not be as wide as the waterwheel. This
allows
air to escape at the ends of the wheel as water enters the
buckets. The width of the chute is usually 10-15cm
(4-6")
narrower than the width of the wheel. (In this case where
the
bucket width is 36.5cm the chute width will be 22-26cm.)
MAINTENANCE
All plywood parts must be waterproofed to keep them from
deteriorating. Other wood parts may be painted or varnished
for
a protective coating. This helps extend the life of the
wheel.
wheel. Periodic repainting may be needed. Except for the
plywood portions, the decision to paint can be made on
purely
economic grounds. If a very durable wood has been used
initially, painting is a luxury. If a somewhat less durable
species is used, painting is probably cheaper and easier
than
early replacement or repair of the wheel.
The only major maintenance problem is in bearing wear.
Generous
allowances have been made in bearing size but the bearings
will
still wear. When worn, the two halves can be interchanged;
after further wear, the life of the bearing can be extended
by
planing off a small amount of wood from the matching faces.
This will drop the wheel from its original position.
Inserting
wood or shimming under the bearing block with metal plates
will
compensate for this. Bearing replacement, when the block is
completely worn through, is a simple matter.
Generally speaking, the bearing should be lubricated as
needed. Oils/grease/vegetable oils applied periodically in
small amounts will slow the wear rate.
VI. GLOSSARY
CATASTROPHE--A great and sudden disaster of calamity.
CYCLICAL DRY PERIODS--A periodically repeated sequence of
environmental
conditions where there is a lack of
rainfall or water
supply.
DIA (DIAMETER)--A straight line passing through the center
of a
circle and
meeting at each end of the circumference.
EMBED--To fix firmly in a surrounding mass.
Head--Measurement of the difference in depth of a liquid at
two
given points (see Appendix I).
FLUME--A channel or chute for directing the flow of water.
FLUCTUATIONS--Irregular variations or instability of a
regular
process.
GRAVITY--The force of attraction that causes terrestial
bodies
to tend to
fall toward the center of the earth.
RACK AND PINION--A device to
owddrx41.gif (230x437)
convert rotary
motion to
linear motion.
SHROUD--A device that covers, conceals, or protects
something.
SLUICE--A man-made water channel with a valve or gate to
regulate the flow.
SPROCKETS--Any of various toothlike projections arranged on
a
wheel rim to
engage the links of a chain.
TELESCOPIC--Capable of being made longer or shorter by the
sliding of
overlapping tubular sections.
TOPOGRAPHIC MAP--A map showing the configuration of a place
or
region,
usually by the use of contour lines.
VII. FURTHER INFORMATION RESOURCES
Cloudburst Press Ltd. Cloudburst manual, 1973. Cloudburst
Press
Ltd., Mayne
Island, British Columbia, VON 2JO Canada.
This manual,
written by "homesteaders" in the Pacific
Norethwest,
has about 30 pages dealing with various
aspects of
water power. It covers measuring
potential
power, dams,
and designs and construction of waterwheels.
Highly
readable and eminently practical, it is
written by
and for "do-it-yourselfers" working with
limited
resources. Also has excellent
illustrations.
Hamm, Hans W. Low Cost Develoment of Small Water Power
Sites,
1967. VITA,
3706 Rhode Island Avenue, Mount Rainier,
Maryland
20822 USA. Written expressly to be used in
developing
areas, this manual contains basic information
on measuring
water power potential, building small
dams,
different types of turbines and waterwheels, and
several
necessary matehmatical tables. Also has
some
information
on manufactured turbines available. A
very
useful book.
Monson, O.W., and Hill, Armin J. Overshot and Current Water
Wheels,
January 1942. Bulletin 398, Montana State
College
Agricultural and Experimental Station, Bozeman,
Montana,
USA. Written for the use of farmers and
ranchers,
this bulletin
tells how to build "homemade" waterwheels
from wood and
scrap metal, as the emphasis is on
simplicity
and low cost. A good guide for building
and
installing
overshot and undershot waterwheels, it is
profusely
illustrated and contains many practical hints
for consideration.
Ovens, William G. A Design Manual for Waterwheels, 1975.
VITA,
3706 Rhode
Island Avenue, Mount Rainier, Maryland 20822
USA.
The basic manual for waterwheel design and
construction. Includes both
theoretical and practical
considerations, and is written to be used by people
with a
limited technical understanding. Also
has a
section on
waterwheel applications as well as 16 highly
useful tables
and several schematic diagrams.
