Equipping a borehole

106  Download (0)

Full text

(1)
(2)

Equipping a Borehole

First English Edition. January 2011.

(3)

Equipping a Borehole

First English Edition. January 2011. ISBN: 978-84-614-0533-6

© Santiago Arnalich Castañeda

All rights reserved. This manual can be photocopied for personal use if your economic situation does not allow you to buy a copy. Otherwise, please consider buying one to support this kind of initiative.

If you want to reproduce part of the contents of this book, contact us at the following email: publicaciones@arnalich.com

Cover photo: Borehole cap protection, Wazir Abad, Afghanistan.

Translation: Oliver Style.



DISCLAIMER: The information contained in this book has been obtained from credible and internationally respected sources. However, neither Arnalich nor the author can guarantee the precision of the information published here and are not responsible for any errors, omissions, or damage caused by the use of this information. It is understood that the information published herein is without a specific purpose and under no circumstances intends to provide professional engineering services. If these services are required, the assistance of a qualified professional is necessary.

(4)

Index

1. Introduction 1

1.1 About this book ... .1

1.2 What is a borehole? ... .

1.3 Information to gather ... .4

2

1.4 Chronology of an installation ... .4

1.5 Adapting to the context ... .5

2. Viability

7

2.1 Water testing ... .7

2.2 Interpreting a pumping test ... .8

2.3 Approximate calculation of operating costs ... 10

2.4 How to abandon a borehole

... 12

3. Pumping 15

3.1 What happens in the aquifer when you pump? ... 15

3.2 Determining the optimum flow ... 18

3.3 Determining the pumping height ...

3.4 Pump selection ... 21

20

3.5 Pump installation depth ... 24

4. Piping 27

4.1 The rising main ... 27

4.2 Accessories ... 28

4.3 Corrosion potential ...

29

5. Electrical system 33

5.1 Pump cable splice ... 33

5.2 Cable selection ...

5.3 Level sensors ... 34

34

5.4 Control panel ... 35

5.5 Ground connection ... 36

(5)

www.arnalich.com Helping improve humanitarian impact through training and consultancy.

6. Energy 39

6.1 Selecting a generator ... 39

6.2 Connecting to an existing electrical grid ... 41

6.3 Mono pumps ...

42

7. Ordering materials 43

7.1 Rules for the purchasing process ... 43

7.2 The importance of communication ...

7.3 Ordering with precision ... 45

44

7.4 Critical material ...

7.5 Dividing up orders ... 50

49

7.6 Quality ...

50

8. The installation 53

8.1 Lowering the pump ... 53

8.2 Other installations ...

8.3 Tools, materials, and labour ... 58

58

8.4 Operation problems ... 60

9. Protection 61

9.1 Seal ... 61

9.2 Fencing ...

9.3 Pump house ... 61

61

9.4 Low-cost boreholes ... 64

Bibliography ... 65

About the author ... 67

APPENDICES 69

A Information gathering checklist ... 71

B Physicochemical limits in drinking water ... 72

C Material and tools checklist ... 74

D Minimum generator sizes ...

E Flow measurement with the V-notched weir ... 76

75

F Bowline knots ... 79

(6)
(7)
(8)

1. Introduction

1. 1 ABOUT THIS BOOK

This book is intended to provide you with the tools you need to get a borehole up and running, following drilling, in a Development Cooperation context. You´re probably dealing with a real-life situation and don´t have time to do exhaustive research to get up to scratch. The book is intended to be:

99 % fat free. No meticulous explanations or interminable examples. Only what´s really needed is included.

Simple. One of the common causes of failure is that complexity and excessive rigour become intimidating and things are left undone. At the risk of causing offence, the explications take nothing for granted.

Chronological. It roughly follows the logical order you´d do things in.

Practical. With numerous calculation examples.

Self-contained. It´s assumed you are in a remote area without easy access to information, so the essential things you need to know are all here. Nonetheless, links to additional information are provided.

The practical aspects of the installation are left in the hands of the technicians. Although boreholes can be equipped with manual pumps, solar, wind powered, or vertical mechanical pumps, only submersible electrical pumps are dealt with here.

(9)

www.arnalich.com Helping improve humanitarian impact through training and consultancy. If you´re reading this book, drilling the borehole has probably already taken place and after the drilling company has gone, you´re left with something that looks like this:

Fig. 1.1. Borehole head after drilling and testing, Mudug, Somalia.

This book deals with all the necessary stages to get from here to a fully operating borehole, ready to hand over to the community.

1. 2 WHAT IS A BOREHOLE?

When it rains, rainwater filters through the ground, descending by the force of gravity until it reaches a layer of limited permeability, generally clays or bedrock. The result is an enormous underground lake, an aquifer. The borehole is a pipe installed vertically which allows access to the aquifer.

(10)

© Santiago Arnalich Arnalich. Water and habitat www.arnalich.com The pipe or well casing also prevents the borehole from collapsing after drilling. At the point where it enters the aquifer, it is perforated to allow water to enter. These sections of perforated pipe are called well screens and are surrounded by gravel, which acts as a roughing filter and allows the water from the aquifer to enter more effectively. A submersible pump is placed inside the well casing, suspended from another smaller pipe, the rising main. The rising main allows the water to be pumped out of the borehole, where it can be connected to a distribution system.

(11)

www.arnalich.com Helping improve humanitarian impact through training and consultancy.

1. 3 INFORMATION TO GATHER

Whether you are rehabilitating an old borehole or drilling a new one, you will need to have the following information available:

1. A pump test. This will let you calculate the flow rate which the borehole is capable of delivering and the pumping depth.

2. The construction details of the borehole. The diameter dictates the maximum size of the pump that will fit, allowing sufficient space for cooling. Since the pump is installed inside a section of casing, the space between the casing and screen determine where it can be installed. Finally, the depth of the first screen determines the maximum drawdown level before it is left uncovered.

3. A water test to determine water quality and anticipate corrosion.

4. Access to energy. The nearest electrical supply point, if there is one, and the tension. If a generator is required, it needs to be adequately housed.

5. The technical operating conditions. The power of the pump will depend, among other things, on the length of the rising main and the pumping elevation.

6. The organisational operating conditions. This will determine the need to provide accommodation for an operator or guard.

7. Country regulations.

Appendix A contains a checklist of the information to gather.

1. 4 CHRONOLOGY OF AN INSTALLATION

If the distribution system that the borehole supplies is already built, you´re probably already under a bit of pressure to get the borehole up and running as soon as possible. To do so, it´s essential to build the pump house while the materials are being ordered. If there is still no system to connect to, you can take things a little more slowly.

(12)

© Santiago Arnalich Arnalich. Water and habitat www.arnalich.com 1. Viability study. The water is tested to determine whether it´s apt for the

given situation and that the operation of the borehole is economically viable. Deep boreholes with low flow are unfavourable. Section 2.3 describes how to determine the operating costs so you can be sure they are within acceptable limits, which end users are able to pay for.

