Category Archives: Vertical Pump Shaft Bushing

Comparing Pump Component Composite Materials

There is one material property that can tell you a lot about how a composite material is likely to perform in a pump: The coefficient of thermal expansion (CTE). If the value is too high, the material can deliver inconsistent results in challenging services.

Why CTE?
A low CTE is essential for reliable performance because components like wear ringsthrottle bushings, and vertical pump shaft bearings run with tight clearances. A low CTE allows the material to experience normal frictional heat generation during contacting conditions without significant deformation.

Conversely, it is difficult for a material with a high CTE to maintain a tight clearance. When exposed to normal frictional heat generation or higher temperatures, a high CTE can quickly cause the component to “grow” and close the clearance. When this happens, contact increases, frictional heat generation increases, and premature failure of the component can follow. This is likely what happened to the bushing in figure 1:

Failed vertical pump shaft bushing made from high CTE material

Figure 1: Failed vertical pump shaft bushing made from high CTE material

The difficulty from the user’s perspective is everyone selling materials for pumps claims that their material has a “low CTE.” What this often means is “low CTE relative to other plastics.”
How do you define low CTE?

At Boulden, we define “low CTE” to mean “equal to or lower than the CTE of the metal parts in the pump.” Common metals used to manufacture pumps are carbon steel, 400-series stainless, or 300-series stainless, so we want to be close to or below the CTE for these materials.

Boulden B-Series
Because we think CTE is so important, we developed our B-Series materials with this in mind. If you are currently using PEEK-based components, contact Boulden about upgrading to our B-Series materials. B-835 is our replacement for 30% carbon fiber filled PEEK; B-1050 is our replacement for “abrasive resistant” PEEK blends. B-920 is a non-PEEK proprietary blend, also for potentially dirty services.

CTE of composite materials

Material CTE (in/in/F) CTE (mm/mm/C)
Vespel CR-6100 3.1 5.6
B-920 3.5 6.3
B-1050 5.1 9.2
410 SS 5.5 9.9
Carbon Steel 6.0 10.8
B-835 8.7 15.7
316 SS 8.9 16
30% CF Filled PEEK 15 27



A low CTE is critically important to the performance of a composite wear part in a pump and one of the reasons Vespel® CR-6100 has proven so reliable over the past 20 years. Boulden-supplied materials also offer ease of machining, simple installation practices, and material availability. Boulden keeps the material you need in stock and can supply raw material or machined parts including our patented PERF-Seal® with rapid delivery.

If you want to make your pumps more reliable, easier to operate, safer, and more efficient, contact Boulden today. We can help you choose the best material for your application and provide detailed design assistance.