Improve Your Wastewater Pump Reliability

Better shaft bearing materials lead to longer life


Vertically suspended pumps with separate discharge (API Type VS4, shown in Figure 1) are generally used for sump pumps or waste water pumps. These pumps are a frequent source of headaches. The shaft bushings wear out leading to chronic repairs. Even though these pumps are in a “utility” service, this is one of the most challenging services for vertical pump shaft bearing material.There are a few different reasons the shaft bearings on these pumps fail, depending on the process conditions. These pumps can be installed in a wide range of conditions, so we should start by defining the service.

Define the Service

The first step is to clarify “sump pump” or “wastewater pump”, which are generic terms encompassing a wide range of services which tend to use the VS4 pump type. Some services are pumping primarily chemicals or chemicals mixed with water, and some of them are pumping primarily water mixed with dirt. Some services are very dirty, others are quite clean. Another variable is that the shaft bearings are flushed with different arrangements. Some of them are flushed with the process fluid, others with clean water, and others are greased.diagram of a typical waste water pumpFigure 1: Typical waste water pump configurationGiven the range of service conditions, there are several different problems which can cause the shaft bearings to fail. However, there are some commonalities. First, by design, the shaft bearings are along the column of the pump with a separate discharge for the process fluid. The bearings can run dry at start-up until the flushing fluid arrives. Sometimes, the external water flush is turned off; sometimes the flush lines from the process fluid are plugged; sometimes the grease supply is inadequate. In a chemical sump, the mix of chemicals can cause corrosion with metal wear parts. In very dirty sumps where the bearings are flushed with the process fluid, abrasive wear tends to be the main problem.Based on your conditions, frequency of failures, and damage witnessed, we should be able to help identify the main issues in your service and help you dramatically improve pump reliability. We have helped plants extend the life of these pumps from a few months to several years.

The Road Map

Sump Type Clean water flush Greased Bearings Product Flush
Process chemical sump
Water/dirt/chemicals       *
*In applications with a dirty water flush, a hard-coated sleeve under the shaft bearings is recommended.Considering the above, we have created the following table to help you identify the type of service where your wastewater/sump pump is operating.


If you have waste water/ sump pumps failing at your plant, use the table above to identify your service type and contact Boulden today. We have bearing materials for these pumps which can run dry, resist abrasion, run with marginal lubrication, and resist all of the chemicals likely to be encountered. We have material in stock available for shipment almost anywhere in the world and we can help you with design and machining of the parts. Until next time, be safe and healthy.Helpful Links:Boulden B-Series MaterialsBoulden Installation Guide for Vespel® CR-6100Amine Stripping Pump Case Study

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