2. Pump selection and design. The pump will determine the size of the pipes and the electrical components. Once the pump is selected all the required components can be ordered. While they are being delivered, the pump house can be built. Order the pump and the generator (if required) as soon as possible. Depending on their size and where you are, this can take several months.

3. Construction of the pump house. To protect the components from the elements, interference or theft, a pump house must be built, preferably before the installation. Once you know whether the pump house has to house a generator, operator, or serve as a local warehouse, find a design and prepare a construction contract. If there is a local water or pump housing authority in the region that fits the bill, use their design. Find out if there are local regulations you need to abide by.

4. Installation and service test. Following the installation, perform an operating test and check the performance: flow, pressure, and energy consumption.

On the following page a flow diagram shows the installation process.

Solar pumping is very competitive for small systems. As a rule of thumb (although it changes with different circumstances and will change over time), consider a solar pumping system when the power of the pump is below 1 kW. These systems exceed the purpose of this book. You can learn more about solar pumping in another of our books: www.arnalich.com/en/books.html

1. 5 ADAPTING TO THE CONTEXT

This book looks at the general approach for this kind of project, focusing on the technical aspects. Nonetheless, the political and social aspects are decisive and can vary hugely. In development contexts, each place is distinct. If you want to avoid problems, make sure you respect the local procedures which are common in the area, and that you work together with the local water authority.

(13)
(14)

2. Viability

Equipping a borehole that´s not viable implies a considerable financial outlay and is potentially dangerous for the population. This chapter will help you decide between equipping and closing off. To do this, you will need the results of a complete water analysis and a pumping test.

2. 1 WATER TESTING

Organise the most complete water analysis locally available, using an official laboratory which is suitably competent. Together with the analysis itself, you will be provided with an official certificate detailing the composition of the water. Generally, it´s not a good idea to trust those done by the drilling companies themselves, as they are not official analysis and hide vested interests to avoid problems with the work being undertaken.

Collecting samples

It´s important to collect a sufficient quantity of water so that the laboratory can do the analysis. One and a half litres is usually sufficient. A mineral water bottle is the ideal container to use. Avoid using old or metal containers to collect the sample. Either way, consult with the laboratory as to the required quantity and transport conditions.

The most opportune moment to take a sample is after the pumping test. Samples taken during the development of the borehole are affected by the drilling process. Boreholes in which cement has been used recently can give high pH and water hardness values.

(15)

www.arnalich.com Helping improve humanitarian impact through training and consultancy. In the case of a borehole that has been rehabilitated and that has not been used for some time, it´s best to install a pump and let the water flow for several hours before taking the sample.

Results

Appendix B contains a summary of the basic parameters and their maximum values as recommended by the World Health Organisation. You can also follow the link to the WHO website to check the values for other substances and find out about their health effects, their effect on materials and treatment possibilities.

If one of the parameters is beyond the recommended range, there are 4 possibilities: • The relevant water or health authority considers that the expected benefits

outweigh the possible negative side-effects and water use is authorised. • That a viable treatment system is available. Always consider the possibility of

treatment by dilution, which consists of mixing water from two different sources, so that the mixture meets the required values.

• Find an alternative use. For example, boreholes which produce water that is too saline for human use can be used for livestock (notably goats and camels) or for the growing of crops which are tolerant to saline water.

• Close off the borehole and find another alternative. Closing a borehole in a safe way is very important, so that it doesn´t become an entry point for contamination into the aquifer. This process is described in section 2.4.

The water from a borehole should not be turbid. Turbidity of over 5 NTU indicates that the borehole has not been properly developed or that there are construction defects.

2. 2 INTERPRETING A PUMPING TEST

A pumping test looks at the evolution of the water level in a borehole which is pumped at a constant flow. There are many ways of documenting them, but they all contain a recommended pumping flow rate and a measurement of the drawdown at that flow.

Can it be trusted?

The details of performing a test go beyond the scope of this book, but pay attention to the following points so as to make sure it can be trusted:

(16)

© Santiago Arnalich Arnalich. Water and habitat www.arnalich.com • Pumping tests should be done over a long period, at least 24 hours, except

in special circumstances (curfews, risks, etc.).

• The pumping flow should be constant. There can be no interruptions (except those that are planned as part of a staged test) or changes in the pumping flow.

• It´s common that drilling companies develop the borehole at the same time as doing the pumping test, to cut costs. Seeing as the objective of

developing the borehole is to clean out the remains from the drilling process to increase the borehole flow, these kinds of pumping tests are not what they should be.

• They cannot be done with a compressor. The compressed air method is a development technique without a constant flow.

• It´s best to be present in person to check that everything is being done as it should and that the contracted company do not exaggerate or falsify the results to avoid problems.

Is the flow sufficient?

At this stage, we just want to check that the borehole flow is sufficient for our needs. The pumping test specifies the maximum exploitable flow. As a general rule, if this flow is sufficient to meet the daily needs of the population with:

Less than 14 hours in operation, you can continue with the installation without further analysis.

Between 14 and 18 hours, bear in mind that the borehole may become too small in the near future due to population growth or reduced water levels in the aquifer due to prolonged exploitation. Furthermore, using the borehole becomes more expensive for the population.

Over 18 hours. The borehole does not meet the needs of the population. Depending on the circumstances, you can decide whether or not to equip the borehole immediately or wait for a second borehole. If the second borehole has sufficient flow the first need not be installed. If it doesn´t, a combined installation can be planned.

Section 3.2 shows the minimum demand values which can be used to work out the needs of the population.

(17)

www.arnalich.com Helping improve humanitarian impact through training and consultancy.

2. 3 APPROXIMATE CALCULATION OF OPERATING COST

Despite delivering water of excellent quality in adequate quantities, it is possible that the operating costs of a borehole are beyond the reach of the population. This is generally the case for very deep boreholes.

The main expense derives from energy consumption, which is often far higher than material, treatment or personnel costs. Therefore, to determine whether the population is able to pay for the operating costs of the borehole, calculating the energy consumption cost is usually sufficient.

The energy consumed in the operation of a borehole in kWh per day is:

𝑒𝑒 =3,6 ∗ 10𝑚𝑚𝑚𝑚ℎ6 𝜂𝜂

Where: m, mass of water per day in kg (1 litre of water weighs 1 kg)

h, the pumping height taken from the lowest drawdown point to the water surface at the point of delivery. If the system is operated under pressure (i.e. pumps directly into a pressurized distribution network) add 10 meters for every bar of pressure.

g, 9.8 m/s2 Calculation example:

A borehole has been drilled for a semi-urban population of 8000 people. The pumping test reveals that the maximum capacity of the borehole is 11 l/s. Is this enough to meet the needs of the population assuming 100 litres per person per day?

With a daily demand of 100 litres per person, the quantity of water consumed is:

8,000 people * 100 l/person*day = 800,000 litres daily demand.

