1. Why is it important to know about centrifugal pumps? 2 2. Who should know about centrifugal pumps? 4 3. The principle of a centrifugal pump 5 4. Typical parts in a centrifugal pump 7 5. Sanitary centrifugal pumps 9 6. Typical range of centrifugal pumps 11 7. Centrifugal pump selection 13 8. Installation 15 9. Operation and service 17 10. Troubleshooting 19 Glossary 21 Other handbooks in this series 23

Contents

1

Centrifugal pumps

The various aspects of centrifugal pumps are very important to consider when dealing with flow technology and flow equipment. Understanding the aspects of centrifugal pumps makes it easier to select correct pumps, optimize processes and minimize costs.

1. Why is it important to know about centrifugal pumps?

2

Fig.1.1. Process with centrifugal pump (principle)

CIP

Milk

CIP

Milk

A centrifugal pump is typically the most common sanitary pump type used in sanitary processes. Benefots include a relatively low purchase cost, wide selection, simple design and easy maintenance.

Examples of centrifugal pumps 1. A centrifugal pump is used in processes with non-viscous and non-

particulate fluids, e.g. beer, CIP, cream, milk, soft drink and purified water.

2. There are typically many types of centrifugal pumps available for various types of applications.

3. The main parts of a centrifugal pump are motor, shaft, adapter, shaft seal, impeller, casing and seals.

4. A centrifugal pump is typically selected from a pump curve or a pump selection program.

Fig.1.2. Centrifugal pump types (principle)

Fig.1.3. Centrifugal pump design (principle)

Fig.1.4. Centrifugal pump selection (principle)

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Standard High-cleanMulti-stage

Casing

Impeller

Shaft

Shaftseal

AdapterMotor

It is important that the target group knows the various aspects of centrifugal pumps, including principle and design, available types, selection, suitability and limitations related to given processes. This ensures that processes are optimised and that errors, damage and personal injuries are avoided. The target group includes: 1. Process designers, who should know what centrifugal pump types and

configurations to select so that the process is optimised related to quality and costs.

2. Sales and sales support people, who should know the possibilities and limitations of centrifugal pumps related to applications/processes in question.

3. Field operators, who should know the possible causes of centrifugal pump malfunction and know how to solve them.

4. Beginners in the flow industry, who should have a basic understanding to work efficiently.

2. Who should know about centrifugal pumps?

All people in touch with flow equipment during its life cycle should know about centrifugal pumps.

4

General principle: • Fluid enters the pump casing and impeller center and is forced into a

circular movement by the impeller vanes and the centrifugal force. The fluid thus leaves the casing with increased pressure and velocity.

• Typically suitable for low viscous, non-particulate and non-aerated fluids such as beer, CIP, cream, juice, milk, soft drinks, water etc.

Single-stage principle: The fluid inlet, the built-up of velocity and pressure and the fluid outlet all happens in one stage (one casing and one impeller). Multi-stage principle: • Fluid enters the pump casing and impeller center, and fluid pressure and

velocity are built up in the first stage (casing and impeller) similar to the single-stage pump.

• Fluid with increased pressure and velocity is directed to the second stage (casing and impeller), where the fluid pressure and velocity is further increased.

• The result is a pressure increase (boost) in each stage, where the total pressure increase depends on the number of stages in the pump.

• Typically available with 2-4 stages. Priming of a centrifugal pump: • The pump casing should always be filled with fluid before starting the

pump to ensure correct operation. • The pump can operate with a positive inlet pressure (flooded inlet) or

with a negative inlet pressure (suction lift). • For suction lift, fluid can remain in the pump casing by using a non-

return valve in the suction line.

3. The Principle of a centrifugal pump

The centrifugal pump transfers fluid at a certain capacity from one point to another in a process. The pump builds up fluid pressure to overcome losses in the process. Capacity and pressure are created by the rotating impeller inside the pump casing.

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Fig.3.5. Priming of pump (principle)

Fig.3.1. Single-stage centrifugal pump (principle)

Fig.3.3. Multi-stage centrifugal pump (principle)

Several stages(casings/impellers)

Fluidin

Fluidout Stages

2 1

Fully fluidfilled casing!

