Vibration readings

VIBRATION READINGS V018

You can read the vibration a variety of ways:

  • Frequency
  • Amplitude
  • Velocity
  • Acceleration
  • Spike Energy
  • Acoustic emissions
  • Deflection

Many systems read vibration by recording acceleration. The problem with this method is that if you do not know the frequency the readings are not very meaningful. Because of this most systems read an average of all of the frequencies involved and recommend taking action when this average reading doubles in a particular location. If bearings are your primary concern high and low electronic filters can be used in some equipment to filter out frequencies below 55 Hz. and above 2500 Hz. These filters will help the operator zero in on those frequencies normally associated with bearing problems.

Unfortunately, most vibration data references bearing operation. There is little to no information available about mechanical seal vibration modes. The problem is further compounded by:

  • The large variety of seal materials in use.
  • Major differences, in design between popular brands of single and multiple seals.
  • Availability of vibration damping in these designs.
  • The wide spread use of environmental controls.
  • The variety of fluids we find surrounding mechanical seals.

The vibration readings almost always means that the equipment has started to destroy its self. Most companies are trying to collect enough data to predict the remaining life before total destruction takes place.

The obvious solution to all of this is to adopt good maintenance practices that will eliminate most of the vibration and then try to install hardware that can live with the vibration you have left. Recording vibration makes sense only after good maintenance practices are in force. Good maintenance practices include:

  • Eliminate pipe strain
  • Align the pump and driver at operating temperature.
  • Dynamically balance the rotating assembly.
  • Keep the open impeller adjusted or the closed impeller wear ring clearances within manufacturers limits.
  • Insure that all mechanical seal environmental controls are functioning properly.
  • Check that the bearing has the correct amount of lubrication, no more or less.
  • And a hundred other things you know all about, and nobody does. In many plants preventative maintenance means “change the oil”.

See Vibration, V016

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Posted

  • On February 17, 2018