behind pump vibrations
Post on 10-Apr-2018
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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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