Pinlet

Pinlet > 0 = Flooded inletPinlet < 0 = Suction lift

Flow/pressure

1

2

3

Rotatingimpeller

Casing

Fig.3.6. Priming of pump for suction lift (principle)

Fig.3.2. Single-stage centrifugal pump (principle)

Fig.3.4. Multi-stage centrifugal pump (principle)

Casing

Fluidin

Fluidout

Rotatingimpeller

Fluidin

Fluidout

Stage/casing2 1

Pressure increaseduring stages!

Rotatingimpellers

6

4. Typical parts in a centrifugal pump

Typical main pump parts:

Main pump part Description/function Casing/backplate • Contains impeller where fluid is transferred

from inlet to outlet. • Includes inlet and outlet ports. • Typically flexible port orientation. • Typically fitted to an adapter.

Shaft • Rotates impeller which is fixed to it. • Is fixed to the motor and rotates with it.

Impeller • Transfers fluid from inlet to outlet with increased capacity and pressure.

• Is fixed on the shaft and rotates with it. • Typical types are open, semi-open or

closed. Shaft seal • Seals between rotating shaft and stationary

casing. • Typically a mechanical seal, external or

internal. • Typically available as single, single flushed

and double flushed seal. Adapter • Fixes pump casing to the motor. Motor • Rotates shaft (impeller) which is fixed to it.

• Typically a 3-phase electrical motor. • Typically available for various electrical site

supplies (voltage and frequency). • Typically available in various protection

classes (flameproof etc.). Other parts Seals, motor cover, seal flushing, coupling/

base (base-mounted pump). Typical materials • Steel parts of 316L or 304 stainless steel.

• Elastomers of NBR, EPDM, FPM, PTFE.

A centrifugal pump is a relatively simple pump. Design, types and numbers of parts vary depending on centrifugal pump brand, type and configuration.

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Fig.4.1. Main pump parts (principle)

Fig.4.3. Impeller types/design (principle)

Fig.4.5. Mechanical shaft seal (flushed seal principle)

Casing

Impeller

Shaft

Shaftseal

AdapterMotor

Fig.4.2. Pump casing/port orientation (principle)

Fig.4.4. Mechanical shaft seal (single seal principle)

Fig.4.6. Base-mounted pump (principle)

CouplingMotor

Base

Casing

Motor shaft/pump shaft

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5. Sanitary centrifugal pumps

Large radii and clearances: • Use large radii on corners to ensure easy cleaning. • Use large clearances to ensure good fluid and cleaning flow. • Critical areas are welds and connections in general, porting and shaft

seal areas. Drainage: • Drainage ensures that the pump can be emptied completely so that

there are no remains (no “sump”) of processed fluid or cleaning agents. • Drainage is typically achieved through a drain fitted on the bottom of the

pump casing or by rotating the casing outlet so that fluid can drain from it.

• The critical area is the bottom of the pump casing. Minimum elastomer usage: • Elastomers wear down over time and can cause contamination.

Therefore, elastomer usage and elastomer surface exposed to fluids should be minimised.

• If possible, seals should be designed with fixed compression. Seal contraction/swelling due to fluids/temperature should be minimised.

Correct materials and surface finishes: • Typical materials for fluid-contact parts are 316L stainless steel and

various elastomer grades. Elastomers are often FDA-compliant. • Typical surface finishes of fluid-contact parts are 1.6μm (64Ra) or 0.8μm

(32Ra), normally machined or polished.

A sanitary centrifugal pump is designed according to given hygienicstandards. This includes easy cleanability and use of correct materials for internal pump parts.

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Fig.5.1. Large radiis (principle) Fig.5.2. Large clearances (shaft seal principle)

Fig.5.3. Drainage (principle) Fig.5.4. Minimum elastomer usage (principle)

Fig.5.5. Correct materials and surface finishes (shaft seal principle)

Wrong! Correct!

