SMALL MICHELL (BANKI) TURBINE:
A CONSTRUCTION MANUAL
a VITA publication
1600 Wilson Boulevard, Suite 500
Arlington, Virginia 22209 USA
Tel: 703/276-1800 * Fax:
1980 Volunteers in Technical Assistance
SMALL MICHELL (BANKI) TURBINE:
A CONSTRUCTION MANUAL
WHAT IT IS AND WHAT IT IS USED FOR
MAKING THE DECISION AND FOLLOWING
Assemble the Turbine
VIII. DICTIONARY OF
FURTHER INFORMATION RESOURCES
APPENDIX I. SITE
APPENDIX II. SMALL
DECISION MAKING WORKSHEET
APPENDIX IV. RECORD
SMALL MICHELL (BANKI) TURBINE
I. WHAT IT IS AND
HOW IT IS USEFUL
The Michell or Banki turbine is a relatively easy to build
highly efficient means of harnessing a small stream to
enough power to generate electricity or drive different
of mechanical devices.
The turbine consists of two main parts--the runner, or
and the nozzle.
Curved horizontal blades are fixed between the
circular end plates of the runner (see page 17).
from the nozzle through the runner twice in a narrow jet
it is discharged.
Once the flow and head of the water site have been
the blades of the 30cm diameter wheel presented here can be
lengthened as necessary to obtain optimum power output from
available water source.
The efficiency of the Michell turbine is 80 percent or
This, along with its adaptability to a variety of water
sites and power needs, and its simplicity and low cost, make
very suitable for small power development.
The turbine itself
provides power for direct current (DC); a governing device
necessary to provide alternating current (AC).
II. DECISION FACTORS
* Electric generation (AC or DC)
* Machinery operations, such as
winnower, water pumping, etc.
* Very efficient and simple to
Virtually no maintenance.
* Can operate over a range of
water flow and
* Requires a certain amount of
skill in working
Special governing device is needed for AC
* Welding equipment with cutting
* Electric grinding machine is
to small machine shop is necessary.
$150 to $600 (US, 1979) including materials and labor.
for the turbine only.
Planning and construction costs of dam,
penstock, etc., must be added.)
(*) Cost estimates serve only as a guide and will vary from
country to country.
Development of small water power sites currently comprises
of the most promising applications of alternate energy
If water power will be used to produce only mechanical
energy--for example, for powering a grain thresher--it may
easier and less expensive to construct a waterwheel or a
However, if electrical generation is needed, the Michell
turbine, despite relatively high initial costs, may be
and indeed economical under one or more of the following
* Access to
transmission lines or to reliable fossil fuel
sources is limited
* Cost of fossil and
other fuels is high.
* Available water
supply is constant and reliable, with a head
relatively easy to achieve.
* Need exists for
only a small dam built into a river or stream
and for a
relatively short (less than 35m) penstock (channel)
water to the turbine.
If one or more of the above seems to be the case, it is a
idea to look further into the potential of a Michell
The final decision will require consideration of a
of factors, including site potential, expense, and purpose.
III. MAKING THE
DECISION AND FOLLOWING THROUGH
When determining whether a project is worth the time,
and expense involved, consider social, cultural, and
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
keep good records.
It is helpful from the beginning to keep
data on needs, site selection, resource availability,
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
energy series have been tested carefully and are actually
in many parts of the world.
However, extensive and controlled
field tests have not been conducted for many of them, even
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
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
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
exists to help spread the word about these and other
lessening the dependence of the developing world on
expensive and finite energy resources.
A practical record keeping format can be found in Appendix
Both main parts of the Michell turbine are made of plate
and require some machining.
Ordinary steel pipe is cut to form
the blades or buckets of the runner.
Access to welding equipment
and a small machine shop is necessary.
The design of the turbine avoids the need for a complicated
The bearings have no contact with the
water flow, as they are located outside of the housing; they
can simply be lubricated and don't need to be sealed.
Figure 2 shows an arrangement of a turbine of this type for
low-head use without control.
This installation will drive an
AC or DC generator with a belt drive.
This is a very important factor.
The amount of power obtained,
the expense of installation, and even, by extension, the
for which the power can be used may be determined by
the quality of the site.
The first site consideration is ownership.
Installation of an
electricity-generating unit--for example, one that needs a
and reservoir in addition to the site for the housing--can
require access to large amounts of land.
In many developing countries, large lots of land are few and
is likely that more than one owner will have to be
If ownership is not already clearly held, the property
must be investigated, including any rights which may
belong to those whose property borders on the water.
for example, can change the natural water flow and/or water
usage patterns in the area and is a step to be taken only
If ownership is clear, or not a problem, a careful analysis
the site is necessary in order to determine:
1) the feasibility
of the site for use of any kind, and 2) the amount of power
obtainable from the site.
Site analysis consists of collecting the following basic data:
* Minimum flow.
* Maximum flow.