VIII. CONVERSION TABLES
UNITS OF LENGTH
1 Mile
= 1760 Yards =
5280 Feet
1 Kilometer
= 1000 Meters =
0.6214 Mile
1 Mile
= 1.607 Kilometers
1 Foot
= 0.3048 Meter
1 Meter
= 3.2808 Feet =
39.37 Inches
I Inch
= 2.54 Centimeters
1 Centimeter
= 0.3937 Inches
UNITS OF AREA
1 Square Mile
= 640 Acres =
2.5899 Square Kilometers
1 Square Kilometer
= 1,000,000 Square Meters =
0.3861 Square Mile
1 Acre
= 43,560 Square Feet
1 Square Foot
= 144 Square Inches =
0.0929 Square Meter
1 Square Inch
= 6.452 Square Centimeters
1 Square Meter
= 10.764 Square Feet
1 Square Centimeter
= 0.155 Square Inch
UNITS OF VOLUME
1.0 Cubic Foot
= 1728 Cubic Inches =
7.48 US Gallons
1.0 British Imperial
Gallon
= 1.2 US Gallons
1.0 Cubic Meter
= 35.314 Cubic Feet =
264.2 US Gallons
1.0 Liter
= 1000 Cubic Centimeters =
0.2642 US Gallons
1.0 Metric Ton
= 1000 Kilograms =
2204.6 Pounds
1.0 Kilogram
= 1000 Grams =
2.2046 Pounds
1.0 Short Ton
= 2000 Pounds
UNITS OF PRESSURE
1.0 Pound per square inch
= 144 Pound per square foot
1.0 Pound per square inch
= 27.7 Inches of water*
1.0 Pound per square inch
= 2.31 Feet of water*
1.0 Pound per square inch
= 2.042 Inches of mercury*
1.0 Atmosphere
= 14.7 Pounds per square inch (PSI)
1.0 Atmosphere
= 33.95 Feet of water*
1.0 Foot of water = 0.433 PSI
= 62.355 Pounds per square foot
1.0 Kilogram per square centimeter
= 14.223 Pounds per square inch
1.0 Pound per square inch
= 0.0703 Kilogram per square
centimeter
UNITS OF POWER
1.0 Horsepower (English)
= 746 Watt = 0.746 Kilowatt (KW)
1.0 Horsepower (English)
= 550 Foot pounds per second
1.0 Horsepower (English)
= 33,000 Foot pounds per minute
1.0 Kilowatt (KW) = 1000 Watt
= 1.34 Horsepoer (HP) English
1.0 Horsepower (English)
= 1.0139 Metric horsepower
(cheval-vapeur)
1.0 Metric horsepower
= 75 Meter X Kilogram/Second
1.0 Metric horsepower
= 0.736 Kilowatt
= 736 Watt
-----------------
(*) At 62 degrees Fahrenheit (16.6 degrees Celsius).
APPENDIX I
SITE ANALYSIS
This Appendix provides a guide to making the necessary
calculations
for a detailed site analysis.
Data Sheet
Measuring Gross Head
Measuring Flow
Measuring Head Losses
DATA SHEET
1. Minimum flow of
water available in cubic feet
per second (or
cubic meters per second).
-----
2. Maximum flow of
water available in cubic feet
per second (or
cubic meters per second).
-----
3. Head or fall of
water in feet (or meters).
-----
4. Length of pipe
line in feet (or meters) needed
to get the
required head.
-----
5. Describe water
condition (clear, muddy, sandy,
acid).
-----
6. Describe soil
condition (see Table 2).
-----
7. Minimum tailwater
elevation in feet (or meters).
-----
8. Approximate area
of pond above dam in acres (or
square
kilometers).
-----
9. Approximate depth
of the pond in feet (or
meters).
-----
10. Distance from power plant to where electricity
will be used in
feet (or meters).
-----
11. Approximate distance from dam to power plant.
-----
12. Minimum air temperature.
-----
13. Maximum air temperature.
-----
14. Estimate power to be used.
-----
15. ATTACH SITE SKETCH WITH ELEVATIONS, OR TOPOGRAPHIC
MAP WITH SITE
SKETCHED IN.
The following questions cover information which, although
not
necessary in starting to plan a water power site, will
usually
be needed later. If
it can possibly be given early in the project,
this will save time later.
1. Give the type,
power and speed of the machinery to be
driven and
indicate whether direct, belt, or gear drive is
desired or
acceptable.
2. For electric
current, indicate whether direct current is
acceptable or
alternating current is required. Give
the
desired voltage,
number of phases and frequency.
3. Say whether
manual flow regulation can be used (with DC
and very small
AC plants) or if regulation by an automatic
governor is
needed.