ImpellerFluidarea

Seal

Impellernut

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Standard pump: • For most applications, typically with max. system pressure of 10 bar

(147 psi). • Typically available in many sizes to cover a wide range of duties. High-pressure pump: • For example for filter applications, typically with max. system pressure of

approx. 40 bar (588 psi). • Typically with a heavy casing/backplate design, with internal shaft seal

and special motor (bearings) to withstand high inlet/system pressures. Multi-stage pump: • Working as pumps coupled in series. Typically a booster pump for high

pressure at relatively low capacity. • Typically with a heavy casing/backplate design, with internal shaft seal

and special motor (bearings) to withstand high inlet/system pressures. Self-priming pump: Working as a liquid-ring pump for aerated fluids, such as CIP return. High-clean pump: • For pharmaceutical or similar applications with demand of increased

cleanability. • Typical design features are 45° casing outlet, casing drain, flushed shaft

seal, polished surface finish and material traceability. Pumps with typical optional equipment: • Pump with heating/cooling jacket, fitted to pump casing to either heat

viscous fluids or to cool heat-sensitive fluids. • Pump with inducer fitted to the impeller to increase suction capability.

6. Typical range of centrifugal pumps

A centrifugal pump is typically available in many types and configurations to fulfil most process demands. This includes standard pump, high-pressure pump and high-clean pump. The available types depend on the pump brand.

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Fig.6.1. Standard pump (principle)

Fig.6.3. Multi-stage pump (principle)

Fig.6.4. High-clean pump (principle)

Flushedseal

Casingdrain

45o casingoutlet

Heavy casing/backplate

Internalshaft seal

Specialmotor High

pressure!

Fig.6.2. High-pressure pump (principle)

Highpressure!

Specialmotor

Internalshaft seal

Heavy casing/backplate

Fig.6.5. Pump with heating/cooling jacket (principle)

CasingHeating/coolingjacket

Heating/coolingsupply

Heating/coolingsupply

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Determine process type: • “Standard” sanitary or high-clean process? • High inlet pressure or booster process? • Influences the selection of pump type (standard, high-pressure, high-

clean etc.). Collect fluid data: • Such as type, temperature, viscosity, abrasives, solids etc. • Influences the use of shaft seal type and seal face material. • Influences selection of elastomers and surface finish (often preference). Collect performance/site data: • Such as capacity, inlet pressure, head, NPSHa, and risk of cavitation. • Such as voltage supply, frequency, and installation conditions. • Influences the pump and motor size, shaft seal and motor type. Pump selection/configuration: • Select suitable pump configuration according to guidance shown and

according to recommendations of pump suppliers. • Select/size suitable pump from pump curve or pump selection program. • Ensure correct pump/motor type, size, porting, shaft seal, surface finish

and elastomer grade.

7. Centrifugal pump selection

A successful centrifugal pump operation very much depends on correct pump selection. It is important to get all necessary process and site data, as well as customer preferences to ensure correct pump selection.

Q

H

Pump curve

Process curve

D1D2D3

QD

HD

Fig.7.1. (Selection principle) The pump is sized by using the pump duty (QD,HD) in the pump curve. Correct pump/impeller size is the intersection point between the process and pump curves.

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Fig.7.2. Centrifugal pump selection process (guidance only)

SELECTION:

Check process and customer demands

Get porting/ connection data

3. Size, orientation, standard?

Check process and customer demands

4. Machined, polished, electro-polished, other?

Get surface finish

6. Get elastomer grade

- Check compatibility - Check with pump suppliers

NBR, HNBR, EPDM, FPM, PTFE, other

Get performance/ site data: - Capacity? - Head? - NPSHa? - Voltage? - Frequency? - Other?

2. High inlet pressure? - Pump with internal shaft seal (if possible) - Shaft seal with hard face material - Motor with special bearing design - Special combination

of voltage/frequency? - Flame-/explosion hazard?

Special electric motor

5. Get shaft seal configuration

- Check compatibility - Check with pump suppliers

- Non-mechanical/ mechanical seal? - External/internal seal? - Single seal? - Single flushed seal? - Double flushed seal?

- High-pressure pump - Multi-stage pump

High pressure/booster?

1. Standard pump

Self-priming pump

Standard sanitary?

Get process/ fluid data: - Fluid type? - Viscosity? - Density? - Temperature? - Particles? - Concentration? - Other?

Aerated?

High-clean pump Purified water, WFI etc?

