Top Alignment Issues for Centrifugal Pumps
It's a commonly known fact that one third of all bearing failures and up to half of downtime costs are caused by the misalignment of rotating machinery. This can cause friction and vibration that wears bearings and eventually damages the pump.
In addition, couplings and shafts can deteriorate prematurely and seal lubricant may leak. What's more, pumps will use more power, and mounts or pump/motor casings can break over time. So, why does misalignment continue to be an issue experienced in many industrial plants? Let's outline the main causes of misalignment:
1. Shipping and handling
While the pump and motor set is usually delivered pre-aligned from the factory, issues can occur during the shipping and delivery process. It's critical to check that the pump and drive motor are correctly aligned before setting up and running your pump.
2. Incorrectly mounted base pump
The first and most obvious thing to check is whether the base plate is mounted correctly on a suitable foundation. Specifically, the foundation's surface should allow the base plate be mounted without distorting or becoming stressed.
3. Installation issues
Despite clear installation instructions and specified alignment, it's easy to misalign the motor shaft and pump shaft centerline at an angle (called angular misalignment). You can also misalign the centerline horizontally or vertically while shafts are parallel (called parallel misalignment).
4. Foot issues or soft foot
A condition known as "soft foot" is a common condition in rotating machinery. This occurs when rotating equipment is set in place on its base plate or frame, but one or more than one of the feet are not making sufficient contact at the foot points of the frame*. Soft foot is sometimes discernible when the machine rocks (called gross soft foot), but in many cases it's not detectable and can even lead to machine failure if not addressed.
Make sure you check that the base plate is mounted correctly and not distorted or damaged, that shims are correct and anchor bolts are tight. This is particularly important as the pump can appear normal when everything is shut down, but issues can develop during operation, such as motor torque and thermal stresses.
There are a number of ways to align your centrifugal pump. You might need to reposition the pump or motor to get align the centrelines of its shafts. It's often easier however, to make adjustments to the motor.
Loosen the motor anchor's bolts to shift it to one side (called horizontal adjustments) or add or remove shims under the motor's feet (called vertical adjustments). Alternatively, leveling screws can be adjusted.
Always remember that if either the pump or the motor have been moved or repositioned in any way, you must check the alignment before you run the machine.
For more strategies on ways to align your pump, read The 3 main alignment methods.
* John Piotrowski, The Shaft Alignment Handbook