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P L A N T S U P P O RP L A N T S U P P O R T E N G I N E E R I N GT E N G I N E E R I N G
Engineering Training Modules forNuclear Plant Engineers
EPRI TR-109623
Mechanical SeriesModule #4
April 15, 1999
Centrifugal Pumps

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Table of Contents
1.0 SCOPE AND PURPOSE 1
2.0 SUGGESTED PRIOR SKILLS AND KNOWLEDGE 1
3.0 OBJECTIVES 1
4.0 NOMENCLATURE 2
5.0 PRINCIPLES AND PROPERTIES 2
5.1 Pump Types 2
5.2 Impeller Types 5
5.3 Pump Head Terminology 7
5.4 Pump Affinity Laws 12
5.5 Pump Specific Speed 13
5.6 Pump Suction Specific Speed 13
5.7 Pump Bearings 14
5.8 Pump Shaft Seals 15
5.9 Pump Application 17
5.10 Pump Performance Testing 28
5.11 Pump Troubleshooting 30
6.0 NUCLEAR CONSIDERATIONS 32
7.0 UTILITY EXAMPLE EXERCISES AND SOLUTIONS 32
7.1 Exercise No. 1 (Hotwell Pumps) 32
7.2 Exercise No. 2 (RHR Pumps) 35
7.3 Exercise No. 3 (Reactor Coolant Pumps) 36

EPRI Licensed MaterialMechanical Series, Module 4 Centrifugal Pumps
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8.0 SOURCE DOCUMENTATION 37
9.0 INDUSTRY OPERATING EXPERIENCE 37
10.0 PROFICIENCY MEASURES 38
10.1 Proficiency Measures (Questions) 38
10.2 Proficiency Measures (Solutions) 40

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1.0 SCOPE AND PURPOSE
The purpose of this training module is to provide the principles and description of the theory ofoperation of various types of centrifugal pumps. This module will also provide understanding ofpump selection, installation, testing, and failure modes
2.0 SUGGESTED PRIOR SKILLS AND KNOWLEDGE
It is suggested that the student review the basic engineering principles of fluid flow, head loss inpiping systems, and fluid properties such as specific gravity.
3.0 OBJECTIVES
The objectives of this module are to provide the student with an understanding of centrifugalpumps including the following:
Describe types and typical application of pump types. Define/Describe:
Best Efficiency Point Cavitation Head vs. Resistance Runout Gas Binding (causes and effects) Miniflow purpose
Describe the effect of parallel vs. series operation. List typical methods for performance testing. Describe the limitations of shop curves (water density, motor speed, casing differences). Define/Describe typical mechanical failures and mitigation strategies. With a given set of conditions (system resistance, head curve, temperature, suction
pressure), evaluate for: NPSHA Cavitation potential Miniflow adequacy Runout potential Efficiency Pump to pump interaction potential

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4.0 NOMENCLATURE
BEP = Best Efficiency PointBHP = Brake HorsepowerD = Impeller Diameter feetEFF, pump = Pump EfficiencyH = Head (feet)N = Shaft Speed (revolutions / minute)Ns = Specific SpeedNss = Specific Suction SpeedNPSH = Net Positive Suction Head (feet)SG = Specific GravityQ = Flow (Gallons / minute)WHP = Water Horsepower
5.0 PRINCIPLE AND PROPERTIES
5.1 Pump Types
Pumps can be classified into two categories based on the method by which pumping energy istransmitted to the fluid. These categories are kinetic and positive displacement pumps. Mostkinetic pumps are centrifugal pumps. Liquid flowing into the suction side or inlet of acentrifugal pump is captured by the impeller and thrown to the outside of the pump casing orvolute. The volute converts the velocity imparted to the fluid by the impeller into pressure.
Centrifugal pumps are divided into the following: Single and multistage volute types with single and double suction impellers Multistage diffuser types with single suction impellers
These are further divided into: Radial or vertical split or Axial or horizontal split case types
Volute type pumps are further divided into: Single Volute Double volute
All casings of the radial or vertical split have the casing split at right angles to the shaftcenterline, whereas, the horizontal split case is parallel to the shaft centerline.
A single volute pump, Figure 1, has one channel that increases in cross section therebyconverting the kinetic energy into pressure. At the best efficiency point (BEP) the pressureson opposite sides of the impeller are essentially equal. However, at partial flows the pressures

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are not equal and could be sufficiently large enough to cause excessive deflection of the shaft,especially in high head pumps.
Figure 1: Single Volute Pump
To minimize this deflection a double volute pump is used, Figure 2. A second channel is castinto the pump casing which equalizes the pressures across the impeller better. The doublevolute provides similar flow channels with outlets 180 degrees apart, which result in aconsiderable reduction in the radial loads on the shaft.