The hourly production is: 11 l/s * 3600 s/hour = 39,600 l/h

The required number of operating hours is:

800,000 l / 39,600 l/h = 20.2 hours

(18)

© Santiago Arnalich Arnalich. Water and habitat www.arnalich.com η, total efficiency (wire to water). For a correctly selected pump, this is around 60%. To take into account frictional losses in the pipes use a value of 0.5 (50%). That way you´ll avoid having to work out frictional losses for now.

The operating cost is calculated using the local electricity tariff. As generators are frequently required, you need to know the unit fuel cost of diesel. The average fuel consumption of a generator is 0.3 litres of diesel per kWh produced.

Ability to pay

To work out what the community is able to pay, the simplest is to look at what they already pay for existing services:

𝑒𝑒 =3.6 ∗ 10𝑚𝑚𝑚𝑚ℎ6 𝜂𝜂 =60,000𝑘𝑘𝑚𝑚 ∗ 79𝑚𝑚 ∗ 9.8𝑚𝑚/𝑠𝑠3.6 ∗ 106 ∗ 0.5 2= 25.8 𝑘𝑘𝑘𝑘ℎ Calculation example:

A borehole powered by a generator pumps 60,000 litres per day, to a tank with the overflow situated at an elevation of 35m. The dynamic height of the borehole is 44m and the cost of diesel is €1.03/l. How much will it cost to pump per day?

The pumping height is 35m + 44m = 79m. The energy consumed is:

The number of litres of diesel required is:

25.8 kWh * 0.3 l diesel/kWh = 7.74 litres

(19)

www.arnalich.com Helping improve humanitarian impact through training and consultancy. Then, meet with the end-users and discuss what they can and can´t pay. Remember this is not your decision...just as it´s none of their business whether or not you spend your salary on cat vitamins or hair tonic!

2. 4 HOW TO ABANDON A BOREHOLE

If you´re unlucky and the borehole isn´t viable, you´ll have to abandon it. It´s especially important to close off a borehole in a safe way. The objectives of well abandonment are:

1. Avoiding accidents with animals or children tripping or falling.

2. Avoiding the contamination of the aquifer. The borehole is an easy point of entry for any kind of contamination. Without the borehole, water has to pass through several meters of subsoil before reaching the water table. It´s filtered on its way down. Contaminated water can reach the aquifer directly via the borehole in large quantities and quickly. This also applies to dry boreholes.

3. Allowing for re-use if needed. A low-flow anti-economic borehole can be useful as a backup when the main source is out of action.

If the well casing is made of steel, the cheapest and most direct way is to weld on an end cap and build a cement platform with a 2 meter radius, sloped to the outside edge.

In boreholes cased with PVC, the platform is built up around the pipe, to form a reinforced concrete box with a lid. The slab which serves as the lid needs to be sufficiently heavy to avoid manipulation:

(20)

© Santiago Arnalich Arnalich. Water and habitat www.arnalich.com The sanitary seal is part of the correct construction process of a borehole. If there is none, it´s best to seal at least a few meters down with cement grout or bentonite.

If future use of the borehole has been discarded, another objective needs to be met: avoiding water from a horizontal stratum reaching another via the borehole. In this case, the borehole is backfilled with material similar to that which was extracted during drilling. Pay special attention not to fill the borehole with materials that can be a source of contamination.

(21)
(22)

3. Pumping

Once you have decided that the borehole is viable, the next step is to select the pump, and with this, size the remaining components to put it into service. The correct choice of pump is essential for the economics of the borehole.

3. 1 WHAT HAPPENS IN THE AQUIFER DURING PUMPING?

An aquifer at rest has a roughly horizontal surface. The depth at which the water is found, measured from the borehole upper end, is called the static level. When water is pumped from a borehole, a depression in the form of a cone is formed in the centre of the borehole, similar to a whirlpool in a plug hole. The water level drops noticeably down to a new level, the dynamic level. The form of the cone depends on the flow rate. At higher flow rates, the depression cone is more abrupt and the vortex is lower. The difference in height between the static and dynamic levels is known as the drawdown.

The difference between the static level and the dynamic level allows a preliminary approximation of the capacity of the borehole. The most productive boreholes are those in which the cone forms very slowly. Large flows are required to separate the static from the dynamic level.

(23)

www.arnalich.com Helping improve humanitarian impact through training and consultancy.

Yield vs. drawdown curve

The maximum drawdown a borehole can tolerate is generally a few meters above the first filter. However, it´s uneconomic to pump a borehole to its maximum capacity. As the pumping rate increases the water level drops, and this means that all the water pumped from the borehole has to be pumped from a lower level, with higher pumping costs. It´s very important not to confuse the maximum pumping flow with the optimum pumping flow.

To decide on the operating flow you need a curve which relates the flow to the drawdown it produces. These curves can be found in the pumping test report and they are similar to the one shown below:

(24)

© Santiago Arnalich Arnalich. Water and habitat www.arnalich.com

Fig. 3.1. Example of a flow curve vs. drawdown.

First of all, note that if you are pumping at, for example, 8 m3/h, you are doing so at a depth of 5 meters with respect to the static level. According to what appears in section 2.3, and assuming a daily operating time of 8 hours, €196.7 of diesel is required annually for this pumping range. If exactly the same amount of water is pumped at 20m3/h, it is pumped from a depth of 45m, at an annual cost of €1,768, almost ten times as much. The conclusion is obvious: pump at the lowest reasonable rate!

Secondly, note that if the pumping test is not done in stages, the curve tends to have an inflection point, understood as the point at which it begins to fall more sharply.

The difference in pumping height between 0 and 6 m3/h is only 5 m. The difference in height between pumping 8 and 8.8 m3/h is more than 30m. To obtain 800 litres more water (10%) the energy consumption has increased 250% times:

Moving down along the points of inflection is going to end up being expensive!

(25)

www.arnalich.com Helping improve humanitarian impact through training and consultancy. Pumping at lower rates will also allow you to reduce the pipe size through which the water will flow.

3. 2 DETERMINING THE OPTIMUM FLOW

The optimum flow is not the maximum operating flow. Nevertheless, a lack of investment is often the reason why boreholes are working at their maximum capacity. This implies an added cost to end-users, as we´ve just seen.

The importance of the tank

To avoid premature damage to a pump, the number of on and off cycles must be limited. On the other hand, submersible pumps work on an all-or-nothing basis: they can´t be run at varying flow rates to meet the population´s needs. This means a reservoir tank is required to cushion the variations in demand over the course of the day and avoid the pump being turned on and off continually.

The pump is selected in such a way as to minimise the size of the tank (reduced investment costs) and minimise the pumping depth (reduce operating costs). The goal is to reduce the overall cost.

The procedure consists of putting together a daily demand pattern and from there sizing the tank-pump pair. Then, the total cost of each pump-tank pair is compared. The theory behind this and calculation examples can be found in Gravity Flow Water Supply available at www.arnalich.com/en/books.html.

Quick start procedure for choosing the flow rate

If you were getting worried, here comes the good news. Most populations can be worked out using the following approximation:

1. Calculate the total daily demand of the population. 2. Divide it by 24 to obtain the average hourly flow rate.

3. Multiply this figure by a factor of 1.8 to work out the pump flow rate. 4. Check that the end result is to the left of the point of inflection.

