The Effects of Radial Thrust on Centrifugal Pumps

We are often asked about the reason why centrifugal pumps fail. Some say bearing or seal issues. Perhaps a broken shaft. However, in our experience, the common denominator in most centrifugal pump failures comes down to radial thrust in excess. As a result, below we will further discuss the effects of radial thrust on centrifugal pumps.

What is Radial Thrust?

Also known as axial thrust, radial thrust can be described as the pressure distributions on two sides of an impeller inside a pump that are not equal. This difference in the magnitude and direction of the flow velocity at the impeller’s inlet and outlet leads to a difference in momentum. It leads to a constant acting force on the impeller, in the direction of the pump axis. The radial force in the impeller can be steady or unsteady, either of which can be hazardous depending on the pump itself.

How Do I Know if My Centrifugal Pump Has Radial Thrust?

The effects of radial thrust in most centrifugal pump failures can be boiled down to this: excessive force leading to shaft deflection. It is usually the result of pump operation outside of the acceptable parameters or allowable operating region. It leads to unbalanced suction loads on the impeller, rotor imbalance, mismatched profiles, and improper clearances. Of course, other symptoms can develop as well as the result of radial thrust.

How to Identify Radial Thrust on Centrifugal Pumps

Any number of tests can be run to identify the condition if you suspect radial thrust. We recommend beginning by checking for shaft deflection, as that is a common sign of it. Look for shaft material fatigue, quick and ring seal failures, reduction in bearing life, and worn out bushings. You may also pump a high specific gravity fluid to see if it has a substantial effect on the radial load. However, we recommend performing the above with the help of a professional.

How to Prevent Radial Thrust on Centrifugal Pumps

All pumps and operations differ but you may try a combination of:

• Operating pump at normal parameters.
• Adding a bypass line from dischage header to the suction pipe.
• Using shaft material with high fatigue and endurance limit.
• Avoiding threads in the shaft’s middle portion.
• Placing proper distance between the impeller and casing.

Houston Dynamic Supply Centrifugal Pump Testing and Repair

HDS has over 30 years of experience working with centrifugal pumps in many industrial applications. We have one of the largest testing, repair, and rebuild shops in the entire Gulf Coast area. We can perform visual inspection, non-destructive testing, disassembly, and more for your centrifugal pumps and other rotating equipment. Contact us today to learn more.