monitoring pump performance with vibrationfhegedus/vibrationmonitoring/ali parhizkar... ·...

Monitoring Pump Performance with Vibration

Mitchell Stansloski, PhD, PE

Centrifugal Pumps

Centrifugal pumps

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Volute Centrifugal Axial Flow

Centrifugal Pumps (Radial Flow Pumps): A pump using radial flow impellers that give their energy to fluid primarily by centrifugal force

Centrifugal pumps


• Higher pressure, lower flow compared to axial flow• Impeller adds energy to fluid by increasing velocity• Volute (where fluids goes out—expansion cavity) converts velocity into pressure

Basic Pump Operation

Operating range given by intersection of system and pump curves.

Pump Curve with Power and Efficiency

System Curve

Pump friction and head losses.

Pump Flow Control

Various ways to control pumps.

Pump Curve vs. Impeller

Pump curve showing different impeller sizes.

Pump Curve vs. RPM

Pump curve showing different speeds.

Pump Curve and Vibration

Centrifugal pump severity


Volute Centrifugal Axial Flow Centrifugal

Machine Displacement (mils, p-p)

Velocity (ips, pk)

Acceleration (g, pk)

Rigid mounted centrifugal

NA 0.05 - 0.25 0.5 – 1.5

Resilient mounted centrifugal

NA 0.10 – 0.50 0.5 – 1.5

Two Types of Pump Vibes

• Periodic– Vane passing frequency– Shaft/Coupling/Impeller Unbalance

• Random– Cavitation– Turbulence

• Pump performance directly affects both!!

Signal Processing Warning

• Changing resolution directly affects random vibration amplitude

Pump Performance and Vibration Frequencies

• Periodic – Vane passing frequency– Load

• Random – Cavitation and Turbulence– Efficiency

Centrifugal pumps


Vibration Diagnostics:

•Each time blade passes an arbitrary point on pump, it generates a small vibration•Load on pump directly changes amplitude of VPF—can detect problems (like blocked suction or discharge)

Vane Pass Frequency: Vibration caused by movement of each blade in a pump or fan

Centrifugal pumps


Vibration Diagnostics:Poor Installation: Application of extra force on suction and discharge flanges to align and mate flanges

• Extra force on pump housing—can distort housing•Distortion causes hydraulic unbalance

•Can cause high 1X running-speed and VPF vibrations

Pipe Design

http://www.chemicalprocessing.com/articles/2004/218/

Centrifugal pumps


Vibration Diagnostics:Cavitation: Implosion of air bubbles in and around impeller of pump

• Occurs when net positive suction head is too low:

•Net Positive Suction Head Required (NPSHR): pressure of fluid at inlet in order satisfy the rated output and overcome frictional or shock losses

•Net Positive Suction Head Actual (NPSHA): Actual positive suction head—determined by system feeding the pump (piping, level of inlet reservoir, etc.)

•If NPSHA insufficient:•Some fluid vaporizes upon entrance to pump housing•Vapor bubbles collapse violently near impeller

•Cause excessive damage and corrosion (throw fan out of balance)

Centrifugal pumps


Vibration Diagnostics:Identifying Cavitation:

1) Random2) Broad-band (over large frequency range)3) High frequency (30,000 cpm to 120,000 cpm)

--Think of it like implosions act like many tiny hammers that ring natural frequencies of pump housing

Centrifugal pumps


Vibration Diagnostics:•Eliminate Cavitation: 1) Reduce NPSHR

2) Increase NPSHA

•Reduce NPSHR: 1) Restrict discharge 2) Over-size pump3) Use impeller with larger eye (inlet)

--ALL affect efficiency so be careful!

•Increase NPSHA: 1) Raise height of source fluid2) Lower pump3) Reduce pipe friction4) Pressurize supply tank5) Reduce pump speed

--ALL affect efficiency so be careful!

Pump Cavitation

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CHW Secondary Pump 1\ Pump\ OB V\ Std Vel Meas\ Spec trum 12/ 13/ 2011 11:33:55 AM

12/ 13/ 2011

3/ 29/ 2012

4/ 30/ 2012

M

f [cpm]

v op [inch/ s]

RPM : 1780 (29.67Hz)M(x) : 120.00 cpm (0.07 Orders)M(y) : 0.02141 inch/ s

Pump Cavitation


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Tertiary CHW Pump 1\ Pump\ IB V\ Std Vel Meas\ Spec trum 4/ 30/ 2012 9:20:54 AM

2/ 15/ 2011

3/ 29/ 2012

4/ 30/ 2012

f [cpm]

v op [inch/ s]

RPM : 1780 (29.67Hz)

Cavitation Improved


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FHX CW Pump\ Pump\ IB A\ Std Vel Meas\ Spec trum 1/ 25/ 2012 8:20:03 AM

10/ 13/ 2011

12/ 13/ 2011

1/ 25/ 2012

f [cpm]

v op [inch/ s]

RPM : 1780 (29.67Hz)

Centrifugal pumps


Vibration Diagnostics:Turbulent Flow: Irregular motion of fluid particles in directions transverse to the direction of the main flow

• Occurs when poor piping or recirculation cause rough flow of fluid through pump

•Poor Piping: Should be at least 10 diameters of constant geometry pipe before and after pump

•Recirculation: Amount of discharge is too high for outlet piping, fluid will return to volute causing turbulence in housing

• Random, broad-band vibrations at low frequencies

Using Vibration to Set Performance

• Cascade Plot– Monitor broadband vibration FFT spectra versus

RPM

• Waterfall Plot– Monitor broadband vibration FFT spectra versus

valve position

Single Channel Signal Processing


Cascade Plot: Series of spectra as machine speed varies

Cascade Plot

Pump Performance

http://www.emeraldinsight.com/journals.htm?articleid=843213&show=html

Summary

• Periodic vibration (vane passing frequency)– Indicates pump load

• Random vibration (cavitation & turbulence)– Indicates pump efficiency

• Cascade and Waterfall Plots – Vibration vs. RPM or valve position– Easily identifies changes in both

monitoring pump performance with vibrationfhegedus/vibrationmonitoring/ali parhizkar... ·...

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