(26)

© Santiago Arnalich Arnalich. Water and habitat www.arnalich.com This approximation provides good pumping economy and near optimal tank size, ensuring that the pump is only turned on a few times a day. This procedure does not work for raised tanks, pneumatic tanks, or highly variable water use.

You don´t need to work out future demand projections for the population. Pumps only last for a few years. Nonetheless, remember that the calculation must be repeated when the pump is replaced.

The daily demand depends a lot on the context. Ideally, you´re able to take measurements and talk to the population. If this isn´t possible, you can use these minimum values as a guide:

Minimum daily demand (l/un.)

Urban inhabitant 50 Rural inhabitant 30 Student 5 Outpatient 5 Inpatient 60 Ablution 2

Camel (once a week) 250

Goat and sheep 5

Cow 20

Horses, mules, and donkeys 20

Calculation example:

A borehole has been equipped for a population of 2,580 people. The average family has 40 goats, 2 cows and 6 people. Use the quick start method to work out the optimum pump with the curve in figure 3.1:

The number of families is 2580 / 6 people per family = 430 families.

This means: 430 families * 40 goats per family = 17,200 goats 430 families * 2 cows per family = 860 cows

STEP 1. Using the minimum demand values from the table, the total daily demand is:

2580 people * 30 litres/person*day = 77,400 litres/day 17,200 goats * 5 litres/goats*day = 86,000 litres/day 860 cows * 20 litres/cow*day = 17,200 litres/day

--- 180,600 litres/day

(27)

www.arnalich.com Helping improve humanitarian impact through training and consultancy.

3. 3 DETERMINING THE PUMPING HEIGHT

This is the second parameter we need for determining the required pump.

The total resistance the pump has to overcome is expressed in meters of height is called the pumping head. The forces it has to overcome are:

1. The difference in height between the dynamic water level and the surface where the water is pumped to, the static head. The calculation is done directly subtracting the elevations.

2. The inertia of the water to be moved from rest to the circulating velocity is the velocity head. The average working velocities of water systems are

negligible, so you won’t be considering this one.

3. Friction in the pipes, the frictional head. These are calculated using the frictional loss tables of the given pipe material. The tables and an example of how to use them can be found in Appendix G.

STEP 3. Adjust the flow: 7.5 m3/h * 1.8 = 13.5 m3/h

STEP 4. Figure 3.1 doesn´t have a marked point of inflection as is often the case. Here, the tangents to the curve indicate that this is an intermediate and

(28)

© Santiago Arnalich Arnalich. Water and habitat www.arnalich.com 4. Pumping into a pressurised system requires that the system pressure is

matched, the pressure head. This value is the pressure of the system being fed, knowing that every bar or kg/cm2

The pumping head is the value that is specified on ordering the pump, and is the sum of all of the previous values.

is equivalent to 10 meters.

3. 4 PUMP SELECTION

Once the optimum flow and pumping head are known, the pump selection process is simple. Pumps have a wide operating range, which means it´s not simply a matter of finding a pump that will work, but one that works at optimum efficiency. One

Calculation example:

Work out the pumping height from the previous exercise, knowing that the static level is 20 meters, and that the pump pumps into a tank 36 meters above the borehole entrance, via a PVC pipe 1.2 km long, PN 10, 90 mm in diameter.

The static head is the sum of the drawdown, the static level, and the delivery height to the mouth of the borehole. For 13.5 m3/h the drawdown is 15m (from yield vs drawdown curve).

The static head is: 15m + 20m + 36m = 71m

The frictional loss of the pipes can be read off the tables. 13.5 m3/h corresponds to 3.75 l/s. Reading the J parameter from the tables, the rising main friction loss is negligible and that of the PVC pipe:

For 1.2 km the frictional loss is 7 m/km * 1.2km = 8.4 m.

The total head is 71m + 8.4m = 79.4 m, approximately 80m. The required pump is that which has optimum performance delivering 13.5 m3/h at 80m height.

(29)

www.arnalich.com Helping improve humanitarian impact through training and consultancy. important issue is to make sure the pump fits inside the borehole allowing for cooling (that is leaving 1” on to either side).

Pump characteristic curves

These are curves which define the performance of the pumps. Generally they are grouped into pumps which have the same motor but a varying number of stages.

(30)

© Santiago Arnalich Arnalich. Water and habitat www.arnalich.com To select a pump, the main criterion is efficiency, as there tend to be several pumps which meet the flow requirements and pumping head. This is usually the arching curve in the lower part of the graphs. The process is as follows:

1. Between the curves of different pump models from a variety of manufacturers, look quickly for those that have the desired flow value towards the centre-right area of the graph and discard the rest.

2. In the sheets that remain, trace a vertical line for the optimum flow until it crosses the efficiency line (Eta). Projecting horizontally you find the efficiency (75% in this case). Choose the sheet with the biggest efficiency value.

3. Trace a vertical line for the optimum flow and a horizontal one for the pumping head. The curve closest to the point of intersection is the pump to choose, in this case, it could be the number 9 or 8. Don´t worry if it doesn´t fall exactly on the curve, that is normal. The SP 17-8 pump will deliver a slightly lower flow than 13.5 m3/h (exactly 12 m3/h) and the SP 17-9 a little more (15 m3/h).

(31)

www.arnalich.com Helping improve humanitarian impact through training and consultancy.

Selecting with WebCAPs / WinCAPS

If you´re going to use a pump manufactured by Grundfos (distributed in Africa by Davies and Shirtliff) you can use their software to size the pump very simply. WinCAPs is the version which you can install on your computer and WebCAPs is the same application but over the internet: www.grundfos.com

Select “sizing/selection”, then “groundwater supply”, and follow the instructions.

Fig 3.4b. Screenshot of WebCAPs during pump selection (Grundfos).

3. 5 PUMP INSTALLATION DEPTH

This is the depth at which the pump is installed. A common mistake is to think that the pump should be close to the dynamic water level so that it doesn´t have to pump from a great depth. Pumping water up through water takes no effort, so for practical purposes it makes no difference if you are pumping 5 meters below the water level or 50. To visualise this, imagine a bag of water submerged in a lake. You will only notice it´s weight when you try and raise it out of the water.

Nonetheless, the higher the pump the less pipe and electrical cable you need, and the installation work required is considerably less.

(32)

© Santiago Arnalich Arnalich. Water and habitat www.arnalich.com 1. Installing the pump in a section of well casing. When pumps are installed in a well screen section, small particles enter the pump directly and cause wear.

2. Installing with a section of well screen below, to ensure correct cooling.

3. Leaving a sufficient safety margin so that during seasonal lows in the water table the pump isn´t left dry during pumping periods. Pumping air will quickly burn out your pump. Although they are equipped with level sensors which automatically turn them off, this interrupts the service and multiplies the number of start ups.