MEASURING GROSS HEAD
Method No. 1
1. Equipment <see figure 1>
owdd1x51.gif (317x317)
a. Surveyor's
leveling instrument--consists of a spirit
level fastened
parallel to a telescopic sight.
b. Scale--use wooden
board approximately 12 ft in length.
2. Procedure <see figure 2>
owdd2x52.gif (600x600)
a. Surveyor's
level on a tripod is placed downstream from
the power
reservoir dam on which the headwater level is
marked.
b. After taking a
reading, the level is turned 180[degrees] in a
horizontal
circle. The scale is placed downstream
from it
at a suitable
distance and a second reading is taken.
This process is
repeated until the tailwater level is
reached.
Method No. 2
This method is fully reliable, but is more tedious than
Method
No. 1 and need only be used when a surveyor's level is not
available.
1. Equipment <see figure 3>
owdd3x52.gif (353x353)
a. Scale
b. Board and
wooden plug
c. Ordinary
carpenter's level
2. Procedure <see figure 4>
owdd4x53.gif (600x600)
a. Place board
horizontally at headwater level and place
level on top of
it for accurate leveling. At the downstream
end of the
horizontal board, the distance to a
wooden peg set
into the ground is measured with a scale.
b. The process is
repeated step by step until the tailwater
level is
reached.
MEASURING FLOW
Flow measurements should take place at the season of lowest
flow in order to guarantee full power at all times.
Investigate
the stream's flow history to determine the level of flow at
both maximum and minimum. Often planners overlook the fact
that
the flow in one stream may be reduced below the minimum
level
required. Other streams or sources of power would then offer
a
better solution.
Method No. 1
For streams with a capacity of less than one cubic foot per
second, build a temporary dam in the stream, or use a
"swimming
hole" created by a natural dam. Channel the water into
a pipe
and catch it in a bucket of known capacity. Determine the
stream flow by measuring the time it takes to fill the
bucket.
Stream flow (cubic
ft/sec) = Volume of bucket (cubic ft)
----------------------------
Filling time (seconds)
Method No. 2
For streams with a capacity of more than 1 cu ft per second,
the weir method can be used. The weir is made from boards,
logs, or scrap lumber. Cut a rectangular opening in the
center. Seal the seams of the boards and the sides built
into
the banks with clay or sod to prevent leakage. Saw the edges
of
the opening on a slant to produce sharp edges ont he
upstream
side. A small pond is formed upstream from the weir. When
there
is no leakage and all water is flowing through the weir
opening, (1) place a board across the stream and (2) place
another narrow board at right angles to the first, as shown
below.
owdd5x55.gif (600x600)
Use a carpenter's level to be sure the second board is
level.
Measure the depth of the water above the bottom edge of the
weir with the help of a stick on which a scale has been
marked. <see figure 5> Determine the flow from Table 1
on page 56.
owdd6x55.gif (393x393)
Table I
FLOW VALUE (Cubic Feet/Second)
Weir Width
Overflow Height 3
feet 4 feet
5 feet 6 feet
7 feet
8 feet 9 feet
1.0
inch
0.24 0.32
0.40
0.48 0.56
0.64
0.72
2.0
inches
0.67 0.89
1.06
1.34 1.56
1.80
2.00
4.0
inches
1.90 2.50
3.20
3.80 4.50
5.00
5.70
6.0
inches
3.50 4.70
5.90
7.00 8.20
9.40
10.50
8.0
inches
5.40 7.30
9.00
10.80 12.40
14.60
16.20
10.0
inches
7.60 10.00
12.70
15.20 17.70
20.00
22.80
12.0
inches
10.00 13.30
16.70
20.00 23.30
26.60
30.00
Method No. 3
The float method is used for larger streams. <see figure
6> Although it is not
owdd7x56.gif (600x600)
as accurate as the previous two methods, it is adequate for
practical purposes. Choose a point in the stream where the
bed
is smooth and the cross section is fairly uniform for a
length
of at least 30 ft. Measure water velocity by throwing pieces
of
wood into the water and measuring the time of travel between
two fixed points, 30 ft or more apart. Erect posts on each
bank
at these points. Connect the two upstream posts by a level
wire
rope (use a carpenter's level). Follow the same procedure
with
the downstream posts. Divide the stream into equal sections
along the wires and measure the water depth for each
section.
In this way, the cross-sectional area of the stream is
determined.
use the following formula to calculate the flow:
Stream Flow (cu
ft/sec) = Average cross-sectional flow area
(sq ft) X velocity (ft/sec)
MEASURING HEAD LOSSES
"Net Power" is a function of the "Net
Head." The "Net Head" is
the "Gross Head" less the "Head Losses."