* Available head
(the height a body of water falls before hitting
* Pipe line length
(length of penstock required to give desired
* Water condition
(clear, muddy, sandy, acid, etc.).
* Site sketch (with
evaluations, or topographical map with site
* Soil condition
(the size of the ditch and the condition of
the soil combine
to affect the speed at which the water moves
channel and, therefore, the amount of power
* Minimum tailwater
(determines the turbine setting and type).
Appendix I contains more detailed information and the
needed to complete the site analysis including directions
for measuring head, water flow, and head losses.
are simple enough to be carried out in field conditions
without a great deal of complex equipment.
Once such information is collected, the power potential can
determined. Some power, expressed in terms of horsepower or
kilowatts (one horsepower equals 0.7455 kilowatts), will be
lost because of turbine and generator inefficiencies and
it is transmitted from the generator to the place of
For a small water power installation of the type considered
here, it is safe to assume that the net power (power
delivered) will be only half of the potential gross power.
Gross power, or power available directly from the water, is
determined by the following formula:
Gross power (English
units: horsepower) =
Minimum Water Flow (cubic feet/second) X Gross Head (feet)
Gross power (metric
1,000 Flow (cubic meters/second) X Head (meters)
Net Power (available at the turbine shaft)
Net Power (English
Minimum Water Flow X Net Head(*) X Turbine Efficiency
Net Power (metric
Minimum Water Flow X Net Head(*) X Turbine Efficiency
Some sites lend themselves naturally to the production of
electrical or mechanical power.
Other sites can be used if work
is done to make them suitable.
For example, a dam can be built
to direct water into a channel intake or to get a higher
than the stream provides naturally.
(A dam may not be required
if there is sufficient head or if there is enough water to
cover the intake of a pipe or channel leading to the
Dams may be of earth, wood, concrete, or stone.
provides some information on construction of small dams.
Flowing water tends to generate automatically a picture of
"free" power in the eyes of the observer.
But there is always a
(*) Net head is obtained by deducting energy losses from the
head (see page 57).
A good assumption for turbine efficiency
when calculating losses is 80 percent.
cost to producing power from water sources. Before
the cost of developing low-output water power sites should
checked against the costs of other possible alternatives,
utility--In areas where transmission lines can furnish
of reasonably priced electric current,
it is often
uneconomical to develop small or medium-sized
However, in view of the increasing cost of
electricity, hydroelectric power is becoming more
engines and internal-combustion engines
are available in a
wide variety of sizes and use a variety of
fuels--for example, oil, gasoline, or
wood. In general, the
expenditure for this type of power plant is low compared
to a hydroelectric
plant. Operating costs, on the other
hand, are very low
for hydroelectric and high for fossil fuel
work has been done on the utilization of
solar energy for
such things as water pumping. Equipment
available may be
less costly than water power development in
regions with long
hours of intense sunshine.
If it seems to make sense to pursue development of the small
water power site, it is necessary to calculate in detail
whether the site will indeed yield enough power for the
Some sites will require investing a great deal more money
of dams and penstocks can be very expensive,
depending upon the size and type of dam and the length of
the channel required.
Add to these construction expenses, the
cost of the electric equipment--generators, transformers,
transmission lines--and related costs for operation and
and the cost can be substantial.
Any discussion of site or cost, however, must be done in
of the purpose for which the power is desired.
It may be
possible to justify the expense for one purpose but not for
ALTERNATING OR DIRECT CURRENT
A turbine can produce both alternating (AC) and direct
(DC). Both types of
current cannot always be used for the same
purposes and one requires installation of more expensive
than the other.
Several factors must be considered in deciding whether to
install an alternating or direct current power unit.
The demand for power will probably vary from time to time
the day. With a
constant flow of water into the turbine,
the power output will thus sometimes exceed the demand.
In producing AC, either the flow of water or the voltage
be regulated because AC cannot be stored.
Either type of regulation
requires additional equipment which can add substantially
to the cost of the installation.
The flow of water to a DC-producing turbine, however, does
have to be regulated.
Excess power can be stored in storage
current generators and storage batteries are
relatively low in cost because they are mass-produced.
Direct current is just as good as AC for producing electric
light and heat. But
electrical equipment having AC motors,
such as farm machinery and household appliances, have to be
changed to DC motors.
The cost of converting appliances must be
weighed against the cost of flow regulation needed for
While a 30.5cm diameter wheel has been chosen for this
because this size is easy to fabricate and weld, the Michell
turbine has a wide range of application for all water power
sites providing head and flow are suitable.
The amount of water
to be run through the turbine determines the width of the
nozzle and the width of the wheel. These widths may vary
5cm to 36cm. No
other turbine is adaptable to as large a range
of water flow (see Table 1).
Impulse or Pelton Michell
or Banki Centrifugal Pump
Used as Turbine
Head Range (feet
) 50 to 1000
3 to 650
Flow Range (cubic)
second 0.1 to 10
0.5 to 250
Available for any
(horsepower) 1 to 500
1 to 1000
James Leffel & Co.
