Behind Pump Vibrations

8/8/2019 Behind Pump Vibrations

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The reasons pumps shake


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SWIPE PUMP ARCHIMEDES SCREW


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MULTISTAGEHORIZONTALS MULTISTAGE VERTICALS


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impeller

shaft

Wear rings

Shaft

sleeve

Pump case

bearings

Mechanicalseal

packing


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Inbalance, Bent shaft (1x RPM)

Misalignment ( 2xRPM)

Vane Pass (# of impeller vanes x RPM )

Cavitation ( Raised Floor )

Rubbing ( .5x RPM )

Looseness ( multiples of RPM)

Roller Bearing Damage ( high frequencies ) High Axial ( Off design operations )


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Common Causes Wear

Inadequate balance criteria

Inadequate shaft TIR criteria Improper shaft materials

Rotor grab


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Operational Cause Off flow operation


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SINGLE VOLUTE TWIN VOLUTE


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Common Causes

Inadequate alignment procedures

Thermal growth

Pipe loading Inadequate base-plates and grouting


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P1/rg+v12/2g+z1=P2/rg+v22/2g+z2+h+w-q Bernoullis equation equates the energy at two

points in time

Its importants in this class is how it relatespressure and velocity


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Assuming a particle of water entering an

impeller. Time one will be in the suction lineand time two will be as it enters the impeller.

P1/rg+v12/2g+z1=P2/rg+v2

2/2g+z2+h+w-q

Leaving P1/V12=P2/V22 or P1/P2=(V1/V2)2

There fore as velocity increases pressure dropsby the square


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There are two primary types of cavitation and

they are caused by very different conditionsand in different areas of the impeller. They areboth accompanied by a sound similar to the

pump trying to pump marbles


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This is the cavitation most of think about when

they hear the term. It is caused by too lowsuction pressure to at the suction of theimpeller such that when the impeller inlet vanehits the liquid it momentarily drops below the

vapor pressure . This damage is found on thevisible side of the inlet vane usually in the rootor spread across the inlet vane. This type of

cavitation is usually more severe in high flowcondition, as the inlet velocity of the fluidincreases.


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Recirculation Cavitation is found at low flow

conditions. This type of cavitation is due toturbulents in the impeller caused by liquidtrapped in the impeller with no place to go

due to the reduced flow. The damage for thiscavitation is found on the back side of theimpeller inlet vane and is sometimes missed

until holes are found in the vanes.


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Common Causes Improper installation Misalignment

Pipe strain


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Improper installation

Reusing bearings Improper lubrication

Defective new bearings


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Knowing why certain types of vibration are

present can help you know how serious theproblem is and how it can be resolved.


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Behind Pump Vibrations

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