The illustration below
shows a typical small water power installation. The head
losses
are the open-channel losses plus the friction loss from flow
through the penstock. <see figure 7>
owdd8x57.gif (600x600)
A TYPICAL
INSTALLATION FOR A LOW-OUTPUT WATER POWER PLANT
1.
River
2.
Dam with Spillway
3.
Intake to Headrace
4.
Headrace
5.
Intake to Turbine Penstock
6.
Trashrack
7.
Overflow of Headrace
8.
Penstock
9.
Turbine Inlet Valve
10.
Water Turbine
11.
Electric Generator
12.
Tailrace
Open Channel Bead Losses
The headrace and the tailrace in the illustration above are
open channels for transporting water at low velocities. The
walls of channels made of timber, masonry, concrete, or
rock,
should be perpendicular. Design them so that the water level
height is one-half of the width. Earth walls should be built
at
a 45[degrees] angle. Design them so that the water level
height is
one-half of the channel width at the bottom. At the water
level
the width is twice that of the bottom. <see figure 8>
owdd9x58.gif (600x600)
The head loss in open channels is given in the nomograph.
The
friction effect of the material of construction is called
"N".
Various values of "N" and the maximum water
velocity, below
which the walls of a channel will not erode are given.
TABLE II
Maximum Allowable
Water Velocity
Material of Channel Wall
(feet/second)
Value of "n"
Fine grained sand
0.6
0.030
Course sand
1.2
0.030
Small stones
2.4
0.030
Coarse stones
4.0
0.030
Rock
25.0
(Smooth)
0.033 (Jagged) 0.045
Concrete with sandy water
10.0
0.016
Concrete with clean water
20.0
0.016
Sandy loam, 40% clay
1.8
0.030
Loamy soil, 65% clay
3.0
0.030
Clay loam, 85% clay
4.8
0.030
Soil loam, 95% clay
6.2
0.030
100% clay
7.3
0.030
Wood
0.015
Earth bottom with rubble sides
0.033
The hydraulic radius is equal to a quarter of the channel
width, except for earth-walled channels where it is 0.31
times
the width at the bottom.
To use the nomograph, a straight line is drawn from the
value
of "n" through the flow velocity to the reference
line. The
point on the reference line is connected to the hydraulic
radius and this line is extended to the head-loss scale
which
also determines the required slope of the channel.
Using a Nomograph
After carefully determining the water power site
capabilities
in terms of water flow and head, the nomograph is used to
ngraph1.gif (600x600)
determine:
* The width/depth of
the channel needed to bring the water to
the spot/location
of the water turbine.
* The amount of head
lost in doing this.
To use the graph, draw a straight line from the value of
"n"
through the flow velocity through the reference line tending
to
the hydraulic radius scale. The hydraulic radius is
one-quarter
(0.25) or (0.31) the width of the channel that needs to be
built. In the case where "n" is 0.030, for
example, and water
flow is 1.5 cubic feet/second, the hydraulic radius is 0.5
feet
or 6 inches. If you are building a timber, concrete,
masonry,
or rock channel, the total width of the channel would be 6
inches times 0.25, or 2 feet with a depth of at least 1
foot.
If the channel is made of earth, the bottom width of the
channel
would be 6 times 0.31, or 19.5 inches, with a depth of at
least 9.75 inches and top width of 39 inches.
Suppose, however, that water flow is 4 cubic feet/second.
Using
the graph, <see graph> the optimum hydraulic radius
would be approximately
ngraph2.gif (600x600)
2 feet--or for a wood channel, a width of 8 feet. Building a
wood channel of this dimension would be prohibitively
expensive.
However, a smaller channel can be built by sacrificing some
water head. For example, you could build a channel with a
hydraulic radius of 0.5 feet or 6 inches. To determine the
amount of head that will be lost, draw a straight line from
the
value of "n" through the flow velocity of 4
[feet.sup.3]/second to the
reference line. Now draw a straight line from the hydraulic
radius scale of 0.5 feet through the point on the reference
line extending this to the head-loss scale which will
determine
the slope of the channel. In this case about 10 feet of head
will be lost per thousand feet of channel. If the channel is
100 feet long, the loss would only be 1.0 feet--if 50 feet
long, 0.5 feet, and so forth.
Pipe Bead Loss and Penstock Intake
The trashrack consists of a number of vertical bars welded
to
an angle iron at the top and a bar at the bottom (see Figure
below).
owd10x61.gif (600x600)
The vertical bars must be spaced so that the teeth of a
rake can penetrate the rack for removing leaves, grass, and
trash which might clog up the intake. Such a trashrack can
easily
be manufactured in the field or in a small welding shop.
Downstream from the trashrack, a slot is provided in the
concrete
into which a timber gate can be inserted for shutting off
the flow of water to the turbine.