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8. Installation

Pump/piping alignment: • Align pump/piping – and support piping so pump casing is not stressed. • Stressing of the pump casing can cause seal leakage and cause metallic

contact between impeller and casing so that the parts are damaged. • Align pump/motor/coupling carefully (for base-mounted pump). Vibration and thermal expansion: • Compensate for vibration and thermal expansion of long piping, for

example by installing compensators between the pump and piping. • Vibration and thermal expansion can stress the pump casing and cause

shaft seal leakage and damage casing, shaft, shaft seal and impeller. Seal flushing supply: • If fitted, connect and supply flushing fluid for a flushed shaft seal

correctly according to instructions. Ensure correct fluid type, flow and pressure.

• Supply fluid before starting the pump and disconnect fluid supply after stopping the pump.

Electrical supply: • Connect and supply electricity to the motor according to instructions. • Ensure that motor data are in accordance with given site electrical

supply (voltage and frequency). • Before use, check the pump after installation to ensure smooth operation

and correct rotation of direction of the impeller. Priming of pump: • Ensure that the pump casing is filled with fluid before starting. • Check the installation/suction conditions to ensure that available suction

pressure (NPSHa) is higher than required (NPSHr) from the pump. This minimises the risk of cavitation.

A centrifugal pump should always be installed correctly according to given instructions from the pump supplier. This ensures correct pump operation and it minimises risk of pump damage and possiblepersonal injuries.

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Fig.8.1. Pump/piping alignment / support (base-mounted pump principle)

Fig.8.2. Vibration and thermal expansion (principle)

Fig.8.3. Seal flushing supply (principle)

Fig.8.4. Electrical supply (principle)

Fig.8.5. Priming of pump (principle)

Correct sealflush data!

Start/stop fluidflow correctly!

ImpellerVoltage?

Frequency?

Correct directionof rotation!

Fully fluidfilled casing!

Sufficientinlet pressure!

Pinlet NPSHa > NPSHr ⇒ No cavitation!

Align pipingand casing!

Supportpiping!

Align casingand motor!

CouplingMotor

Base Casing

Compensatevibration/thermal

expansion!

Compensator

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Pump operation: • Prior to use, check the pump after installation to ensure smooth

operation and correct direction of rotation of the impeller. • Start and stop the pump carefully. Use soft starter or frequency

converter if required of the motor or process. • Pay attention to moving parts and hot equipment. • Pay attention to possible leakage from the shaft seal. • Never throttle/block both suction and discharge sides of the pump. Pump cleaning: • Handle cleaning agents according to instructions; use protective gloves

and goggles. • Clean frequently according to instructions. • Pay attention to hot equipment, hot cleaning agents/water and possible

steam supply. • Pay attention to possible leakage from the shaft seal. • Use flushed shaft seal to clean seal faces from sticky and crystallising

fluids. Pump service: • Disconnect fluid supply/pressure and electrical supply before service. • If fitted, disconnect seal flushing supply before service. • Pay attention to moving parts and hot equipment. • Service and replace parts according to instructions and regulations. • Before use, check the pump after service to ensure smooth operation

and correct direction of rotation of the impeller.

9. Operation and service

A centrifugal pump should always be operated and serviced correctly according to given instructions from the pump supplier. This ensures correct pump operation and best process quality and it minimises risk of pump damage and possible personal injuries.

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Fig.9.3. Centrifugal pump cleaning (principle)

Fig.9.5. Centrifugal pump service (principle)

Replacewear parts!

Shaftseal

Casinggasket

Fig.9.1. Centrifugal pump operation (principle)

Fig.9.2. Centrifugal pump operation (principle)

Fig.9.4. Centrifugal pump cleaning (flushed shaft seal principle)

Leakingcleaning agent!

Hotpump/line!

Shut-offvalve

Flowin

Flowout

Never blockboth lines!

Flow meter Frequency

converter

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General information: • Good description of pump failure and process, get sketches and

possible worn parts, if possible. • Check and compare nominal/original process conditions with actual. • What has changed in process since satisfactory operation?

• Has the pump been undergoing recommended/routine maintenance?

• Have any spare parts been replaced on the pump?

• When was the last maintenance of the pump? • How was the condition of internal pump parts?

• How long did the pump operate satisfactorily before failure?