(33)
(34)

4. Piping

4. 1 THE RISING MAIN

The rising main connects the pump with the outside world and provides support, as well as carrying the pumped water to the surface. The pump hangs from this pipe. It´s threaded at the bottom and is fixed with a bracket at the top of the borehole, or screwed into an accessory which acts as a lid:

The pipe tends to be made from common galvanised steel in 3 or 6 meter sections, with threaded unions. The diameter should be the same as that of the pump outlet. For the kind of boreholes used in a development context, it´ll probably be 2” to 4”. Only work out the frictional loss for the pipe if it is more than 50m long (see example in section 3.3). This will normally be negligible.

(35)

www.arnalich.com Helping improve humanitarian impact through training and consultancy.

4. 2 ACCESSORIES

These are installed at the entrance of the borehole and control borehole operation.

There are a number ways of joining the accessories. One practical method is that found in the photo above. A ´T´ allows for pumping to the water main (A) or to a washout (B) for testing or cleaning. Following the direction of the flow:

1. 90º elbow. Takes the flow to the horizontal. In the photo a pressure gauge has been installed.

2. Meter. Measures the volume of water which is circulating. It´s installed before the ´T´ to measure the flow through the washout too, when testing. It´s very important that it is installed in the right direction (it comes with a direction of flow arrow).

3. Non-return valve or check valve. This also has an arrow which indicates the direction of flow. It only lets the water pass through in one direction and prevents the water from dropping back down into the borehole once the pump has stopped. Most pumps have one fitted at the pump outlet. This acts as a backup.

4. Tee. Allows for pumping to a washout for tests, and for emptying the main pipe which goes from the accessories to the point of delivery.

(36)

© Santiago Arnalich Arnalich. Water and habitat www.arnalich.com 5. Gate valves. There are two and allow the flow to be opened and closed.

When the main valve is shut and the branch valve is opened, the water is pumped to the washout. If the branch valve is shut and the main one opened, the water continues to the point of delivery.

6. Tap. For taking samples. When an operator is going to be spending some time in the pump house, this is essential.

7. Reduction. This is placed at the end of the line and is in fact an “enlarger” in the direction of flow. The diameter of the rising main tends to be small due to the space limitations within the borehole. Once the pipe leaves the mouth of the borehole, it´s diameter tends to require enlargement. The best point to do this is after all the accessories, as they are much more expensive at larger diameters.

Working out pipe diameters beyond the accessories is not covered here. However, bear in mind that it is not necessarily the same as the pump outlet pipe diameter, and in fact, rarely is.

4. 3 CORROSION POTENTIAL

It´s very important to anticipate whether the water in the aquifer is going to cause corrosion problems. The rising main and the pump are permanently submerged in water and corrosion can wreak havoc.

The problem can be particularly acute in the rising main. Corrosion can weaken the pipe over the course of a few years and can cause the column to fall within the borehole (with some added bad luck, this becomes irreparable).

(37)

www.arnalich.com Helping improve humanitarian impact through training and consultancy. When corrosion is expected, a plastic

pipe must be installed. Pay attention to the fact that corrosion will reduce the diameter.

The photo shows a reduction in diameter due to corrosion (the tuberous effect) in a piece of pipe from a rising main in Eritrea.

Working out the corrosion potential

To work out if the water has encrustive or corrosive characteristics, use the Langelier Index:

IL

=

pHa

-

pHs

=

pHa

-

(

(9.3

+

A

+

B)

-

(C

+

D))

Where:

pHa, pH of the water

A = (Log10 [Total Dissolved Solids] - 1) / 10

B = -13.12 x Log10 (Water temperature in o

C + 273) + 34.55 C = Log10 [Ca2+ in mg/l of CaCO3] – 0.4

D = Log10 [Alkalinity in mg/l CaCO3]

If IL = 0, the water is in chemical equilibrium. If IL < 0, the water has a corrosive tendency. Si IL > 0, the water has an encrusting tendency.

For practical purposes:

If the values are between -0.3 and 0.3, the water won´t give you problems. Between -0.5 and -0.3, there´ll be some corrosion, but nothing too serious. If IL< -0.5, corrosion will be a problem.

If IL > 0.5, there will be major deposits.

To make the calculation less confusing, you can use an online calculator, for example:

(38)

© Santiago Arnalich Arnalich. Water and habitat www.arnalich.com Calculation example:

The water test from a borehole shows the following results: pH = 6.7; TDS= 46 mg/l; Alkalinity = 192 mg/l; Hardness CaCO3 =102 mg/l. If the water is at 12ºC what

precautions should be taken?

The Langelier Index is used to work out whether the water is encrustive or corrosive: A = (Log10 [TDS] – 1)/ 10 = (Log10 [46] – 1)/ 10= 0.066 B = -13.12Log10 (To + 273) + 34.55 = -13.12Log10 (285) +34.55= 2.34 C = Log10 [Ca 2+ in mg/l of CaCO3] – 0.4 = Log10 [102] – 0.4 = 1.6

D = Log10 [Alkalinity in mg/l CaCO3 = Log10 [192]= 2.28

IL = pHa-((9.3+A+B)-(C+D)) =6.7-((9.3+0.066+2.34)-(1.6+2.28)) = -1.1

The water is highly corrosive. Pipes resistant to corrosion should be used, PVC or high density polyethylene (HDPE).

(39)
(40)

5. Electrical system

5. 1 PUMP-CABLE SPLICE

Normally, the pump comes with around a meter of cable for connecting, via another cable, to the control panel. The join is done with a splicing kit to ensure water tightness.

The kit consists of a long thin plastic case where the electrical cables are joined. Once they are connected, the case is filled with resin giving it mechanical strength and making it completely water tight.

(41)

www.arnalich.com Helping improve humanitarian impact through training and consultancy. You´ll normally order the pump with the specified cable already joined to it. Either way, to resolve silly mistakes or damage to the cable, it´s a good idea to have a spare at hand. For small defects, you can repair with standard fast setting epoxy resin (e.g. Araldite 5 min.).

5. 2 CABLE SELECTION

When electrical current travels through a cable, it´s loses voltage. The longer the distance and the thinner the cable, the greater the voltage drop. Selecting a cable is about finding the thinnest cable which maintains the voltage within the required values. Although you will usually ask the provider to size the cable, it´s not a bad idea to check. You can do so using this table:

Source: Davies and Shirtliff based on recommendations by Grundfos.

5. 3 LEVEL SENSORS

The pump needs water for cooling. If it´s pumping dry, it´ll burn out in a matter of minutes. To avoid this, the pump has integrated level sensors which turn it off automatically if it runs dry.