The penstock can be constructed from commercial pipe. The
pipe
must be large enough to keep the head loss small. The required
pipe size is determined from the nomograph. A straight line
ngraph3.gif (600x600)
drawn through the water velocity and flow rate scales gives
the
required pipe size and pipe head loss. Head loss is given
for a
100-foot pipe length. For longer or shorter penstocks, the
actual head loss is the head loss from the chart multiplied
by
the actual length divided by 100. If commercial pipe is too
expensive, it is possible to make pipe from native material;
for example, concrete and ceramic pipe, or hollowed logs.
The
choice of pipe material and the method of making the pipe
depend on the cost and availability of labor and the
availability
of material.
APPENDIX II
SMALL DAM CONSTRUCTION
This appendix is not designed to be exhaustive; it is meant
to
provide background and perspective for thinking about and
planning dam efforts. While dam construction projects can
range
from the simple to the complex, it is always best to consult
an
expert, or even several; for example, engineers for their
construction
savvy and an environmentalist or concerned agriculturalist
for a view of the impact of damming.
Introduction to:
Earth Dams
owd11650.gif (600x600)
Crib Dams
owd13670.gif (600x600)
Concrete and Masonry Dams
EARTH DAMS
An earth dam may be desirable where concrete is expensive
and
timber scarce. It must be provided with a separate spillway
of
sufficient size to carry off excess water because water can
never be allowed to flow ovewr the crest of an earth dam.
Still
water is held satisfactorily by earth but moving water is
not.
The earth will be worn away and the dam destroyed.
The spillway must be lined with boards or concrete to
prevent
seepage and erosion. The crest of the dam may be just wide
enough for a footpath or may be wide enough for a roadway,
with
a bridge placed across the spillway.
The big problem in earth-dam construction is in places where
the dam rests on solid rock. It is hard to keep the water
from
seeping between the dam and the earth and finally
undermining
the dam.
One way of preventing seepage is to blast and clean out a
series of ditches, or keys, in the rock, with each ditch about
a foot deep and two feet wide extending under the length of
the
dam. Each ditch should be filled with three or four inches
of
wet clay compacted by stamping it. More layers of wet clay
can
then be added and the compacting process repeated each time
until the clay is several inches higher than bedrock.
The upstream half of the dam should be of clay or heavy clay
soil, which compacts well and is impervious to water. The
downstream side should consist of lighter and more porous
soil
which drains quickly and thus makes the dam more stable than
if
it were made entirely of clay.
CRIB DAMS
The crib dam is very economical where lumber is easily
available: it
requires only rough tree trunks, cut planking,
and stones. Four- to
six-inch tree trunks are placed 2-3 feet
apart and spiked to others placed across them at right
angles.
Stones fill the spaces between timbers.
The upstream side
(face) of the dam, and sometimes the downstream side, is
covered with planks.
The face is sealed with clay to prevent
leakage. Downstream
planks are used as an apron to guide the
water which overflows the dam back into the stream bed.
The dam
itself serves as a spillway in this case.
The water coming over
the apron falls rapidly.
Prevent erosion by lining the bed
below with stones.
The apron consists of a series of steps for
slowing the water gradually.
Crib dams must be embedded well into the embankments and
packed
with impervious material such as clay or heavy earth and
stones
in order to anchor them and to prevent leakage.
At the heel, as
well as at the toe of crib dams, longitudinal rows of planks
are driven into the stream bed.
These are priming planks which
prevent water from seeping under the dam, and they also
anchor
it.
If the dam rests on rock, priming planks cannot and need not
be
driven; but where the dam does not rest on rock they make it
more stable and watertight.
These priming planks should be
driven as deep as possible and then spiked to the timber of
the
crib dam.
The lower ends of the priming planks are pointed as shown in
the Figure on page 69 and must be placed one after the other
as
figx69.gif (600x600)
shown. Thus each
successive plank is forced, by the act of
driving it closer against the preceding plank, resulting in
a
solid wall. Any
rough lumber may be used. Chestnut and
oak are
considered to be the best material.
The lumber must be free
from sap, and its size should be approximately 2" X
6".
In order to drive the priming planks, considerable force may
be
required. A simple
pile driver will serve the purpose. The
Figure below shows an excellent example of a pile driver.
CONCRETE AND MASONRY DAMS
Concrete and masonry dams more than 12 feet high should not
be
built without the advice of an engineer with experience in
this
field. Dams require
knowledge of the soil condition and bearing
capacity as well as of the structure itself.
A stone dam can also serve as a spillway.
