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The Centrifugal Pump

Manufacturing Engineering Processes
Engineering and Technical Mathematics

The Centrifugal Pump
Christian Brix Jacobsen Department Head,
Structural and Fluid Mechanics, R&T
126 pages

Open: The Centrifugal Pump
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’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. 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 inspiration in their studies. Our intention has been to write an introductory book that gives an overview of the hydraulic components in the pump and at the same time enables technicians to see how changes in construction and operation influence the pump performance.

TOC

Chapter 1.
Introduction to Centrifugal Pumps ...............11
Principle of centrifugal pumps.......................................12
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.................23
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 pump...............................................................27
Summary.............................................................................................27

Chapter 2.
Performance curves ............................................29
Standard curves ...................................................................... 30
Pressure ..........................................................................................32
Absolute and relative pressure ......................................33
Head ............................................................................................ 34
Differential pressure across the pump ....................35
Total pressure difference .................................35
Static pressure difference.................................35
Dynamic pressure difference..........................35
Geodetic pressure difference ........................ 36
Energy equation for an ideal flow................................37
Power .............................................................................................. 38
Speed.............................................................................. 38
Hydraulic power ...................................................................... 38
Efficiency....................................................................................... 39
NPSH, Net Positive Suction Head................................ 40
Axial thrust.................................................................................. 44
Radial thrust............................................................................... 44
Summary .......................................................................................45

Chapter 3.
Pumps operating in systems ........................... 47
Single pump in a system.................................................... 49
Pumps operated in parallel.............................................. 50
Pumps operated in series................................................... 51
Regulation of pumps............................................................. 51
Throttle regulation ................................................52
Regulation with bypass valve ........................52
Start/stop regulation...........................................53
Regulation of speed ..............................................53
Annual energy consumption ......................................... 56
Energy efficiency index (EEI).............................................57
Summary ...................................................................................... 58

Chapter 4.
Pump theory .........................................................59
Velocity triangles....................................................................60
Inlet ................................................................................. 62
Outlet............................................................................. 63
Euler’s pump equation........................................................ 64
Blade shape and pump curve.........................................66
Usage of Euler’s pump equation.................................... 67
Affinity rules............................................................................... 68
Derivation of affinity rules .............................. 70
Pre-rotation .................................................................................72
Slip......................................................................................................73
The pump’s specific speed.................................................74
Summary ....................................................................................... 75

Chapter 5.
Pump losses ............................................................ 77
Loss types ......................................................................................78
Mechanical losses................................................................... 80
Bearing loss and shaft seal loss................... 80
Hydraulic losses....................................................................... 80
Flow friction................................................................81
Mixing loss at cross-section expansion ............................ 86
Mixing loss at cross-section reduction ......................................87
Recirculation loss................................................... 89
Incidence loss ...........................................................90
Disc friction................................................................ 91
Leakage......................................................................... 92
Loss distribution as function of specific speed ............................................................................ 95
Summary ...................................................................................... 95

Chapter 6.
Pumps tests ................................................ 97
Test types..................................................................................... 98
Measuring pump performance.....................................99
Flow...............................................................................100
Pressure ....................................................... 100
Temperature ........................................................... 101
Calculation of head ............................................ 102
General calculation of head ....................103
Power consumption........................................... 104
Rotational speed.................................................. 104
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 density....................... 108
Reference plane.................................................... 108
Barometric pressure ..........................................109
Calculation of NPSHA and determination of NPSH3%...................................................................109
Measurement of force ......................................................109
Measuring system............................................... 110
Execution of force measurement.............. 111
Uncertainty in measurement of performance.. 111
Standard demands for uncertainties...... 111
Overall uncertainty..............................................112
Test bed uncertainty ..........................................112