Manual of experiences ans tolerances in rope pump production
C.a. THE CRANK
The function of the crank is to turn the wheel by means of power applied by the user.
It consists of an axle with two 90-degree bends. The crank or axle is made of ¾" pipe,
which is black pipe for the family and extra-strong pumps and galvanized pipe for the
community pump. The diameter of this pipe is 27 millimeters, while the thickness of the
material is 2.0 millimeters. It is possible to use 1/2" pipe for the crank, but it is
not recommended. The 1/2" pipes were the weakest part of the family pump after several
years of use. The difference in price between 1/2" and 3/4" pipe is not that large, which
has led to the use of 3/4" pipe in all designs.
On pages 56 and 60 of the photo-manual is a photo of a relatively rustic pipe bender.
The channel in the bender pulleys should have the same or slightly smaller width than the
diameter of the pipe and a slightly larger depth in the middle of the diameter of the pipe.
The bend can be made in either of two ways: by holding the pipe and stretching it at the bend,
or by letting the pipe slide slightly until the fixed pulley rotates also, which produces better
results in the bend. However, the method to be used depends on the material used or available.
Pipe made of a relatively soft material and which has a smaller thickness will bend more
easily without stretching the material, whereas more rigid pipe tends to wrinkle inside the
turn and should be stretched while bending. The minimum thickness of the material used to
make the pipe is 1.9 mm.
The bender's pulleys have an minimum inside diameter of 11.5 cm, which is also twice the
size of the inside radius of the bends on the crank.
The radius or distance between the axle and the handle of the crank is 33.5 cm (see
C-GENERAL-05 in the drawing manual). This radius is large for children doing the pumping
but is necessary in order to exert the maximum force related to the weight of the water
column, which has a maximum of 10 kilograms. The radius can be a little smaller for adults
because of their strength or larger because of the length of their arms. This maximum
strength also depends on the depth of the well in which the pump is being used.
An important detail is the first bend at the axle. Care must be taken to ensure that
the bend begins past the bushing. Beginning the bend right at the bushing will wear
the axle causing it to break.
The roller and the handle are 15 centimeters in length, long enough for two children's
hands or one adult hand. The spacers on the handle are made of the same pipe as the
handle without any space between them so as to avoid the hand getting caught between the
handle and spacers. Experience has shown that despite their short life span, PVC can be
used and replaced by opening the pipe lengthwise. There may be a need to seek alternatives
for the bushings and handle should the pipe not be available on the market. These should
fit snuggly around the axle pipe. Bushings can also be made of iron strip.
As indicated in the drawings, the angle of the bends is 90o, although they can be a
little wider causing the handle to be further from the wheel structure, making the distance
or radius between the axle and handle decrease slightly, which should be corrected.
At the same time there is an increase in the distance between the handle and the wheel
structure. This distance between the handle and the structure is important when installing
the pump. The rope must be able to descend freely into the well without touching the wall,
therefore the pump should be as centered as possible on the well. On the other side, the
handle should remain outside the well wall so as to make the pumping process as
comfortable as possible. Depending on the infrastructure of the well and the thickness
of the well wall, it may be advisable to leave the handle farther from the structure
using a less pronounced bend. This situation, of course, depends on the local customs
regarding the production of well walls.
Depending on the depth of the wells, pumps with one or two handles are used. Pumps with
two handles are used to increase power and the work becomes social for users.
Pumps used for 0 - 37-meter depths require one handle.
From 37 - 50 meters, special pumps with wooden bearings and double handles are used.
MATERIALS FOR THE CRANK
| Quantity | Material | Measurement | Section |
|---|
| 1 | Black pipe | 3/4" x 100 cm | Shaft |
| 1 | Galvanized pipe | 1" x 15 cm | Roller |
| 2 | Galvanized pipe | 1" x 1 cm | Spacer |
TECHNOLOGICAL ALTERNATIVES.
In several parts of the world, including Nicaragua galvanized pipe with a screw-thread
and elbows were used to build the crank (Axle with handle). The result has always been
negative, as the pipe screwed into the elbow, in the end always cracks as it cannot
resist the alternate forces occurring in pump operation.
The use of solid axles was reported in some countries (i.e. Zimbabwe) but had no real
raison d'être.
Instead of the bend, a pipe can be cut at a 45o angle then resoldered in order to
obtain a 90o angle. This is more work and as long as 3/4" pipe is used, there should
be no problems.
Connected with this are the rustic rope pump designs in which the axle must cover the
entire space between two posts on both sides of the well. The length of the axle, the
momentum involved, as well as the modular forces received by the axle make it difficult
to predict its long range behavior, especially when soldering is used to fasten the
wheel. In Nicaragua and El Salvador, experimental tests are being carried out with axles
made from 1" pipe. This pipe can work in these designs when the distance between the
posts is not extremely long, while it would be worth considering using axles made from
1 ¼" or 1 ½" pipe to provide a long term solution.
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