POWER OF MOTOR MAX. CURRENT MIN. CABLE SECTION

MAX. DISTANCE (m) FOR CABLE SECTION (mm2) kW CV A mm2 1.5 2.5 4 6 10 16 SI N G L E PH A S E 0.37 0.5 3.5 1.5 180 0.55 0.75 5.0 1.5 121 202 0.75 1.0 6.7 1.5 91 152 243 1.10 1.5 7.2 1.5 63 105 168 252 1.50 2.0 10.6 1.5 49 81 130 195 326 2.25 3.0 15.8 2.5 56 89 134 223 T HRE E P HAS E 1.10 1.5 3.1 1.5 382 636 1.50 2.0 3.9 1.5 303 505 2.25 3.0 5.5 1.5 210 350 3.75 5.0 8.7 1.5 131 218 349 5.63 7.5 13.0 2.5 155 248 372 7.50 10.0 17.2 2.5 115 184 276 460 11.30 15.0 24.0 4.0 126 190 316 505 15.00 20.0 32.0 4.0 95 142 237 380 18.80 25.0 40.0 6.0 114 190 304 22.00 30.0 46.0 10.0 164 262

(42)

© Santiago Arnalich Arnalich. Water and habitat www.arnalich.com

5. 4 CONTROL PANEL

The control panel has the ON and OFF button and the protection. There are models that offer greater or lesser levels of sophistication. Your pump supplier can advise you on which panel you should buy.

It´s extremely important that the electrical installation protects people. Protection is provided with a residual current circuit breaker or differential, which opens the circuit when it detects a current leak (which is what happens when someone is electrocuted).

In development contexts it´s common to find control panels without circuit breakers. They are popular because they are cheaper. Avoid them with care, unless the generator or installation already has one installed. Make sure you ask the installers, and look for a switch similar to the trip switches found in houses. They normally have a button with a ´T´ for test.

Fig. 5.4. Control panel with no protection: Differential circuit breaker and ground (green and yellow cable) are missing!

(43)

www.arnalich.com Helping improve humanitarian impact through training and consultancy.

5. 5 GROUND CONNECTION

All electrical installations should be grounded to protect people. A ground connection is a very simple and cheap method of protection against

electrocution. It consists of providing a path of very low resistance such that if there is a leak, the current can travel more easily to ground than through someone. It consists of a metal spike driven into the ground with a salt solution added, connected to the electrical installation via a cable. Ground cables tend to be yellow and green. Connect the ground before doing any operating tests!

GNU Free Documentation license.

5. 6 CHECKING THE DIRECTION OF ROTATION!

Pay attention to this, as it´s a frequent problem which is easy to resolve, but which nonetheless gets people stuck and leads to some strange conclusions (“the borehole has collapsed”, fights over responsibilities, etc.).

If you switch around the two phases of three-phase pumps, the motor changes its direction of rotation. Pumps whose motor spins in the wrong direction continue pumping water, but at much lower pressure and flows, due to the way in which the rotor blades are optimised for operation in one particular direction:

Fig 5.5 Simplified representation of the direction of rotation with respect to blade shape.

(44)

© Santiago Arnalich Arnalich. Water and habitat www.arnalich.com A pump which is pumping in the wrong direction is highly inefficient. Although it will not meet the design requirements it can easily go un-noticed if the installation conditions are not sufficiently demanding. For this reason, it´s fundamental that you check the direction of rotation of any pump you are going to install using a simple method which takes no more than 5 minutes:

1. Connect the pump in a specific way.

2. Turn it on and note the flow and output pressure.

3. Switch the phase cables around and observe what happens.

The connection with higher flow and pressure is the right one. Don´t worry, it´ll be clear which is which.

Fig 5.5b. Correct rotation. “Corner Point”, refugee camp Lugufu I, Tanzania.

When a pump is turned on, it must fill the rising main pipe completely before it begins coming out at the mouth of the borehole. It is normal for the water to take several seconds or minutes to begin coming out.

(45)
(46)

6. Energy

6. 1 GENERATORS

Unless you´re working in urban areas, it´s unlikely you´ll have a nearby electrical supply to connect to. In these cases, power will probably come from a diesel

generator. A generator´s power output is stated in kilowatts (kW), kilovolt amps (kVA) or sometimes in horsepower (HP):

1 kW ≈ 1.25 KVA ≈ 1.36 HP

For three phase generators, the voltage on each phase is indicated after the forward slash: 380/220V, or 415/240V.

How much power do I need?

To work out the power required from the generator, follow these steps:

1. Find out the power of the pump. You´ll find it on the nameplate or in the user manual.

2. Check the surge power factor. Electric motors draw a very large current for a short time when they start up. The pump manufacturer will tell you what it is. If you´re lacking data use a factor of 3. Appendix D shows the minimum values recommended by Grundfos Spain.

3. Derate the generator power. With heat and altitude the generator looses power. If you don´t have manufacturer data, you need to increase the capacity by 0.4% for every degree centigrade above 25º, and 1.4% for every 100m above an altitude of 100m.

(47)

www.arnalich.com Helping improve humanitarian impact through training and consultancy.

Fig 6.1 Installation of a borehole generator in Awr Culus, Somalia.

Calculation example:

Calculate the required generator size to power a 10kW pump, situated at an elevation of 400m in an area where the maximum annual temperature is 34ºC.

STEP 1. The pump consumes 10 kW.

STEP 2. The surge power is: 10 kW * 3 = 30 kW

STEP 3. Derating for altitude: (400m – 100m) * 1.4/100m = 4.2 % For temperature: (34ºC – 25ºC) * 0.4 = 3.6 %

4.2% of 30 kW is: 0.042 * 30 kW = 1.26 kW 3.6% of 30 kW is: 0.036 * 30 kW = 1.08 kW

The required generator power is: 30 kW + 1.26 kW + 1.08 kW = 32.34 kW.

Because there are only specific sizes commercially available, choose the nearest size up.

(48)

© Santiago Arnalich Arnalich. Water and habitat www.arnalich.com

6. 2 CONNECTING TO AN EXISTING ELECTRICAL GRID

Where there´s a grid available with a more or less stable supply, a generator´s not needed. The connection process should be done by qualified personnel, and usually requires authorization from the relevant energy authorities. Depending on the local context, this can add considerable cost to the project.

Fig. 6.2 Electrification of a borehole, Afshar 2, Kabul, Afghanistan. Transformer and utility pole.

(49)

www.arnalich.com Helping improve humanitarian impact through training and consultancy.

6.3 MONO PUMPS

In the generator, the mechanical energy of the diesel engine is transformed into electricity. If the pump has an efficiency of 60% and the alternator in the generator has 60%, the combined output will be:

0.6 x 0.6 *100 = 36%.

Note that the real combined output is much less. If the diesel engine powers the pump directly via belts, these kind of power losses are avoided:

Fig. 6.3. Borehole equipped with a Mono pump.

Mono pumps are those that work through displacement, between two parts that engage with each other, leaving a small gap between the two. The gaps are displaced upwards like a never ending screw, similar to the Archimedes screw:

(50)

7. Ordering materials

The arrival of materials with nothing missing and on time is essential to avoid delays. This chapter shows you how to order the material you need.

7. 1 RULES FOR THE PURCHASING PROCESS

You can´t usually just go off and buy the materials when it suits you. To avoid corruption, the diversion of funds, and to encourage free competition between suppliers, the purchasing process calls for a regulated procedure once you move beyond certain quantities.