Any reputable dealer
Springfield, Ohio 8832
Warenburg or manufacturer.
45501 USA Bayern,
Dress & Co. Can
Warl. Germany project
if small weld and
Offices Bubler machine
Table 1. Small Hydraulic Turbines
The size of the turbine depends on the amount of power
required, whether electrical or mechanical.
Many factors must
be considered to determine what size turbine is necessary to
the job. The
example illustrates the
for the use of a turbine
to drive a peanut huller
(see Figure 3).
be similar in electrical
* Power enough to
the motor for a
* Gross power needed
is about 5 hp (roughly twice the horsepower
of the motor to be
replaced assuming that the losses
are about one-half
of the total power available).
* Village stream can
be dammed up and the water channeled
through a ditch
30m (100 ft) long.
* Total difference
in elevation is 7.5m (25 ft).
* Available minimum
flow rate: 2.8 cu ft/sec.
* Soil of ditch
permits a water velocity of 2.4 ft/sec (Appendix
I, Table 2 gives n
* Area of flow in
ditch = 2.8/2.4 - 1.2 sq ft.
* Bottom width = 1.2
* Hydraulic radius =
0.31 x 1.2 = 0.37 ft (see Appendix I).
Calculate results of fall and head loss.
Shown on nomograph
(Appendix I) as a 1.7 foot loss for every 1,000 feet.
the total loss for a 30m (100 ft) ditch is:
10 = 0.17 feet
Since 0.17 ft is a negligible loss, calculate head at 25 ft.
Power produced by turbine at 80% efficiency = 6.36 hp
Net power = Minimum water flow x net head x turbine
2.8 x 25 x
8.8 = 6.36 horsepower
Formulas for principal Michell turbine dimensions:
([B.sub.1]) = width
of nozzle = 210 x flow
Runner outside diameter x [square
210 x 2.8 = 9.8 inches
12 x [square root] 25
([B.sub.2]) = width
of runner between discs - ([B.sub.1]) = 1/2 to 1 inch
= 9.8 + 1 inch = 10.8 inches
(revolutions per minute)
73.1 x [square root] head
Runner outside diameter (ft)
73.1 x [square root] 25
= 365.6 rpm
generated is more than enough for the peanut
huller but the rpm
is not high enough.
threshers will operate at varying speeds with
of hulled peanuts. So for a huller which
gives maximum output
at 2-1/2 hp and 1800 rpm, a pulley
arrangement will be
needed for stepping up speed. In this
example, the pulley
ratio needed to step up speed is 1800
approximately 5:1. Therefore a 15"
pulley attached to
the turbine shaft,
driving a 3" pulley on a generator shaft,
will give [+ or -]
Although materials used in construction can be purchased
many of these materials can be found at junk yards.
Materials for 30.5cm diameter Michell turbine:
* Steel plate 6.5mm
X 50cm X 100cm
* Steel plate 6.5mm
thick (quantity of material depends on
* 10cm ID water pipe
for turbine buckets(*)
* Chicken wire
(1.5cm X 1.5cm weave) or 25mm dia steel rods
* 4 hub flanges for
attaching end pieces to steel shaft (found
on most car axles)
* 4.5cm dia solid
* two 4.5cm dia
pillow or bush bearings for high speed use.
is possible to
fabricate wooden bearings. Because of
bearings would not last and are not recommended.)
* eight nuts and
bolts, appropriate size for hub flanges
* Welding equipment
with cutting attachments
* Metal file
* Electric or manual
* Drill and metal
* Compass and
* T-square (template
included in the back of this manual)
* Work bench
(*) Measurements for length of the pipe depend on water site
PREPARE THE END PIECES
An actual size template for a 30.5cm turbine is provided at
end of this manual.
Two of the bucket slots are shaded to show
how the buckets are installed.
Figure 4 shows the details of a Michell runner.
* Cut out the half
circle from the template and mount it on
cardboard or heavy
* Trace around the
half circle on the steel plate as shown in
* Turn the template
over and trace again to complete a full
circle (see Figure 6.
* Draw the bucket
slots on the template with a clockwise slant
as shown in Figure
* Cut out the bucket
slots on the template so that there are 10
* Place the template
on the steel plate and trace in the
* Repeat the tracing
process as before to fill in the area for
the shaft (see
* Drill a 2mm hole
in the steel plate in the center of the
wheel where the
cross is formed. The hole will serve as
guide for cutting
the metal plate.
* Take a piece of
scrap metal 20cm long x 5cm wide. Drill
hole the width of
the opening in the torch near one end of
the metal strip.
* Drill a 2mm dia
hole at the other end at a point equal to the
radius of the
wheel (15.25cm). Measure carefully.
* Line up the 2mm
hole in the scrap metal with the 2mm hole in
the metal plate
and attach with a nail as shown in Figure 10.
