Shaft Deflection – the Negative Effect on Seals, Bearings, Rings and Pump Life!
  • simsite

  • August 10, 2023

Many of our Customers have come to us and asked us to resolve an issue with their Mechanical Seals and Bearings failing prematurely in their centrifugal pumps. They believed that if they changed the manufacture, or type, of seal, or bearing, this will solve their problem.

Changing the mechanical seal, or bearings will NOT solve the problem! The reality is that these Customers do not have a “Seal Problem,” or a “Bearing Problem;” rather, they have a “Hydraulics Problem.” This Hydraulics Problem is causing excessive movement from shaft deflection and this excessive movement is causing the seals and bearings to fail prematurely! Therefore, they must solve the hydraulics problem in order to solve the seal and bearing problem!

The Solution is Simple:

1) Upgrade the cast metallic centrifugal pump impellers to SIMSITE® Engineered, 100% Machined, Structural Composite Impellers & Casing Rings.


a) Simsite® Impellers & Rings are 85% less weight, which means that shaft deflection is substantially reduced! How long would a pump last if it had no impellers? The answer is indefinitely, because there would be no shaft deflection, redial loading, or wear. SIMSITE® Impellers are as close to that situation as possible! That is why pumps which have been upgraded to Simsite® Impellers and Casing Rings last so long!

b) Simsite® Impellers & Rings are NOT “Cast,” or “Molded”; rather, they are “Machined” on 5 to 8 axis machining centers from one center position. If impellers are 100% machined from a solid block of material from one center position, there is no imbalance, not “mechanically”, or “hydraulically.” (All the vanes are within .001″ from each other). SIMSITE® Impellers are machined from a solid block of the patented Simsite® Structural Compo site which not only enables them to be perfectly balanced, but they do not corrode in seawater, river water, waste water, chlorine, or bromine!

c) Simsite® Impellers are engineered, designed, and machined so that the Customer’s “Operating Point” is the “Best Efficiency point;” which is extremely important because it not only makes the pump much more efficient, but it also reduces, or eliminates, radial loading and Shaft Deflection!

2) Upgrade the guide bearings and bushings to SIMSITE® Structural Composite bearings and bushings, which hold the Shaft more securely than bronze, rubber, elastomer, or thermoplastic bushings, and eliminates “cold flowing” from PTFE & other Thermoplastic Bearings! “Cold Flow is the distortion of a solid under sustained pressure with an accompanying inability to return to its original dimensions when the pressure is removed, or changed.”

3) Install SIMSITE® Stabilizing Bushings behind every seal and mechanical seal, which holds the shaft much more securely, reduces shaft deflection, breaks down the pressure in the seal chamber, and enables the Mechanical Seal, Guide Bearings, Radial and Thrust Bearings, Rings, Sleeves, and Motor to last much longer!

By John A. Kozel, the President of Sims Pump Company, Inc.


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