Working Guide to Pump and Pumping Stations

Calculations and Simulations

E. Shashi Menon

• Publisher: Gulf Professional Publishing
• Year: 2009
• ISBN:
  9781856178297
• Topic: Technology & Engineering
• Subtopic: Mechanical Engineering
• Index: Technology & Engineering

Working Guide to Pumps and Pumping Stations: Calculations and Simulations discusses the application of pumps and pumping stations used in pipelines that transport liquids. It provides an introduction to the basic theory of pumps and how pumps are applied to practical situations using examples of simulations, without extensive mathematical analysis. The book begins with basic concepts such as the types of pumps used in the industry; the properties of liquids; the performance curve; and the Bernoullis equation. It then looks at the factors that affect pump performance and the various methods of calculating pressure loss in piping systems. This is followed by discussions of pump system head curves; applications and economics of centrifugal pumps and pipeline systems; and pump simulation using the software PUMPCALC. In most cases, the theory is explained and followed by solved example problems in both U.S. Customary System (English) and SI (metric) units. Additional practice problems are provided in each chapter as further exercise. This book was designed to be a working guide for engineers and technicians dealing with centrifugal pumps in the water, petroleum, oil, chemical, and process industries.

• Calculations for their selection, sizing and power output
• Case studies based on the author's 35 years of field experience
• Covers all types of pumps
• Simplified models and simulations

Chapter 1 Introduction

The function of a pump is to increase the pressure of a liquid for the purpose of transporting the liquid from one point to another point through a piping system or for use in a process environment. In most cases, the pressure is created by the conversion of the kinetic energy of the liquid into pressure energy. Pressure is measured in lb/in² (psi) in the U.S. Customary System (USCS) of units and in kPa or bar in the Systeme International (SI) system of units. Other units for pressure will be discussed in the subsequent sections of this book. Considering the transportation of a liquid in a pipeline, the pressure generated by a pump at the origin A of the pipeline must be sufficient to overcome the frictional resistance between the liquid and the interior of the pipe along the entire length of the pipe to the terminus B. In addition, the pressure must also be sufficient to overcome any elevation difference between A and B. Finally, there must be residual pressure in the liquid as it reaches terminus B if it is to perform some useful function at the end.

If the elevation of B is lower than that of A, there is an elevation advantage where the pump is located that will result in a reduction in the pressure that must be generated by the pump. Conversely, if the elevation of B is higher than that of A, the pump has to work harder to produce the additional pressure to overcome the elevation difference.

Types of Pumps

Several different types of pumps are used in the liquid pumping industry. The most common today is the centrifugal pump, which will be covered in detail in this book. Other types of pumps include reciprocating and rotary pumps. These are called positive displacement (PD) pumps because in each pumping cycle or rotation, the pump delivers a fixed volume of liquid that depends on the geometry of the pump and the rotational or reciprocating speed. In PD pumps, the volume of liquid pumped is independent of the pressure generated. These pumps are able to generate very high pressure compared to centrifugal pumps. Therefore, safety devices such as a rupture disk or a pressure relief valve (PRV) must be installed on the discharge of the PD pumps to protect the piping and equipment subject to the pump pressure.

Centrifugal pumps are capable of providing a wide range of flow rate over a certain pressure range. Hence, the pressure generated by a centrifugal pump depends on the flow rate of the pump. Due to the variation in flow versus pressure, centrifugal pumps are more flexible and more commonly used in process and pipeline applications. They are used in pumping both light and moderately heavy (viscous) liquids. Many applications involving very heavy, viscous liquids, however, may require the use of PD pumps, such as rotary screw or gear pumps, due to their higher efficiency.

Rotary pumps, such as gear pumps and screw pumps, shown in Figure 1.1, are generally used in applications where high-viscosity liquids are pumped. As mentioned before, these PD pumps are able to develop high pressures at fixed flow rates that depend on their design, geometry, and rotational speed.

Figure 1.1 Gear pump and screw pump.

The operating and maintenance costs of centrifugal pumps are lower compared to PD pumps. In general, PD pumps have better efficiency compared to centrifugal pumps. The recent trend in the industry has been to more often use centrifugal pumps, except for some special high-viscosity and metering applications, where PD pumps are used instead. Since the water pipeline, chemical, petroleum, and oil industries use mostly centrifugal pumps for their pumping systems, our analysis throughout this book will be geared toward centrifugal pumps.

Centrifugal pumps may be classified into the following three main categories:

• Radial flow pumps
• Axial flow pumps
• Mixed flow pumps

Radial flow pumps develop pressure by moving the pumped liquid radially with respect to the pump shaft. They are used for low flow and high head applications. Axial flow or propeller pumps develop pressure due to the axial movement of the pumped liquid and are used for high flow and low head applications. The mixed flow pumps are a combination of the radial and axial types, and they fall between these two types. The specific speed of a pump, discussed in Chapter 2 is used to classify the type of centrifugal pumps. Radial flow pumps have low specific speeds (less than 2000), while axial flow pumps have high specific speeds (greater than 8000). Mixed flow pumps fall in between.

Figure 1.2 shows a typical centrifugal pump, which can be classified as a volute-type or a diffuser-type pump. The single-volute centrifugal pump in Figure 1.3 converts the velocity head due to the rotational speed of the impeller into static pressure as the liquid is hurled off the rotating impeller into the discharge pipe. Double volute pumps work similar to the single volute ...

Table of contents

• Cover
• Title Page
• Copyright
• Dedication
• Preface
• Author Biography
• Chapter 1: Introduction
• Chapter 2: Pump Performance
• Chapter 3: Liquid Properties versus Pump Performance
• Chapter 4: Pressure Loss through Piping Systems
• Chapter 5: System Head Curves
• Chapter 6: Pump Performance at Different Impeller Sizes and Speeds
• Chapter 7: NPSH and Pump Cavitation
• Chapter 8: Pump Applications and Economics
• Chapter 9: Pump Simulation Using PUMPCALC Software
• Appendices
• References
• Index