* Cut both end
plates as shown (in Figure 10) using the torch.
* Cut the bucket
slots with the torch or a metal saw.
* Cut out a 4.5cm
dia circle from the center of both wheels.
This prepares them
for the axle.
CONSTRUCT THE BUCKETS
Calculate the length of buckets using the following formula:
210 x Flow (cu/ft/sec)
+ (1 .5in)
Plates Outside Diameter of
Turbine (in) x [square root] Head (ft)
* Once the bucket
length has been determined, cut the 10cm dia
pipe to the
* When cutting pipe
lengthwise with a torch, use a piece of
angle iron to
serve as a guide, as shown in Figure 11.
measurements given in the template in the back of
this manual will
serve as a guide.)
* Pipe may also be
using an electric
circular saw with
* Cut four buckets
from each section of pipe. A fifth
pipe will be left
over but it will not be the correct width
or angle for use
as a bucket (see Figure 12).
* File each of the
buckets to measure 63mm wide.
with a torch may
warp the buckets. Use a hammer to
out any warps.)
ASSEMBLE THE TURBINE
* Cut a shaft from
4.5cm dia steel rod. The total length
shaft should be
60cm plus the width of the turbine.
* Place the metal
hubs on the center of each end piece, matching
the hole of the
hub with the hole of the end piece.
* Drill four 20mm
holes through the hub and end piece.
* Attach a hub to
piece using 20mm
3cm long bolts and
* Slide shaft
hubs and space the
pieces to fit the
* Make certain the
distance from each end piece to the end of
the shaft is 30cm.
* Insert a bucket
and align the end pieces so that the blade
parallel with the center shaft.
* Spot weld the
bucket in place from the outside of the end
piece (see Figure
* Turn the turbine
on the shaft half a revolution and insert
making sure it is aligned with the center
* Spot weld the
second bucket to the end pieces. Once
placed, it is easier to make sure that all the
buckets will be
aligned parallel to the center shaft.
* Weld the hubs to
the shaft (check measurements).
* Weld the remaining
buckets to the end pieces (see Figure 15).
* Mount the turbine
on its bearings. Clamp each bearing to
workbench so that the
whole thing can be slowly rotated as in
The cutting tool is an electric or small
mounted on a rail and allowed to slide along a
second rail, or
guide (see Figure 16). The slide rail
be carefully clamped
so that it is exactly parallel to the
* Grind away any
uneven edges or joints. Rotate the
slowly so that the
high part of each blade comes into contact
grinder. Low parts will not quite
several hours and must be done carefully.
* Make sure the
bucket blades are ground so that the edges are
flush with the
outside of the end pieces.
* Balance the
turbine so it will turn evenly (see Figure 17).
It may be
necessary to weld a couple of small metal washers
on the top of
either end of the turbine. The turbine
balanced when it
can be rotated in any position without
MAKE THE TURBINE NOZZLE
* Determine nozzle
size by using the following formula:
210 X flow (cubic feet/second
outside diameter (in) x [square root] head (ft)
The nozzle should
be 1.5cm to 3cm less than the inside width
of the turbine.
Figure 18 shows a front view of a properly positioned nozzle
relationship to the turbine.
* From a 6.5mm steel
plate, cut side sections and flat front
and back sections
of the nozzle. Width of front and back
pieces will be
equal to the width of the turbine wheel minus
1.5 to 3cm.
Determine other dimensions from the
diagram in Figure 19.
* Cut curved
sections of the nozzle from 15cm (OD) steel pipe
Make sure that the pipe is first cut to the
correct width of
the nozzle as calculated previously.
steel plate to the
necessary curvature if 15cm pipe is
The process will take some time and
the part of the
builder. One way of bending steel plate
sledge hammer the plate around a steel
cylinder or hardwood
log 15cm in
diameter. This may be the only way to
the nozzle if 15cm
steel pipe is unavailable.)
* Weld all sections
together. Follow assembly instructions
"Turbine Housing" on page 29.
The diagram in Figure 19 provides minimum dimensions for
Build the structure
to house the turbine and nozzle of concrete,
wood, or steel
plate. Figure 20 shows a side view and
front view of a
typical installation for low head use
Be sure housing allows for easy access to
for repair and
* Attach the nozzle
to the housing first and then orient the
turbine to the
nozzle according to the dimensions given in
the diagram in
Figure 19. This should ensure correct
Mark the housing for the placement of the
* Make water
seals. In 6.5mm steel plate, drill a
larger than the
shaft diameter (about 4.53cm). Make one
Weld or bolt to the inside of the turbine
The shaft must
pass through the seals without touching
Some water will still come through the
housing but not
interfere with efficiency.
* Make the
foundation to which the bearings will be attached of
* Move the turbine,
with bearings attached, to the proper
placement and attach the bearings to the foundation
The bearings will be on the outside of the
(see Figure 21). (Note:
The drive pulley is
omitted from the
Figure for clarity.)
