Vibration – It’s not always Cavitation Excessive vibration is a sure-sign indicator that something is wrong with your pump. Find out how to identify if the vibrations are due to cavitation or indicate other troubles with the pump system. Vibration is a common occurrence in all pumps. However, it becomes a problem when it goes beyond normal levels. A common question raised by pump owners is, “Why is my pump vibrating so much? Is it because of cavitation, or is it something else? How do I correct it?” There are many reasons for vibrational troubles – you must identify the underlying problem so that you can correct it. Before we look at the potential causes of excessive vibration problems, let’s understand why vibration occurs.
Why do excessive vibrations occur in pumps?
Vibration in all machinery – including pumps – arises when there is an interaction between the hydraulic or mechanical force and the associated hydraulic/structural resonance frequencies. Generally, vibration troubles arise in new installations due to improper installation i.e. misalignment of pump and motor coupling, tension of pipeline on pump’s suction/discharge nozzles, pump installed at lower head than rated etc. However, they may also occur on existing installations due to changes in the system like – the addition of a new variable speed drive, changes to the pump piping, etc.How do I know if the excessive vibration is because of cavitation?
Most pump engineers and operators are familiar with the term cavitation. However, it has come to become a catch-all phrase to denote all vibration-related issues occurring in a pump. Generally, pump operators assume a cavitation issue, if the following signs occur: The noise level emitting from the pump is high The vibration in the pump is erratic with plenty of noise However, there are several reasons for flow-related troubles and excessive vibration in a pump. Cavitation is not always the culprit. All these problems cause excessive vibration and reduce the efficiency of the pump.How to identify the root causes of vibration in a pump?
Let’s take a look at how to identify the reasons for excessive vibration and prevent it:The vibration is due to Cavitation, If:
The vibration is quite loud and feels like gravel being thrown around the insides of the pump. Cavitation occurs when “cavities – low pressure bubbles” form in the displaced liquid at the pump’s suction end. Cavitation can occur due to: Poor design of the pipes Clogged suction end Pump operating far too left to the pump curve – resulting from VFDs (Variable Frequency Drives)
When the low-pressure bubbles enter the pump’s impeller end, it breaks/implodes due to a pressure imbalance. The breaking bubbles rise to the surface of the impeller damaging the housing and impeller.
The vibration is due to Air Entrapment (or Aeration), If:
The vibration is not excessively loud. Air entrapment occurs in the pump when bubbles are created in the liquid before reaching the impeller. It occurs when, Defoaming agents are not used When the liquid falls inside an open tank system The liquid level is lower than the top of the inlet pipe The displaced liquid is near its boiling point
Air entrapment is not a severe issue like cavitation. However, it can certainly damage the impeller, if not rectified.