It can be up to 10
owd15x70.gif (486x486)
feet in height. It
is made of rough stones. The layers
should
be bound by concrete.
The dam must be built down to a solid and
permanent footing to prevent leakage and shifting.
The base of
the dam should have the same dimensions as its height to
give
it stability.
Small concrete dams should have a base with a thickness 50
owd16x71.gif (437x437)
percent greater than height.
The apron is designed to turn the
flow slightly upwards to dissipate the energy of the water
and
protect the downstream bed from erosion.
APPENDIX III
PUMP SELECTION
Design for a Simple Pump
PUMP SELECTION
One choice for a water-powered pump is a positive
displacement
pump. Such pumps are
called by various names: bucket pump,
lift
pump, piston pump, windmill pump, and occasionally even
simply
by brand name, such as "Rocket" pump.
Numerous models are
available commercially and vary in cost from a few dollars
for
small capacity pumps to several hundred for high capacity, high
head, durable, well manufactured units.
However, pumps can be
manufactured at low cost in the simplest of workshops.
One single acting pump attached to the wheel will cause
speed
surges on the wheel because actual pumping takes place only
half the time, while the other half is spent filling the
cylinder. During the
filling stage, considerably less wheel
torque is required than when pumping is being done.
The speed
surge can be partially overcome by using:
* Two single-acting
pumps 180[degrees] out of phase so that one of the
owd17x75.gif (437x437)
pumps is always
doing useful work.
* A double-acting
pump which
owd18x76.gif (486x486)
has the same
effect as the
one above but is
built in
one unit; or
* best of all, two
double-acting
owd19x76.gif (353x437)
pumps 90[degrees]
out of phase.
Use of multiple simple pumps improves the overall efficiency
of
the system. (In
general, one unit can be attached easily to a
crank at each end of the wheel shaft.)
Table 1. Quantities
of Water Pumped Per Stroke for
Single-Acting Pumps of Various Bore and Stroke Sizes
(Imperial
Gallons)
Stroke (in.)
Bore (in.)
2-1/4 4
6
8 10
12
1-1/4
.009 .016
.023
.032 .040
.049
1-1/2
.013 .023
.035
.045 .057
.069
2
.023 .040
.062
.082 .102
.122
2-1/2
.035 .064
.095
.127 .159
.191
3
.052
.092
.139 .184
.230
.278
3-1/2
.070 .125
.187
.248 .312
.276
4
.092 .163
.245
.227 .410
.489
5
.143 .255
.382
.510 .638
.765
DESIGN FOR A SIMPLE PUMP
An Easily Constructed Piston Pump
This pump <see figure> was designed by P. Brown
owd20x78.gif (600x600)
(of the Mechanical Engineering
Workshop at the Papua New Guinea
University of Technology) with a
view to manufacture in Papua New
Guinea. Consequently
the pump can
be built using a minimum of workshop
equipment--most parts are
standard pipe fittings available
from any plumbing supplier.
A PVC pipe can be used in place of
copper pipe. This
eliminates the
need for a pipe reducer.
The PVC
pipe can have a uniform diameter
throughout.
To avoid having to bore and hone a
pump cylinder, a length of copper
or PVC pipe is used.
If care is
taken to select an undamaged
length of pipe and to see that the
pipe is not damaged during construction,
this system has proved
quite satisfactory.
As can be seen from the cross-sectional
diagram, the ends of the
pump body consist of copper pipe
reducers silver-soldered onto the
pump cylinder. This
does make disassembly
of the pump difficult,
but avoids the use of a lathe.
If a lathe is available, a screwed end could be
silver-soldered
to the upper end of the pump to allow for simple
disassembly.
The piston of the pump consists of a 1/2" thick PVC
flange with
holes drilled through it (see diagram on page 78).
A leather
bucket is attached above the piston and together with the
holes
serves as a non-return valve.
In this type of pump the bucket
must be made of fairly soft leather, a commercial leather
bucket is not suitable.
Bright steel bar is used as the drive
rod. Threads must be
cut into the ends of the rod with a die.
A galvanized nipple is silver-soldered to the top copper
reducer of the pump to allow the discharge pipe to be
attached.
An `O' ring seal of the type used to join PVC pipe is used
as a
seal for the foot valve.
This seal does not require any fixing
since it push fits into the lower copper pipe reducer.
A 1/2"
screwed flange with a plug in its center forms the plate for
the foot valve. This
plate is prevented from rising up the bore
of the pump by three brass pegs fitted in through the
sidewall
of the pump above the valve plate.
Silver-solder the pegs to
prevent leakage or movement.