Figure 22 shows a possible turbine installation for high
water shut-off valve allows control of the flow
of water. Never shut
off the water flow suddenly as a rupture
in the penstock is certain to occur.
If maintenance on the turbine
is necessary, reduce the flow gradually until the water
The Michell (Banki) turbine is relatively
only wearable parts are the bearings which may have to be
replaced from time to time.
An unbalanced turbine or a turbine that is not mounted
will wear the bearings very quickly.
A chicken wire screen (1.5cm x 1.5cm weave) located behind
control gate will help to keep branches and rocks from
the turbine housing.
It may be necessary to clean the screen
from time to time.
An alternative to chicken wire is the use of
thin steel rods spaced so that a rake can be used to remove
leaves or sticks.
It is beyond the scope of this manual to go into electrical
generation using the Michell (Banki) turbine.
Depending on the
generator and accessories you choose, the turbine can
enough rpm for direct current (DC) or alternating current
For information on the type of generator to purchase,
A list of companies is provided here.
The manufacturer often will be able to recommend an
generator, if supplied with enough information upon which to
make a recommendation.
Be prepared to supply the following
* AC or DC operation
(include voltage desired).
* Long range use of
electrical energy (future consumption and
* Climatic condition
under which generator will be used (i.e.,
temperate, arid, etc.).
* Power available at
water site calculated at lowest flow and
* Power available to
the generator in watts or horsepower (conservative
figure would be
half of power at water site).
* Revolutions per
minute (rpm) of turbine without pulleys and
* Intended or
present consumption of electrical energy in watts
(include frequency of electrical use).
* Lima Electric Co.,
200 East Chapman Road, Lima, Ohio 45802
* Kato, 3201 Third
Avenue North, Mankato, Minnesota 56001 USA.
* Onan, 1400 73rd
Avenue NE, Minneapolis, Minnesota 55432 USA.
* Winco of Dyna
Technologies, 2201 East 7th Street, Sioux City,
Iowa 51102 USA.
* Kohler, 421 High
Street, Kohlen, Wisconsin 53044 USA.
* Howelite, Rendale
and Nelson Streets, Port Chester, New York
* McCulloch, 989
South Brooklyn Avenue, Wellsville, New York
* Sears, Roebuck and
Co., Chicago, Illinois USA.
* Winpower, 1225 1st
Avenue East, Newton, Iowa 50208 USA.
* Ideal Electric,
615 1st Street, Mansfield, Ohio 44903 USA.
* Empire Electric
Company, 5200-02 First Avenue, Brooklyn, New
York 11232 USA.
* Bright Star, 602
Getty Avenue Clifton, New Jersey, 07015
* Burgess Division
of Clevite Corp., Gould PO Box 3140, St.
Division of GM, PO Box 2439, Anderson, Indiana
Industries, Box 47, Joplin, Missouri 64801 USA.
* ESB Inc., Willard
Box 6949, Cleveland, Ohio 44101 USA.
* Exide, 5 Penn
Center Plaza, Philadelphia, Pennsylvania 19103
* Ever-Ready Union
Carbide Corporation, 270 Park Avenue, New
York, New York
VIII. DICTIONARY OF
AC (Alternating Current)--Electrical energy that reverses
regular intervals. These intervals are
BEARING--Any part of a machine in or on which another part
DIA (Diameter)--A straight line passing completely through
center of a
DC (Direct Current)--Electrical current that flows in one
without deviation or interruption.
GROSS POWER--Power available before machine inefficiencies
HEAD--The height of a body of water, considered as causing
ID (Inside Diameter)--The inside diameter of pipe, tubing,
NET HEAD--Height of a body of water minus the energy losses
caused by the
friction of a pipe or water channel.
OD (Outside Diameter)--The outside dimension of pipe,
PENSTOCK--A conduit or pipe that carries water to a water
ROLLED EARTH--Soil that is pressed together tightly by
a steel or
heavy wood cylinder over it.
RPM (Revolutions Per Minute)--The number of times something
revolves in one minute.
TAILRACE (Tailwater)--The discharge channel that leads away
waterwheel or turbine.
TURBINE--Any of various machines that has a rotor that is
driven by the
pressure of such moving fluids as steam,
gases, or air. It is usually made with
curved blades on a central rotating spindle.
WEIR--A dam in a stream or river that raises the water
Brown, Guthrie J.
(ed.). Hydro Electric
Gordon & Breach, 1958; London:
Blackie and Sons,
A complete treatise covering the entire
engineering. Three volumes.
Vol. 2: Mechanical and Electrical
and Vol. 3:
Economics, Operation and Maintenance.
Breach Science Publishers, 440 Park Avenue South,
New York, New
York 10016 USA.
Creager, W.P. and
Justin, J.D. Hydro Electric Handbook,
York: John Wiley & Son, 1950.
A most complete
covering the entire field. Especially
John Wiley & Son, 650 Third Avenue, New
New York 10016
Davis, Calvin V.