These rules basically define who has to sign the authorization of purchases and how many supplier quotes are needed.

For practical purposes, establish:

1. Who has to authorize your order and what are the rules within your organization.

2. Above and beyond which quantity these rules come into play.

3. If there are limitations to what you can buy, decided by the donor. For example, if all materials which cost more than a certain amount need to be bought in the EU (Arrrgh!).

(51)

www.arnalich.com Helping improve humanitarian impact through training and consultancy.

7. 2 THE IMPORTANCE OF COMMUNICATION

There will normally be a person or a logistics department that takes care of placing orders. This person or department won´t necessarily be a specialist in water supply. Since human nature is an old friend of ours, unintelligible orders tend to “eat up” desk space indefinitely and when they are finally processed, you´re left with a never ending list of errors and misunderstandings. For your order to arrive on site quickly and without nasty surprises:

1. Define all the material precisely leaving no room for doubt. You´ll soon see how.

2. Add diagrams and images to the order. The person in charge of the purchase can then show these to the supplier. This makes their job much easier and avoids misunderstandings.

3. For less common accessories, include second and third options in case your first choice isn´t available.

4. Divide your order into areas, for example, all materials related to the pump together in one section. That way you´ll avoid one accessory holding up the whole order and will make the logistics easier.

(52)

© Santiago Arnalich Arnalich. Water and habitat www.arnalich.com

7. 3 ORDERING WITH PRECISION

The point here is to define each accessory with its particular characteristics leaving no room for doubt.

The pump

You need to stay on top of this personally, even if there´s a purchasing department, to avoid being left with a pump which may be the cheapest but isn´t what´s required. It’s best to find out which 3 pumps are closest to what you need, get a quote for each, and if they are in the same price range, buy the one that meets the requirements, based on strictly technical criteria. Avoid, at all costs, low quality pumps (generally from China or India).

The operating frequency will depend on the country you´re in. In most places, as in Europe, the frequency is 50 Hz. In parts of the Americas it´s 60 Hz.

PUMP: Specify the manufacturer, model, frequency and outlet connection:

1 unit Submersible pump Grundfos SP 8A-15, 50 Hz, threaded outlet.

Splicing kit

The number of phases and the voltage is determined by the pump. The kits are made to fall into voltage ranges (e.g. Low voltage 0-600V), and they are ordered from the pump supplier.

SPLICING KIT: Voltage and number of phases:

1 unit Submersible splicing kit, 3 phase, 415V.

Submersible cable

Order 20 or 30 meters more than you need to allow for modifications or mistakes.

SUBMERSIBLE CABLE: Length, section, number of phases and connection to pump:

245 m Submersible cable 6mm2, 3-phase, connected to the pump.

Control panel

This is usually ordered from the pump supplier and you don´t need to provide all that much detail, just make sure it comes with a differential circuit breaker (section 5.4). It must have the same power capacity as that of the pump.

CONTROL PANEL: Power, voltage, number of phases, frequency and differential breaker:

(53)

www.arnalich.com Helping improve humanitarian impact through training and consultancy.

1 unit Control panel 7.5 kW, 3-phase, 415V with differential circuit breaker.

The generator

Any medium sized generator will be diesel. To make sure spares are available, don´t try and be too clever and order a model that comes from the other side of the world. Locally available generators are the best. They may come with a covering to protect them in outdoor conditions. Specify the operating conditions, especially temperature, so that the lubricants and coolants are suited to the local environment. Depending on the configuration of the pump house, you may need to order ducts for the exhaust gases. Remember that 1 kVa is approximately 0.8kW.

GENERATOR: Fuel, power, voltage, number of phases, protection and temperature.

1 unit Diesel Generator, 30 kVa, 415/240V, without housing, working at 20º-40ºC.

Ground connection

They come in the form of kits. Let the supplier work out the length and section of the spike. If you´re connecting to an existing grid, the ground connection will come as part of the contracted design.

1 unit Ground connection kit for the generator

Material for connection to an existing grid

In many cases it´s convenient to include this material in the implementation contract. That way the company carrying out the contract is responsible for the purchase of the materials. Either way, include a materials list with approximate prices in the design contract.

Pipes and accessories

Rising pipe is ordered by the number of pipes of a given length, either 3 or 6m. It´s best to use 6m lengths, which will half the installation work required and reduce the risk of leaks. You’ll need a piece 1m long to attach to the pump and probably another piece to arrive to the installation depth if it is not multiple of 6m (or 3m).

If you need plastic pipe to avoid corrosion, use HDPE. It´s easiest to order a roll of pipe to meet the installation depth, together with the joining accessories to fix to a threaded end, already welded on. Rolls of HDPE are only available in diameters of 4” or less. If using galvanized iron, remember to order the connecting sockets!

RISING MAIN: Material, diameter, pressure, presentation and connection:

(54)

© Santiago Arnalich Arnalich. Water and habitat www.arnalich.com

82m HDPE pipe, 3”, 10 bar, single roll, with 2 welded ends, threaded

Fig. 7.3. Connection of HDPE pipe, in a roll, to a submersible pump.

ACCESSORIES: Type (material), diameter, pressure, and connection:

1 unit Elbow, galvanised iron, 4”, 25 bar, threaded union. 2 units Gate valve 4”, 10 bar, threaded union.

60 units Sockets, galvanised iron, 4”, 25 bar.

Accessories can be joined with threaded joints, generally up to 4”, or with bolted flanges, for 4” and greater:

(55)

www.arnalich.com Helping improve humanitarian impact through training and consultancy. In some cases, notably water meters and for anything over 4” in diameter,

accessories don´t have a threaded union, and a transition between threaded pipe and flange has to be made. The simplest is to do it with a short pipe, threaded on one end and with a flange on the other.

When pipes are threaded, systems quickly become impossible to assemble and disassemble. For a T, for example, the whole installation would have to be rotated to assemble the pipes. Moreover, a breakage at one point will require disconnecting the entire installation until that point is reached. Unions are used to allow the pipes to be taken apart, shown with arrows in the photograph:

Steel cable

Pumps are fixed with a braided steel cable to avoid fall during installation and removal, or in case of corrosion or a faulty pipe union. For plastic pipes, the cable prevents the pipe extending fully that would result in the pump being installed at an incorrect level. When the water is corrosive, the cable is protected by a PVC coating.

The cable is attached to the body of the pump, and is fixed with 3 cable clamps. The same is done at the mouth of the borehole. When there is no cable, use a rope tied with a bowline knot (Appendix F) fixed below the lid (synthetic ropes disintegrate in the sun).

CABLE: Diameter, coating CLAMPS: Diameter.

100m Steel cable 4mm in single roll with PVC coating 6 units Cable clamps 4mm.

(56)

© Santiago Arnalich Arnalich. Water and habitat www.arnalich.com

Submersible cable clamps

To prevent the cables getting snagged they are fixed to the rising main every 3 meters. Although most suppliers have rubber clamps, this is commonly done with strips of rubber cut from an inner tube.

