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Transcript of Centrifugal Pumps
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
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?
Fig.1.1. Process with centrifugal pump (principle)
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)
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.
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.
Fig.3.5. Priming of pump (principle)
Fig.3.1. Single-stage centrifugal pump (principle)
Fig.3.3. Multi-stage centrifugal pump (principle)
Fully fluidfilled casing!
Pinlet > 0 = Flooded inletPinlet < 0 = Suction lift
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)
Pressure increaseduring stages!
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.
Fig.4.1. Main pump parts (principle)
Fig.4.3. Impeller types/design (principle)
Fig.4.5. Mechanical shaft seal (flushed seal principle)
Fig.4.2. Pump casing/port orientation (principle)
Fig.4.4. Mechanical shaft seal (single seal principle)
Fig.4.6. Base-mounted pump (principle)
Motor shaft/pump shaft
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 1.6m (64Ra) or 0.8m
(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.
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)
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 boo