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Pump RCF Analysis

Reed critical frequency

Vibration analysis (Reed Critical Frequency) of Vertical Turbine Pump
1 Background

Vertical pumps (specifically vertical turbine pumps) are tall cantilever type structures that have mechanical natural frequencies (MNFs) which can occur at pump run speed creating resonant vibration conditions. These natural frequencies are also called reed critical frequencies (RCFs) due to the mode shape being like a musical reed vibration shape (cantilever mode). If the pump motor combination reed critical frequency occurs in the speed range of the pump, high vibrations can occur.

RCF analyses can be performed at the design stage for new pump-motor combinations, field installed revamps, or problematic installations already out in the field.

2 Scope

The scope of an RCF Analysis includes creation of a finite element (FE) model of the pump head from foundation up, including the motor. A simulation is performed to determine the expected RCF and, if necessary, the pump speed ranges to avoid.

In special cases the pump impeller bell housing assembly can also be modeled to determine its respective MNF, although in most cases this is not necessary.

Onsite field testing can also be completed to determine ‘as installed’ RCF values, and measure the actual resulting vibration levels.

Vertical Turbine Pump Coupling

Additional scopes can include:

  • pump head nozzle load calculations
  • foundation load calculations
  • seismic calculations
  • anchor bolt operating load calculations
  • lifting lug analysis
  • torsional analysis
  • lateral analysis
3 Wood Group Advantages
  • Industry leading finite element analysis (FEA) experts provide fast and accurate results.
  • Technical review for improved quality control by Principal Engineers ensures that appropriate boundary conditions and sound engineering techniques are used on your project.  
  • Experienced field engineering team can support you globally to provide onsite testing and verification of vibration and stress.
4 Keywords
  • Reed critical frequency (RCF)
  • Cantilever Vibration Mode
  • Vertical Turbine Pumps
  • Vertical Can Pumps
  • 1st Mechanical Natural Frequency, or First Mechanical Natural Frequency (MNF)

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