Chapter Six: Pumping Systems

From Ministry of Water DCOM Manual

1 Chapter Six: Pumping Systems

1.1 1.1 Introduction

This section describes the water supply pumping systems. Brief presentation of types of pumps are provided. Also, it describes how to design and select pumps for a water supply system. Lastly, it gives key considerations in their installation. It is important to understand the different types of pumps, design procedures, source of pumping power, motor starting, machine protections and economics of electric power systems. However, more details on pump types and their functioning are given in Appendix E.

1.2 1.2 Rationale

The main goal of any pumping plant and pumping system is to lift water from a lower to a higher level.

1.3 1.3 Common Types of Pumps used in water supply

There are two main pump types used in the water supply projects which are different in design and application. Table 6.1 shows the most commonly used pump types. Further details of each type of pumps can be seen in Appendix E of this DCOM manual.

1.3.1 Table 6.1: Most Commonly Used Pump Types

Main Types Sub-types Specific types
Rotordynamic Centrifugal Single-stage
Multi-stage shaft driven
Multi-stage submersible
Peripheral Axial flow
Mixed flow
Turbine
Submersible
Positive displacement Reciprocating Suction (shallow well)
Lift (deep well)
Rotary Helical Rotor

(Source: Modified from Uganda water design manual 2013)

1.4 1.4 Pumping System Setup

When setting up the pumping system, carefully calculate the driver Horse Power (HP) required based on the data on the flow, pressure and efficiency of the pump. Check the pump RPM and drive RPM and select the proper size pulleys to achieve the desired flow. Review the maximum horsepower per belt to assure that the pump receives adequate power to deliver the desired flow. The correct belt length and centre distance must be established to achieve the proper HP. If in doubt, consult your pump and/or drive supplier for their recommendations.

1.5 1.5 Source of Pumping Power

The different types of power sources commonly used for water supply pumps include:

  • Electrical grid power
  • Diesel/gasoline generators and engines
  • Natural gas/biogas generators
  • Solar Energy
  • Wind Energy

The choice of pumping energy depends on several factors namely:

  • Availability of and proximity to grid power,
  • Capital costs of the alternatives,
  • Operational costs of the alternatives.

In Tanzania when deciding on the pumping energy, grid power is considered as the basic source in the sense that when available it becomes the 1st choice. It is only when the grid source is too far from the pumping point that the other sources are considered. The three alternatives to grid power namely diesel/petrol/natural gas/biogas generators or engines have both positives and negatives. In the following subchapters each alternative shall be discussed.

1.6 1.6 Pumping system design pump selection

Pump selection involves selecting the type of pump that fits the application and sizing the pump to be able to deliver the required pressure and flow to the point of delivery. The factors which should be considered in the selection and sizing of a pump include:

  1. Depth to the water level and its seasonal variations;
  2. Pressure ranges needed for adequate water supply;
  3. Heights through which water has to be lifted, both below and above the pump;
  4. Pump location;
  5. Pump durability and efficiency.

The type of pump selected for a particular installation should be determined on the basis of the following fundamental considerations:

  1. Yield of the well or water source;
  2. Daily needs and instantaneous demand of the users;
  3. The “usable water” in the pressure or storage tank;
  4. Size and alignment of the well casing;
  5. Total operating head pressure of the pump at normal delivery rates, including lift and all friction losses;
  6. Difference in elevation between ground level and water level in the well during pumping;
  7. Availability of power;
  8. Ease of maintenance and availability of replacement parts;
  9. First cost and economy of operation;
  10. Reliability of pumping equipment; and
  11. Pump start-up problem and time.

Tables 6.2(a) and (b) shows the operation ranges of different type of pumps according to the head required and the flow rate needed. For water supply pumps the two have to be considered for a good pump. Examples of pump duty calculations is provided in Appendix E.

1.6.1 Table 6.2 (a): Selection of types of pumps for water supply by the head needed

Under 10 m From 10 to 100 m From 100 to 1,000 m From 1,000 to 10,000 m From 10,000 m and over
One-stage centrifugal pumps
Multistage centrifugal pumps
Axial flow pumps (head is up to 20-30 m)
Piston pumps
Screw pumps
Plunger pumps
Vortex pumps

1.6.2 Table 6.2 (b): Selection of types of pumps for water supply by flowrate needed

Under 10 m3/h From 10 to 100 m3/h From 100 to 1,000 m3/h From 1,000 to 10,000 m3/h From 10,000 m3/h and over
One-stage centrifugal pumps
Multistage centrifugal pumps
Axial flow pumps
Piston pumps
Screw pumps
Plunger pumps
Vortex pumps

1.7 1.7 Pump Protection

In order to ensure acceptable technical soundness of plants and pumping systems the following protective measures need to be considered at the design stage and adopted wherever desirable. For the purpose of avoiding unnecessary sophistication and yet establish reliable protection of plants and pumping systems the protective systems enumerated hereunder shall be adopted in the fashion recommended herein:

  1. Protection against dry running
  2. Protection against water hammer
  3. Protection against cavitation’s
  4. Protection against overloads/over current
  5. Protection against cathodic corrosion.

The most important protection is water hammer of which it can be analysed through number of software. Of these, the one recommended for consideration is Surge 2000 produced as part of the KYpipe software package, and details can be found by logging on to their website. A 250 pipe solution costed US$ 3,000 in 2006.

Another alternative, especially if the designer is interested in pursuing a controlled air transient technology (CATT) approach to the use of air-valves is to contact Vent-O-Mat of South Africa by logging on to their website.

1.8 1.8 References

MoW 3rd Edition Design Manual, 2009 Uganda Water Design Manual, 2013