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Figure 2: Double Volute Pump
In a diffuser casing, Figure 3, the vanes are designed to form passages of gradually expandingarea to insure a uniform decrease in velocity from inlet to outlet. The multiple passagesequalize the pressure at all points about the periphery of the impeller resulting in perfect radialbalance.

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Figure 3: Diffuser Pump
There are two basic elements of the centrifugal pump. They are the stationary element and therotating element. The stationary element consists of the pump case, baseplate, stuffing boxesand bearings. The stationary element provides the support and enclosure for the rotatingelement. The case provides the suction and discharge nozzles and directs the flow of liquidinto and away from the impeller. It converts kinetic energy generated by the impeller intopotential energy (pressure). The rotating element consists of a shaft on which is mounted oneor more impellers. The rotating element is the means to generate the flow of liquid and therequired head of the pump.
5.2 Impeller Types
Impellers can be classified as either single or double suction, with either being enclosed, semi-enclosed or open, Figure 4. The terms single and double suction only designate the numberof inlets contained in the impeller.

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Figure 4: Impeller Configurations
Enclosed Semi-Enclosed Open
A single suction has one inlet, Figure 5, and a double suction has two inlets, Figure 6.
Figure 5: Single Suction Impeller
Impe
ller
Dia
met
er
Wear Ring Hub
Suction Vane Edge
Shroud
Discharge Vane Edgeor Tip
Eye
Dia
met
er
Suction Eye

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Impe
ller
Dia
met
er
Eye
Dia
me
ter
Figure 6: Double Suction Impeller
Wear Ring Hub
Suction Eye
Suction Vane Edge
Shroud
Discharge Vane Edgeor Tip
A closed impeller, has a side wall (called shrouds) on both sides of the impeller. A closedimpeller will have a wear ring on each side of the inlet to reduce leakage from the dischargeback to the suction.
A semi-closed impeller has a shroud on one side of the vanes and the other side is left open.These types of impellers are not furnished with wear rings and the losses from leakage fromthe discharge to the suction are higher than a closed impeller.
The open impeller has cast vanes without any shrouds. Its efficiency is low and its use inpower plants is limited.
5.3 Pump and Head Terminology
The term head is used as a measure of energy and has the units of feet.
Recall from the incompressible flow module that friction head (hf) is the energy required toovercome resistance to flow in the pipe, fittings, valves, entrances and exits.

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Eq. 1
Velocity head (hv) is the energy of a fluid as a result of its kinetic energy.
Eq. 2
Pressure head (hp) is the pressure of the fluid being pumped. Eq. 3
Static suction head (hs) is the vertical distance in feet above the centerline of the pump inlet tothe free level of the fluid source. If the free level of the fluid source is below the pump inlet,hs will be negative and is referred to as static suction lift.
Static discharge head (hd) is the vertical distance in feet above the pump centerline to the freelevel of the discharge tank.
Net suction head (Hs) is the total energy of the fluid entering the pump inlet. It includes thestatic suction head (hs), plus the pressure head (if any) in the suction tank (hp), plus thesuction velocity head (hv), minus the friction head (hf) in the suction piping. See Figure 7.
Eq. 4
cf
Dg
fLevh
2
2
=
cv
g
vh
2
2
=
p
hp =
fps s h h h H +=

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Figure 7: Net Suction Head
p,hp
hs
Example 1
Assume velocity is negligible, pressure in tank = 100psig, elevation difference = 20ft, frictionalhead loss = 8ft.
ftH
ftpsi
ftftH
s
s
277
831.2)7.14100(20
=

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