Most common pump failures:

Failure Possible cause/remedy Shaft seal leakage

• Incompatible seal/fluids, cavitation/vibration, temperature, pressure, incorrect installation or service, dry running.

• Check compatibility and pump instruction manual. Noise and vibration

• Cavitation, worn parts, misalignment. • Check process, pump parts and installation.

High power consumption

• Worn pump/motor, high capacity, high viscosity/ density.

• Check pump/motor, pump duty and process. Loss of capacity • Incorrect impeller rotation, high viscosity.

• Check rotation and process. Loss of suction • Low NPSHa, aerated/blocked suction line, high

viscosity, incorrect impeller rotation, worn parts. • Check process and pump parts.

Fast wearing • Incompatible pump parts/fluids, cavitation/vibration, temperature, pressure, incorrect installation or service, dry running.

• Check compatibility and pump instruction manual.

10. Troubleshooting

It is important to get all necessary pump and site installation data/information to ensure correct identification of a pump failure. This ensures that the pump failure is solved fast and efficiently.

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Fig.10.1. Leaking shaft seal (principle)

Fig.10.5. Loss of suction (principle)

Fig.10.3. Overloaded motor (principle)

Noise! Vibration!

Highcurrent!

Hotmotor!

Meter

Fig.10.2. Noise and vibration (principle)

Fig.10.4. Loss of capacity (principle)

Fig.10.6. Worn shaft seal part (principle)

Impeller

Check impellerrotation!

Noflow!

Check for airin casing/line!

Nosuction!

NPSHa > NPSHr

Check impellerrotation!

Source: Burgmann

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Aseptic Process and component design which ensures that there is no increase of bacteria content in the processed fluid.

Capacity The maximum volume of fluid that can pass a

certain area per unit of time. CIP Cleaning In Place (cleaning without dismantling

equipment first). Double seal A flushed (water or similar) shaft seal with

mechanical seal faces on both the pumped fluid side and on the flushing side.

Dry running No pumped fluid between seal faces. Will quickly

wear down the seal faces due to excessive heat. Elastomer Non-metallic sealing part with elastic properties, e.g.

natural or synthetic rubber. External seal Seal design where most rotating seal parts are

outside the pumped fluid. The most common seal type.

Flooded inlet Positive inlet pressure/head. Flow equipment Equipment used in flow systems. Examples are heat exchangers, pumps, valves, tubing, fittings and tank parts. Fluid Liquids/media (non-solid and non-gas) processed in flow system. Flushed seal External (water or similar) flushing arrangement,

typically used to cool or clean the seal faces. Frequency converter Electronic device to regulate speed of an electric

motor. Common and economical way to control pump performance.

.

Glossary

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High purity Process with special cleanability demands. The term is typically used within the pharmaceutical industry. Impeller Mechanical pump part fitted on the pump/motor shaft. The rotating impeller (vanes) converts fluid velocity to fluid pressure. Inlet pressure Fluid pressure entering the pump inlet. Will affect

the seal faces. Internal seal Seal design where most rotating seal parts are

inside the pumped fluid. Suitable for high pressure. Mechanical seal Shaft seal where seal faces (sealing interface)

consists of a stationary and a rotating mechanical seal part.

Non-mechanical seal Such as packed gland, typically used for industrial

(non-sanitary) types of applications. NPSH Net Positive Suction Head. NPSHr Required minimum pressure in suction line to avoid cavitation. NPSHa Available suction pressure at actual process conditions. Pressure Force per unit area. Suction lift Negative inlet head/pressure. Viscosity Specifies how “thick” or “thin” a fluid is.

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Other handbooks in this series

1. Pressures in flow systems 2. Cavitation 3. Fluid properties 4. Pumps for sanitary processes 5. Centrifugal pumps 6. Sizing centrifugal pumps 7. Rotary-lobe pumps 8. Sizing rotary-lobe pumps 9. Pump motors 10. Pump-shaft seals 11. Troubleshooting pumps 12. Flow control 13. Materials for flow equipment 14. Valves for sanitary processes 15. Single-seat valves 16. Mix-proof valves 17. Regulating valves 18. Troubleshooting valves 19. Valve automation 20. Standards and regulations