Handbook of Applied Hydraulics, 2nd ed.
A comprehensive handbook covering
all phases of
applied hydraulics. Several chapters
hydroelectric application. McGraw-Hill,
Avenue of the
Americas, New York, New York 10020 USA.
Design of Small Water Turbines for Farms and
Adaptation Program, MIT, Cambridge,
02139 USA. A Highly technical manual
of the designs
of a Banki turbine and of axial-flow turbines.
technical drawings of their designs
and tables of
friction losses, efficiences, etc. This
manual is far
too technical to be understood without an
background. Probably only useful for
projects and the
"The Cross Flow Turbine," Water Power (London),
1960. Reprints available from Ossberger
Weissenburg, Bayern, Germany. This
describes a type
of water turbine which is being used
small power stations, especially in Germany.
Hamm, Hans W. Low
Cost Development of Small Water Power Sites.
Written expressly to be used in developing
manual contains basic information on measuring
potential, building small dams, different
turbines and water wheels, and several necessary
tables. Also has some information on
turbines available. A very useful book.
Langhorne, Harry F.
"Hand-Made Hydro Power," Alternative
Energy, No. 28, October 1977, pp.
one man built a Banki turbine from VITA
plans to power
and heat his home. useful in that it
a good account
of the mathematical calculations that were
also of the various modifications and innovations
he built into
the system. A good real-life account
of building a
low-cost water power system. ASE, Route
Box 90A, Milaca,
Minnesota 59101 USA.
Mockmore, C.A. and
The Banki Water Turbine.
Oregon: Oregon State College
Bulletin No. 25, February 1949. A
of a paper by
Donat Banki. A highly technical
this turbine, originally invented by
together with the results of tests.
Corvallis, Oregon 97331 USA.
Paton, T.A.L. Power
From Water, London: Leonard Hill,
survey of hydroelectric practice in
Zerban, A.H. and
Nye, E.P. Power Plants, 2a ed.
Pennsylvania: International Text
Book Company, 1952.
Chapter 12 gives
a concise presentation of hydraulic
plants. International Text Book
X. CONVERSION TABLES
UNITS OF LENGTH
= 1760 Yards
= 5280 Feet
= 1000 Meters
= 0.6214 Mile
= 1.607 Kilometers
= 0.3048 Meter
= 3.2808 Feet
= 39.37 Inches
= 2.54 Centimeters
= 0.3937 Inches
UNITS OF AREA
1 Square Mile
= 640 Acres
= 2.5899 Square Kilometers
= 1,000,000 Square Meters =
0.3861 Square Mile
= 43,560 Square Feet
= 144 Square Inches =
0.0929 Square Meter
= 6.452 Square Centimeters
= 10.764 Square Feet
= 0.155 Square Inch
UNITS OF VOLUME
1.0 Cubic Foot
= 1728 Cubic Inches
= 7.48 US Gallons
= 1.2 US Gallons
Meter = 35.314 Cubic Feet
= 264.2 US Gallons
= 1000 Cubic Centimeters
= 0.2642 US Gallons
UNITS OF WEIGHT
1.0 Metric Ton
= 1000 Kilograms
= 2204.6 Pounds
= 1000 Grams
= 2.2046 Pounds
1.0 Short Ton
= 2000 Pounds
UNITS OF PRESSURE
1.0 Pound per
square inch = 144 Pound per
1.0 Pound per
square inch = 27.7 Inches of
1.0 Pound per
square inch = 2.31 Feet of
1.0 Pound per
square inch = 2.042 Inches of
= 14.7 Pounds per square
= 33.95 Feet of water*
1.0 Foot of water =
0.433 PSI = 62.355 Pounds per
1.0 Kilogram per
square centimeter = 14.223 Pounds per
1.0 Pound per
square inch = 0.0703 Kilogram
UNITS OF POWER
(English) = 746 Watt
= 0.746 Kilowatt (KW)
(English) = 550 Foot pounds
1.0 Horsepower (English)
= 33,000 Foot pounds per minute
(KW) = 1000 watt
= 1.34 Horsepower (HP) English
(English) = 1.0139 Metric
1.0 Metric horsepower
= 75 Meter X Kilogram/Second
horsepower = 0.736
Kilowatt = 736 Watt
(*) At 62 degrees Fahrenheit (16.6 degrees Celsius).
This Appendix provides a guide to making the necessary
for a detailed site analysis.
Measuring Gross Head
Measuring Head Losses
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
5. Describe water
condition (clear, muddy, sandy,
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
9. Approximate depth
of the pond in feet (or
10. Distance from
power plant to where electricity
will be used in
feet (or meters).
distance from dam to power plant.
12. Minimum air
13. Maximum air
14. Estimate power
to be used.