Parts and tools for a 4" bore X 9" stroke pump
include the
following:
Parts
1 12" X 4"
dia copper tube
2 4" to
1/2" copper tube reducers
1 1-1/2"
galvanized nipple
1 1/2" screwed
flange
1 1/2" plug
1 1/2" PVC
flange
1 rubber `O' ring,
4" dia
1 4-1/2" dia
piece of leather
1 15" X
1/2" dia bright steel bar
1 1/8" dia
brazing rod
Tools
Handi gas kit
Silver solder
Hand drill
1/2" Whitworth die
1/2" Whitworth tap
Hacksaw
Hammer
APPENDIX IV
CALCULATING BEARING AND SHAFT SIZES
CALCULATING BEARING SIZE
Because it is very likely that people using this material
will
want to change the size of the waterwheel they construct,
the
following information is provided to serve as a basis for
determining the size of the bearings which must be used.
Approximate Weight Carried by Each
Bearing
Excluding Loads Due to Attached Machinery
(per Meter of Width of the Wheel) (kg)
Annulus
Outside Diameter (cm)
Width (cm)
91.5 122
183
244 305
427
610
5
11
14.5 23
7.5
16
21.5 32
43
54.5
10
20
27.3 40.5
57
73
15
39
64
84 107
152
214
20
82
109
139 200
307
25
132 168
241
348
30
150 202
289
418
40
373
552
50
464
682
60
800
Bearing diameters required to support the various loads are
given in the table on the following page calculated on the
basis of 100 psi (i.e., a hardwood such as oak) in parallel
usage and 200 psi for end grain usage. Values are given to
90.90 kgs to allow for the largest reasonable bearing loads.
---------------
(*) Outside wheel diameter minus inside wheel diameter
divided by
2.
Minimum Bearing Inside Diameter Required
For Various Loadings (cm)
Load (kg)
45.5
91
227 454
908
2272 4545
9090
Parallel
Usage
2.5
3.8 5.75
8.25
10.88 17.75
25.5
35.5
End Grain
Usage
1.5
2.5 4.5
5.75
8.25 12.5
17.75
25.5
These bearings are assumed to be steel on wood. It is likely
owd20x84.gif (540x540)
that with metal shafts used in the larger sizes of
waterwheels,
the bearing will be considerably larger than the required
shaft
size. A "built-up and banded" bearing may be used.
This is
accomplished by attaching a wooden cylinder to the wheel
shaft
at the bearing location to bring the cylinder's outside
diameter
to the necessary size. Then steel bands are bent and
fastened to the cylinder.
Calculating Shaft Size
Waterwheel shafts may be made of wood or steel. The diameter
of
the shaft depends on the material used and the dimensions of
the wheel. The tables below give minimum shaft diameters for
bearing loads up to 45.45 kgs.
Minimum Standard Pipe Sizes for Use as Acles
With Bearings at 30cm From Wheel Edge
Metal Shafts)
Bearing Load (kg)
45.5 91
227
454 908
2270
4540
Pipe Diameter cm)
Solid Metal Shaft
2.5 3.75
6.25
7.5 10
15
20
Minimum Standard Hardwood Sizes for Use as Axles
With Bearings at 30cm From Wheel Edge
(Wooden Shafts)
Bearing Load (kg)
45.5 91
227
454
908 2270
4540
Wood Shaft
Diameter (cm)
3.75 6.25
9
18 33
86.5
173
When comparing these figures with the bearing diameters, it
can
be seen that for pipe or a solid steel shaft, a wooden
bearing
will need to be built up. With wooden shafts, the required
shaft diameter will usually exceed the required bearing
diameter
giving one the choice of reducing the shaft diameter at the
bearing location (but only there) or of using larger
bearings.
In either case, the shaft must be banded with steel, sleeved
with a piece of pipe, or given some similar protection
against
wear in the bearing.
APPENDIX V
DECISION MAKING WORKSHEET
If you are using this as a guideline for using the
Waterwheel
in a development effort, collect as much information as
possible and if you need assistance with the project, write
VITA. A report on your experiences and the uses of this
manual
will help VITA both improve the book and aid other similar
efforts.
VOLUNTEERS IN TECHNICAL ASSISTANCE
1600 Wilson Boulevard, Suite 500
Arlington, Virginia 22209, USA
CURRENT USE AND AVAILABILITY
* Describe current
agricultural and domestic practices which
rely on water at
some point.
* What water power
sources are available? Include rivers,
streams, lakes,
ponds. Note whether sources are small but
fast-flowing,
large but slow-flowing, etc.
* What is water used
for traditionally?
* Is water currently
being used to provide power for any
purpose? If so,
what and with what positive or negative
results?
