Causes of Excessive Vibrations in Rotating Equipment
In rotating equipment, excessive vibrations can be a serious source of many problems both to-be and pre-existing. Finding the sources of excessive vibrations in machinery can sometimes be a challenge, though a necessary step to resolve current issues and prevent future downtimes for rotating equipment. This article explores three common causes of vibrations in rotating equipment, such as centrifugal pumps, in an effort to prevent further issues due to excessive vibrations. The three common causes are: misalignment, inadequate base/mounting of the equipment, and imbalances within the rotating equipment.
Misalignment is a common cause of problems in rotating equipment, from the couplings to the shaft to the impeller: misalignment can wreak havoc on a pump. “Pump shaft misalignment occurs when one shaft or surface is moved from its desired position. These movements can lead to misalignment in the entirety or partial sections of a pumping system.”1 The causes of misalignment vary, but it is recommended to first observe the connection between couplings on a pump with a dial or laser indicator, as misalignments can often be due to poor connection between couplings. Other causes of misalignment can arise due to thermal expansion, “Strain, attached piping runs can force equipment out of alignment– Torsional Movement, initial high torque caused during startup– Settling, base plate settles to lower position”2
Any item of industrial equipment which rests on an integral base will be compromised, at least to some degree, if the base itself is unbalanced or if the equipment is unbalanced upon the base. This can be a cause of excessive vibration in many cases, as it is not very difficult for this mistake to be made. “The improper mounting of the machine without holding it rigidly to the ground causes the machine to vibrate.”3 It is recommended to observe the base plate/foundation’s bolts to start to determine if the base plate/foundation is uneven. One of the best practices to identify an imbalance issue which may be causing excessive vibrations is to, once the equipment is first installed, keep a data chart of the pump’s vibrations in different axial locations at different points on the pump. By doing this, if excessive vibrations emerge later, one can again measure vibrations, compare to the original vibration data and determine in which direction(s) vibration is occurring excessively to find the source of the vibrations.
An imbalance in the rotating equipment is essentially what the issue of vibration is. The imbalances may lie in one or more areas of the equipment. “Vibration in rotating machinery is commonly caused by imbalance. Imbalance is a condition where a shaft’s rotational axis and weight distribution axis (mass of centerline) do not coincide due to uneven distribution of mass around a rotating shaft’s centerline.”4 There are a plethora of causes of balancing issues which result in excessive vibrations, but the solution as a whole is to properly inspect equipment before its installation, especially with regard to proper tolerances throughout the pump’s shaft and its impeller.
There is not a guaranteed method of preventing excessive vibrations within rotating equipment. However, rotating equipment should function at an optimum level as the manufacturer specifies as long as the rotating equipment is properly installed, maintained and repaired & rebuilt with the correct replacement parts. It is advised to conduct a thorough inspection on an item of rotating equipment, such as a centrifugal pump, whenever monitoring oil level or other brief, routine inspections. The ideal would be to monitor for excessive thermal release and vibrations whenever inspecting a pump (i.e. daily or weekly, etc.), although it is unlikely that this measure would be taken often due to the time needed to conduct a thorough analysis of the rotating equipment. Regardless, the best practice to avoid excessive vibrations from occurring post-installation is to monitor a pump and keep track of its data in regard to vibrations, as well as other areas such as heat being released, rate of oil loss and efficiency levels for the rotating equipment.
2 Same as 1
Laser vs Dial indicators: A guide to which one is better A good example of why you need aligned parts Alignment is a critical