15. ATTACH SITE
SKETCH WITH ELEVATIONS, OR TOPOGRAPHICAL
MAP WITH SITE
The following questions cover information which, although
necessary in starting to plan a water power site, will
be needed later. If
it can possibly be given early in the project,
this will save time later.
Give the type, power, and speed of the
machinery to be
indicate whether direct, belt, or gear drive is
For electric current, indicate whether
direct current is
alternating current is required. Give
number of phases and frequency.
Say whether manual flow regulation can be
used (with DC
and very small
AC plants) or if regulation by an automatic
MEASURING GROSS HEAD
Method No. 1
Surveyor's leveling instrument--consists of
parallel to a telescopic sight.
Scale--use wooden board approximately 12 ft
Surveyor's level on a tripod is placed
reservoir dam on which the headwater level is
After taking a reading, the level is turned
180[degrees] in a
circle. The scale is placed downstream
at a suitable
distance and a second reading is taken.
is repeated until the tailwater level is
<MEASURING HEAD WITH SURVEYOR'S LEVEL>
Method No. 2
This method is fully reliable, but is more tedious than
No. 1 and need only
be used when a surveyor's level is not
Board and wooden plug
Ordinary carpenter's level
Place board horizontally at headwater level
level on top
of it for accurate leveling. At the
end of the
horizontal board, the distance to a
set into the ground is measured with a scale.
The process is repeated step by step until
<MEASURING HEAD WITH CARPENTER'S LEVEL>
Flow measurements should take place at the season of lowest
flow in order to guarantee full power at all times.
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
streams or sources of power would then offer a
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
hole" created by a natural dam.
Channel the water into a pipe
and catch it in a bucket of known capacity.
stream flow by measuring the time it takes to fill the
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 on the
side. A small pond
is formed upstream from the weir. When
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. Use a
carpenter's level to be sure the second board is
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
the flow from Table 1 on page 56.
VALUE (Cubic Feet/Second)
Overflow Height 3
feet 4 feet
5 feet 6 feet
8 feet 9 feet
Method No. 3
The float method is used for larger streams.
Although it is not
as accurate as the previous two methods, it is adequate for
Choose a point in the stream where the bed
is smooth and the cross section is fairly uniform for a
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
In this way, the cross-sectional area of the stream is
use the following formula to calculate the flow:
"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.
Open Channel Head Losses
The headrace and the tailrace in the illustration above are
open channels for transporting water at low velocities.
walls of channels made of timber, masonry, concrete, or
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.
The head loss in open channels is given in the
friction effect of the material of construction is called
Various values of "N" and the maximum water
which the walls of a channel will not erode are given.
Channel Wall (feet/second)
Value of "n"
0.033 (Jagged) 0.045
sandy water 10.0
clean water 20.0
Sandy loam, 40%
soil, 65% clay
with rubble sides
The hydraulic radius is equal to a quarter of the channel
width, except for earth-walled channels where it is 0.31
the width at the bottom.
To use the nomograph, a straight line is drawn from the
of "n" through the flow velocity to the reference
point on the reference line is connected to the hydraulic
radius and this line is extended to the head-loss scale
also determines the required slope of the channel.
Using a Nomograph
After carefully determining the water power site
in terms of water flow and head, the nomograph is used to
* The width/depth of
the channel needed to bring the water to
of the water turbine.
* The amount of head
lost in doing this.
To use the graph, draw a straight line from the value of
through the flow velocity through the reference line tending
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
hr 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
If the channel is made of earth, the bottom width of the
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
the graph, the optimum hydraulic radius would be
2 feet--or for a wood channel, a width of 8 feet.
wood channel of this dimension would be prohibitively
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
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
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 Head Loss and Penstock Intake
The trashrack consists of a number of vertical bars welded
an angle iron at the top and a bar at the bottom (see Figure
below). 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
into which a timber gate can be inserted for shutting off
the flow of water to the turbine.
(See shut-off caution on page
The penstock can be constructed
from commercial pipe. The
must be large enough to keep the head loss small.
pipe size is determined from the nomograph.
A straight line
drawn through the water velocity and flow rate scales gives
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
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
choice of pipe material and the method of making the pipe
depend on the cost and availability of labor and the
SMALL DAM CONSTRUCTION
Concrete and Masonry Dams
This appendix is not designed to be exhaustive; it is meant
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
expert, or even several; for example, engineers for their
savvy and an environmentalist or concerned agriculturalist
for a view of the impact of damming.
An earth dam may be desirable where concrete is expensive
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 over the crest of an earth
water is held satisfactorily by earth but moving water is
The earth will be worn away and the dam destroyed.
The spillway must be lined with boards or concrete to
seepage and erosion.
The crest of the dam may be just wide
enough for a footpath or may be wide enough for a roadway,
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
One way of preventing seepage is to blast and clean out a
series of ditches, or keys, in the rock, with each ditch
a foot deep and two feet wide extending under the length of
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.
downstream side should consist of lighter and more porous
which drains quickly and thus makes the dam more stable than
it were made entirely of clay.
