GRUNDFOS RESEARCH AND TECHNOLOGY

1 The Centrifugal PumpGRUNDFOSRESEARCH AND TECHNOLOGYThe Centrifugal Pump5 All rights , electronic, photographic or other reproduction or copying from this book or parts of it are according to the present Danish copyright law not allowed without written permission from or agreement with GRUNDFOS Management A/S. GRUNDFOS Management A/S cannot be held responsible for the correctness of the information given in the book. Usage of information is at your own responsibility. 6 PrefaceIn the Department of Structural and Fluid Mechanics we are happy to present the first English edition of the book: The Centrifugal Pump . We have written the book because we want to share our knowledge of pump hy-draulics, pump design and the basic pump terms which we use in our daily work. The Centrifugal Pump is primarily meant as an inter-nal book and is aimed at technicians who work with development and construction of pump components.

2 Furthermore, the book aims at our future colleagues, students at universities and engineering colleges, who can use the book as a reference and source of inspira-tion in their studies. Our intention has been to write an introductory book that gives an overview of the hy-draulic components in the pump and at the same time enables technicians to see how changes in construc-tion and operation influence the pump performance. In chapter 1, we introduce the principle of the centrifu-gal pump as well as its hydraulic components, and we list the different types of pumps produced by GRUNDFOS . Chapter 2 describes how to read and understand the pump performance based on the curves for head, pow-er, efficiency and NPSH. In chapter 3 you can read about how to adjust the pump s performance when it is in operation in a system. The theoretical basis for energy conversion in a centrifu-gal pump is introduced in chapter 4, and we go through how affinity rules are used for scaling the performance of pump impellers.

3 In chapter 5, we describe the differ-ent types of losses which occur in the pump, and how the losses affect flow, head and power consumption. In the book s last chapter, chapter 6, we go trough the test types which GRUNDFOS continuously carries out on both assembled pumps and pump components to ensure that the pump has the desired performance. The entire department has been involved in the devel-opment of the book. Through a longer period of time we have discussed the idea, the contents and the structure and collected source material. The framework of the Danish book was made after some intensive working days at Himmelbjerget . The result of the department s engagement and effort through several years is the book which you are holding. We hope that you will find The Centrifugal Pump use-ful, and that you will use it as a book of reference in you daily work. Enjoy!Christian Brix Jacobsen Department Head, Structural and Fluid Mechanics, R&T7 ContentsChapter 1.

4 Introduction to Centrifugal Pumps .. Principle of centrifugal pumps .. The pump s hydraulic components ..13 Inlet flange and inlet ..14 impeller ..15 Coupling and drive ..17 impeller seal ..18 Cavities and axial bearing ..19 Volute casing, diffuser and outlet flange ..21 Return channel and outer sleeve .. Pump types and systems ..24 The UP pump ..25 The TP pump ..25 The NB pump ..25 The MQ pump ..25 The SP pump ..26 The CR pump ..26 The MTA pump ..26 The SE The SEG pump .. Summary ..27 Chapter 2. Performance curves .. Standard curves .. Pressure .. Absolute and relative pressure .. Head .. Differential pressure across the pump ..35 Total pressure difference ..35 Static pressure difference ..35 Dynamic pressure difference ..35 Geodetic pressure difference .. Energy equation for an ideal flow .. Power ..38 Speed .. Hydraulic power .. Efficiency.

5 NPSH, Net Positive Suction Head .. Axial Radial thrust .. Summary ..45 Chapter 3. Pumps operating in systems .. Single pump in a Pumps operated in parallel .. Pumps operated in series .. Regulation of pumps ..51 Throttle regulation ..52 Regulation with bypass valve ..52 Start/stop regulation ..53 Regulation of speed .. Annual energy consumption .. Energy efficiency index (EEI).. Summary ..58 Chapter 4. Pump theory .. Velocity triangles ..60 Inlet ..62 Outlet .. Euler s pump equation .. Blade shape and pump curve .. Usage of Euler s pump equation .. Affinity rules ..68 Derivation of affinity rules .. Pre-rotation .. Slip .. The pump s specific speed .. Summary ..75 Chapter 5. Pump losses .. Loss types .. Mechanical losses ..80 Bearing loss and shaft seal loss .. Hydraulic losses ..80 Flow Mixing loss at cross-section expansion ..86 Mixing loss at cross-section reduction.

