Discussion on the causes of pump vibration

Thread Content

This text is excerpted from a report written by Steve Wilson for Grundfos; as the original text is quite long and its wording is rather obscure, only an excerpt is provided here. Regarding vibration testing, the Water Resources Association has published a complete set of standards adopted by the American **Standard Association (ANSI), which cover vibration dynamics, measurement standards, and allowable limits. The standard is ANSI/HI 9.6.4. I didn’t see this HI standard. But API 610 does contain relevant information (I just checked, and it’s available in at least version 11), so it should not differ much. The causes of vibration can be divided into three main categories: 1. Vibration caused by misuse, design, or manufacturing issues; 2. Vibration resulting from internal factors; 3. Vibration caused by external factors. The first category of causes is related to design and manufacturing problems, and unless you choose a low-quality manufacturer, the likelihood of this occurring is very low. So, it’s not discussed here. The focus is still on the latter two reasons. Internal reasons: These include:  Misalignment of the pump and motor—this is undoubtedly the most common cause of vibration in pumps.  Improper rotation – although the pump will still rotate if the direction is incorrect, the flow rate and the speed of rotation will decrease, and vibrations may occur due to fluid dynamics. Rotation should be checked and corrected.  Crankshaft – The crankshaft may be affected by certain site-related issues that can cause vibration.  Bearing wear/failure – Insufficient or improper lubrication can accelerate bearing wear and cause vibration. But even under \"intact\" conditions, bearings will wear out and fail due to fatigue. Inspecting the bearings, as well as the wear patterns and any \"flaking\" within the raceways, will help determine whether external forces are accelerating wear and causing vibrations.  Clogging – Excessive vibration does not always occur when a pump gets clogged, but it happens quite frequently. Vibrations caused by external factors: Experience shows that problems resulting from external factors are the cause of the vast majority of vibrations.  Pipe strain (misalignment between the pump and the pipe) – Pipe strain is the primary cause of pump vibration, and it should be considered first when investigating the reasons for pump vibration.  Weak foundation or poor anchoring – If the pump’s foundation is uneven or if the base plate is not properly secured or grouted, vibrations are likely to occur (just as in the case of a \"soft foot\"). In addition, the pump’s anchor bolts should be tightened once a year.  System resonance – Since every system has certain resonance frequencies, the \"acceptable vibrations\" within the pump can cause the system’s frequency to vibrate, amplifying those resonance frequencies and thereby increasing the vibrations inside the pump. This may cause the components to fail. Similar to the critical speed, adjusting the pipeline can resolve this issue.