The crib dam is very economical where lumber is easily
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
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
planks are used as an apron to guide the
water that overflows the dam back into the stream bed.
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
with impervious material such as clay or heavy earth and
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.
They also anchor the
If the dam rests on rock, priming planks cannot and need not
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 lower ends of the priming planks are pointed as shown in
the Figure on page 69 and must be placed one after the other
shown. Thus each
successive plank is forced, by the act of
driving it, closer against the preceding plank, resulting in
solid wall. Any
rough lumber may be used. Chestnut and
considered to be the best material.
The lumber must be free
from sap, and its size should be approximately 2" X
In order to drive the priming planks, considerable force may
required. A simple
pile driver will serve the purpose. The
Figure below shows an excellent example of a pile driver.
AND MASONRY DAMS
Concrete and masonry dams more than 12 feet high should not
built without the advice of an engineer with experience in
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
feet in height. It
is made of rough stones. The layers
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
Small concrete dams should have a base with a thickness 50
percent greater than height.
The apron is designed to turn the
flow slightly upwards to dissipate the energy of the water
protect the downstream bed from erosion.
<SMALL CONCRETE DAM>
DECISION MAKING WORKSHEET
If you are using this as a guide for using the Michell
Turbine in a development effort, collect as much information
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
Volunteers in Technical Assistance
Wilson Boulevard, Suite 500
Arlington, Virginia 22209, USA
CURRENT USE AND AVAILABILITY
* Describe current
agricultural and domestic practices which
water. What are the sources of water
and how are
* What water power
sources are available? Are they small
Large but slow-flowing?
* What is water used
* Is water harnessed
to provide power for any purpose? If
what and with what
positive or negative results?
* Are there dams
already built in the area? If so, what
been the effects
of the damming? Note particularly any
sediment carried by the water--too much sediment
can create a
* If water resources
are not now harnessed, what seem to be
factors? Does cost seem
prohibitive? Does the
lack of knowledge
of water power 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
machines such as grinders, saws, pumps?
* Given available
water power sources, which ones seem to be
available and most
useful? For example, one stream which
runs quickly year
around and is located near the center of
activity may be the only feasible source to tap
* Define water power
sites in terms of their inherent potential
for power generation.
* Are materials for
constructing water power technologies
locally? Are local skills
sufficient? Some water
demand a rather high degree of construction
* What kinds of
skills are available locally to assist with
maintenance? How much skill is
and maintenance? Do you need to train
Can you meet the following needs?
Some aspects of the Michell turbine require
metalworking and/or welding.
Estimated labor time for full-time workers
40 hours skilled labor
40 hours unskilled labor
8 hours welding
* Do a cost estimate
of the labor, parts, and materials
* How will the
project be funded?
* What is your
schedule? Are you aware of holidays and
harvesting seasons which may affect timing?
* How will you
arrange to spread information on and promote
use of the
* Is more than one
water power technology applicable?
to look at all the
costs. While one technology appears to
expensive in the beginning, it could work out to
be less expensive
after all costs are weighed.
* Are there choices
to be made between a waterwheel and a
example, to provide power for grinding grain?
Again weigh all
the costs: economics of tools and
maintenance, social and cultural dilemmas.
* Are there local
skilled resources to introduce water power
Dam building and turbine construction should
carefully before beginning work.
higher degree of
skill required in turbine manufacture (as
waterwheel construction), these water power
to be more expensive.
* Where the need is
sufficient and resources are available,
manufactured turbine and a group effort to build
the dam and
install the turbine.
* Is there a possibility
of providing a basis for small
* How was the final
decision reached to go ahead--or not go
RECORD KEEPING WORKSHEET
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
This kind of detail can often be monitored
most easily in charts (such as the one below).
Cost Per Item
Some other things to record include:
* Specification of
materials used in construction.
* Adaptations or
changes made in design to fit local
* Equipment costs.
* Time spent in
construction--include volunteer time as well
as paid labor;
full- or part-time.
shortage, work stoppage, training difficulties,
shortage, terrain, transport.
Keep log of operations for at least the first six weeks,
periodically for several days every few months.
This log will
vary with the technology, but should include full
outputs, duration of operation, training of operators, etc.
Include special problems that may come up--a damper that
close, gear that won't catch, procedures that don't seem to
make sense to workers, etc.
Maintenance records enable keeping track of where breakdowns
occur most frequently and may suggest areas for improvement
strengthening weakness in the design.
records will give a good idea of how well the project is
working out by accurately recording how much of the time it
working and how often it breaks down.
records should be kept for a minimum of six months to one
after the project goes into operation.
Hours & Date
Totals (by week or month)
Totals (by week or month)
This category includes damage caused by weather, natural
vandalism, etc. Pattern the records after the routine
Describe for each separate incident:
* Cause and extent
* Labor costs of
repair (like maintenance account).
* Material costs of
repair (like maintenance account).
* Measures taken to