6 87 Recirculation loss ..89 Incidence loss ..90 Disc friction ..91 Leakage .. Loss distribution as function of specific speed .. Summary ..95 Chapter 6. Pumps tests .. Test types .. Measuring pump performance ..99 Flow ..100 Pressure ..100 Temperature ..101 Calculation of head ..102 General calculation of head ..103 Power consumption ..104 Rotational speed .. Measurement of the pump s NPSH ..105 NPSH3% test by lowering the inlet pressure ..106 NPSH3% test by increasing the flow ..107 Test beds ..107 Water quality ..108 Vapour pressure and Reference plane ..108 Barometric pressure ..109 Calculation of NPSHA and determination of NPSH3% .. Measurement of force ..109 Measuring system ..110 Execution of force measurement .. Uncertainty in measurement of performance .. 111 Standard demands for uncertainties ..111 Overall uncertainty ..112 Test bed uncertainty.

7 Summary ..112 Appendix ..113A. Units ..114B. Control of test results ..117 Bibliography ..124 Substance values for water ..131 List of Symbols ..132 910 Chapter 1 Introduction to centrifugal Principle of the centrifugal Hydraulic components Pump types and SummaryOutletImpellerInlet1212 OutletImpellerInletDirection of rotation1. Introduction to Centrifugal Pumps1. Introduction to Centrifugal PumpsIn this chapter, we introduce the components in the centrifugal pump and a range of the pump types produced by GRUNDFOS . This chapter provides the reader with a basic understanding of the principles of the centrifugal pump and pump centrifugal pump is the most used pump type in the world. The principle is simple, well-described and thoroughly tested, and the pump is robust, ef-fective and relatively inexpensive to produce. There is a wide range of vari-ations based on the principle of the centrifugal pump and consisting of the same basic hydraulic parts.

8 The majority of pumps produced by GRUNDFOS are centrifugal pumps. Principle of the centrifugal pumpAn increase in the fluid pressure from the pump inlet to its outlet is cre-ated when the pump is in operation. This pressure difference drives the fluid through the system or plant. The centrifugal pump creates an increase in pressure by transferring me-chanical energy from the motor to the fluid through the rotating impeller . The fluid flows from the inlet to the impeller centre and out along its blades. The centrifugal force hereby increases the fluid velocity and consequently also the kinetic energy is transformed to pressure. Figure shows an ex-ample of the fluid path through the centrifugal pump. Figure : Fluid path through the centrifugal Hydraulic componentsThe principles of the hydraulic components are common for most centrifu-gal pumps. The hydraulic components are the parts in contact with the fluid.

9 Figure shows the hydraulic components in a single-stage inline pump. The subsequent sections describe the components from the inlet flange to the outlet flange. Figure : Hydraulic flangeCavity above impellerCavity below impellerImpeller sealInlet flangeVoluteInletShaftCouplingPump housingImpellerShaft sealImpeller Inlet14141. Introduction to Centrifugal Inlet flange and inletThe pump is connected to the piping system through its inlet and outlet flanges. The design of the flanges depends on the pump application. Some pump types have no inlet flange because the inlet is not mounted on a pipe but sub-merged directly in the inlet guides the fluid to the impeller eye. The design of the inlet depends on the pump type. The four most com-mon types of inlets are inline, endsuction, doublesuction and inlet for submersible pumps, see figure pumps are constructed to be mounted on a straight pipe hence the name inline.

10 The inlet section leads the fluid into the impeller pumps have a very short and straight inlet sec-tion because the impeller eye is placed in continuation of the inlet flange. The impeller in doublesuction pumps has two impeller eyes. The inlet splits in two and leads the fluid from the inlet flange to both impeller eyes. This design minimises the axial force, see section In submersible pumps, the motor is often placed below the hydraulic parts with the inlet placed in the mid section of the pump, see figure The design prevents hydraulic los-ses related to leading the fluid along the motor. In addition, the motor is cooled due to submersion in the fluid. Figure : Inlet for inline, endsuction, doublesuction and submersible pumpEndsuction pumpDoublesuction pumpSubmersible pumpImpeller InletImpeller InletImpeller Inlet1515 Figure : Velocity distribution in plateHubTrailing edge Shroud plateLeading edgeImpeller channel (blue area) impeller bladeThe impeller s direction of rotation Tangential direction Radial direction Axial directionThe impeller s direction of rotationFigure : The impeller components, definitions of directions and flow relatively to the design of the inlet aims at creating a uniform velocity profile into the impeller since this leads to the best performance.