* Are there dams
already built in the area? If so, what have
been the effects
of the damming? Note particularly any
evidence having to
do with the amount of sediment carried by
the water--too
much sediment can create a swamp.
* If water resources
are not now harnessed, what seem to be
the limiting
factors? Does the cost of the effort seem
prohibitive? Does
the lack of knowledge of water potential
limit its use?
NEEDS AND RESOURCES
* Based on current
agricultural and domestic practices, what
seem to be the
areas of greatest need? Is power needed to
run currently
hand-powered machines such as grinders, saws,
pumps?
* What are the
characteristics of the problems? Is the local
population aware
of the problem/need? How do you know?
* Has any local
person, particularly someone in a position of
authority,
expressed the need or expressed any interest in
this technology/
If so, can someone be found to help the
technology
introduction process?
* Are there local
officials who could be involved and tapped
as resources?
* How can you help
the community decide which technology is
appropriate for
them?
* Given water power
sources available which water resources
seem to be
available and most useful? For example, one
stream which runs
quickly year around and is located near to
the center of
agricultural activity may be the only feasible
source to tap for
power.
* Define water power
sites in terms of their inherent
potential for
power generation. In other words, one water
source may be a
power resource only if harnessed by an
expensive turbine.
* Are any materials
for constructing water power technologies
available locally?
Are local skills sufficient? Some water
power applications
demand a rather high degree of
construction
skill. Is surveying equipment available? Do you
need to train
people?
* Can you meet the
following needs?
*
Some aspects of the waterwheel project
require someone
with experience
in woodworking and surveying.
*
Estimated labor time for full-time workers
is:
*
4 hours skilled labor
*
40 hours unskilled labor.
*
If this is a part-time project, adjust the
times
accordingly.
* Do a cost estimate
of the labor, parts, and materials
needed.
* Does the
technology require outside funding? Are local
funding sources
available?
* What is your
schedule? Are you aware of holidays and
planting or
harvesting seasons which may affect timing?
* How will you
spread information on, and promote use of, the
technology?
IDENTIFY APPROPRIATE TECHNOLOGY
* Is more than one
water power technology applicable? Weigh
the costs of
various technologies relative to each other--fully
in terms of labor,
skill required, materials,
installation and
operation costs. Remember to look at all
the costs.
* Are there choices
to be made between say a waterwheel and a
windmill to
provide power for grinding grain? Again weigh
all the costs:
feasibility, economics of tools and labor,
operation and
maintenance, social and cultural dilemmas.
* Are there local skilled
resources to guide technology
introduction in
the water power area?
* Where the need is
sufficiently large-scale and resources are
available,
consider a manufactured turbine and a group
effort to build
the dam and otherwise install the turbine.
* Could a technology
such as the hydraulic ram be usefully
manufactured and
distributed locally? Is there a possibility
of providing a
basis for a small business enterprise?
FINAL DECISION
* How was the final
decision reached to go ahead--or not go
ahead--with this
technology?
APPENDIX VI
RECORD KEEPING WORKSHEET
CONSTRUCTION
Photographs of the construction process, as well as the
finished result, are helpful. They add interest and detail
that
might be overlooked in the narrative.
A report on the construction process should include much
very
specific information. This kind of detail can often be
monitored
most easily in charts (such as the one below). <see
report 1>
owdr1910.gif (486x486)
Some other things to record include:
* Specification of
materials used in construction.
* Adaptations or
changes made in design to fit local
conditions.
* Equipment costs.
* Time spent in
construction--include volunteer time as well
as paid labor;
full- or part-time.
* Problems--labor
shortage, work stoppage, training difficulties,
materials
shortage, terrain, transport.
OPERATION
Keep log of operations for at least the first six weeks,
then
periodically for several days every few months. This log
will
vary with the technology, but should include full
requirements,
outputs, duration of operation, training of operators, etc.
Include special problems that may come up--a damper that
won't
close, gear that won't catch, procedures that don't seem to
make sense to workers, etc.
MAINTENANCE
Maintenance records enable keeping track of where breakdowns
occur most frequently and may suggest areas for improvement
or
strengthening weakness in the design. Furthermore, these
records will give a good idea of how well the project is
working out by accurately recording how much of the time it
is
working and how often it breaks down. Routine maintenance
records should be kept for a minimum of six months to one
year
after the project goes into operation. <see report 2>
owdr2x93.gif (486x486)
SPECIAL COSTS
This category includes damage caused by weather, natural
disasters,
vandalism, etc. Pattern the records after the routine
maintenance records. Describe for each separate incident:
* Cause and extent
of damage.
* Labor costs of
repair (like maintenance account).
* Material costs of
repair (like maintenance account).
* Measures taken to
prevent recurrence.
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