Borehole cover

This closes off the borehole once the pipes have been installed. It can be screwed onto the rising main or made out of two plates that join together, leaving a circular gap between them. The second system requires an omega clamp to attach to the pipe, the same one that´s used while the pump is being lowered. In both cases, there needs to be enough space for the submersible cable and for a piezometric level meter to measure the water levels (a hole 3cm in diameter is sufficient).

The cover in two parts is usually made to order from a blacksmith providing the required dimensions.

BOREHOLE COVER: Diameter of rising main, system and diameter to cover.

1 unit Borehole cover 4” screwed on to rising main, with ring for steel cable. Diameter greater than 12”

7. 4 CRITICAL MATERIAL

These are the most problematic materials and those that require the most time.

Subcontracts

Some organizations consider implementation contracts as a purchase. In this case, you´ll have to “place an order” for them. Either way, the electrical connection and pump house construction contracts will be sufficiently large to call for 3 quotes from 3 different companies. Getting the quotes back takes time, so if you need these kind of contracts, get on the case sooner rather than later.

(57)

www.arnalich.com Helping improve humanitarian impact through training and consultancy. You can install part of the equipment without the pump house, or build the house before the installation, but both need to be finished for operation to begin.

Expensive material

There are various reasons for ordering the pump and generator early on:

1. They tend to require internal authorisations and quotes from 3 suppliers.

2. The pump you need may not be in stock. Manufactures tend only to stock the most common pumps and the rest are made to order.

3. In some cases, they need to be ordered from another country. The further away that is, the more likely it is that it´ll arrive late and damaged.

7. 5 DIVIDING UP ORDERS

In my experience, it´s not a good idea to place all the materials in one order.

Problems, delays and incidents for one element affect all the rest, and getting quotes becomes more complicated, as not all suppliers offer the same services. A division of orders which can avoid problems like this is:

1. Order the generator, ground connections and spares in one order.

2. Pump, control panel, submersible cable, borehole cover and splicing kit in another.

3. Pipe accessories (the pipe itself comes in the next order). For HDPE, include the pipe here with all the unions already made.

4. Rising main with connection sockets (for GI pipes).

The rest of the materials, non-submersible electrical cable, steel pipes etc. can be bought beforehand, locally.

7. 6 QUALITY

The purchasing departments tend not to be very familiar with the materials and usually their only criteria for comparison between quotes is their cost. Quality is fundamental for these installations. Actively offer your support and advice.

(58)

© Santiago Arnalich Arnalich. Water and habitat www.arnalich.com Avoid low quality pumps and accessories, which have “Made in England” written on them but which look suspect and products resulting from recycling acrobatics. Note, for example, the irregular outline, lumps, bubbles and burrs on this gate valve:

(59)
(60)

8. The Installation

“Often a few hours of trial and error can save you a couple of minutes reading the manual.”

(Anonymous)

Each pump has it´s peculiarities. You don´t want to spend a day under the sun, with the whole team working hard, only to discover that the pump which is 150 m below your feet has a small plastic safety mechanism which stops it turning accidentally during transport. Read the manual even before you think of installing it!

8. 1 LOWERING THE PUMP

The main part of the installation involves the placement of the pump. Lowering and positioning the pump requires the greatest level of coordination and effort. It can take anything from a few hours to an entire day, depending on the depth of the borehole and the number of connections.

The process consists of introducing the pump vertically into the borehole while connecting the piping. As each section of pipe is connected, the pump is lowered 3 or 6m. This continues until the installation depth is reached. The detailed process is described below:

1. If you´re using galvanised steel pipe, prepare some of the pipe sections by fixing the threaded sockets on one end, and wrapping Teflon tape or fibers on the other. The coupling will stop the pipe from falling if the clamp slips.

(61)

www.arnalich.com Helping improve humanitarian impact through training and consultancy. 2. Drive a section of steel pipe 80cm into the ground, inclined at an angle of 30º

in the opposite direction of the borehole. It´ll act as a brake post to prevent the pump accidentally falling down the borehole. The steel cable is looped around it three times, which will stop it slipping in case of a fall. One person is in charge of letting the cable out as the pump is lowered.

3. Remove the pump from its box and lay it on a smooth horizontal surface, so that it´s supported over its entire length. It´s easy for the pump shaft to become deformed if not.

4. Join the submersible cable with the splicing kit if the manufacturer hasn´t already done so. Never handle the pump by pulling on this cable!

5. Pass the steel cable through the holes of the pump casing and fix 3 cable clamps, 5cm apart:

(62)

© Santiago Arnalich Arnalich. Water and habitat www.arnalich.com 6. Join the first pipe section to the pump. Take special care not to damage the

pump and don´t use any kind of tool to hold or turn it. For the join to be watertight, use Teflon tape or natural fibres. By the end of this step you´ll have the pump, with the electrical cable and the first pipe section connected. The first pipe section is 1 meter long, to make entering the borehole easier. If the pipe is galvanised steel, screw a coupling on the end to act as a buffer.

7. Place the first omega clamp over the short pipe section, joined to the pump, with the second over the next pipe section together with the coupling. Make sure you tighten the screws properly so it doesn´t slip down the pipe.

8. Fix the cable protector clip. This is a homemade part, consisting of a small length of steel pipe 1” in diameter, 20cm long, with a clip welded on the side. The submersible cable is passed through the middle and the clip is fixed to the inside of the borehole entrance.

Its purpose is to protect the cable mechanically. It´s very common during an

installation for the column to pinch the cable against the mouth of the borehole and damage it.

(63)

www.arnalich.com Helping improve humanitarian impact through training and consultancy. 9. Raise the pump and pipe with the crane and align it with the mouth of the

borehole. The crane tends to be manual, chain operated, with a tripod. If you can afford a loader crane, it´ll speed things up.

10. Lower the pump until the clamp rests on the mouth of the borehole. Fix the submersible cable to the rising main with rubber clamp, but this time, leave the steel cable out.

(64)

© Santiago Arnalich Arnalich. Water and habitat www.arnalich.com 11. Release the crane, and let the column rest entirely on the clamp. Fix the pipe

section with the second clamp on it to the crane, and place it over the coupling at the end of the column. Thread the pipe into the column. If you have problems, use vegetable oil (i.e. sunflower or palm oil) as a lubricant.

Observe that while two people work joining the pipe, another in the foreground already has the next one ready, with a third person (sitting on the roll of rope to the right) in charge of the braking post:

12. Half way up, and at the end of each pipe section, the cables are fixed to the rising main with a rubber clamp.

13. This continues until the installation depth is reached. Once there, the borehole lid is screwed in, and the non-threaded lid is fixed in place. The steel cable is also passed through the ring on the lid and secured with clamps. Remember there are 3 things referred to as clamps: the omega shaped ones which secure the pipe, the rubber ones which secure the cable to the pipe, and the ones that clamp the steel cable to itself.

14. Remove the protection clip and pass the submersible cable through the hole in the lid, made for that purpose.

Figure

Updating...

Related subjects :