Effects of Misapplied Applications in Industrial Equipment

Let’s take a look at some of the effects of misapplied applications in an industrial equipment setting that often lead to pump repairs, or worse, a complete replacement of broken equipment.

 

SHAFT DEFLECTION


Shaft deflection occurs when a constant radial load in one direction causes the pump shaft to bend downward. When the shaft is rotated 180 degrees, the shaft continues to bend downward in a similar way.

 

 

It is critical to limit shaft deflection to avoid internal parts from rubbing together.
It is critical to limit shaft deflection to avoid internal parts from rubbing together.

 

Shaft Deflection is a function of four factors:

  1. Radial force in the impeller
  2. Length from impeller to radial bearing
  3. Shaft diameter (the smaller the diameter, the more deflection)
  4. Material properties (different materials have a different flex)

 

When in use, the shaft that is deflected rotates along its centerline — even though the centerline may not be straight. This in turn produces a “reversal of stresses” in the shaft (in each revolution) that can lead to cracking and eventually the breakage of the shaft.

 

It is critical to limit shaft deflection to avoid internal parts from rubbing together. If a shaft deflects too much, some of the rotating parts may be exposed to the stationary parts. And, if you happen to have stainless steel parts (which most pumps do), they will gall as soon as contact is made. Moreover, galling will almost always become progressively worse and if left untreated, can result in a complete seizure of the pumps rotating elements.

 

SHAFT WHIP

There is often confusion between shaft deflection and shaft whip. Unlike shaft deflection, which is affected by radial load, shaft whip results from rotor dynamic issues.

 

When shaft whip occurs, the shaft shifts 180 degrees from its centerline in every rotation creating a cone shape. This is usually caused by an unbalanced impeller on some side of the shaft because that’s where your highest velocity energy typically occurs.

 

When shaft whip occurs, the shaft shifts 180 degrees from its centerline in every rotation creating a cone shape.
When shaft whip occurs, the shaft shifts 180 degrees from its centerline in every rotation creating a cone shape.

 

SHAFT RUNOUT

Runout is defined as the degree to which a shaft deviates from true circular rotation. Every shaft has a center of rotation, or a centerline, and any stray from this centerline is considered runout. If runout is severe enough it can cause a number of problems with equipment including excessive vibration, seal wear or bearing damage.

 

Thankfully, it’s easy to check for runout before the alignment process begins using a dial indicator and magnetic base. Just zero the indicator on the outside diameter of the coupling hub and then slowly rotate the shaft, watch for runout and measure the amount. Next, move the indicator to the shaft adjoining the coupling hub and measure the same way. If the hub and shaft travel approximately the same amount, the runout is likely due to a bent shaft.

 

— It is possible to have all three events occurring simultaneously —


By educating our customers about the machinery they rely on for their day-to-day operations, C&B Equipment can help increase uptime, while decreasing the need for costly off-site repairs. That’s what we call Uptime Solutioneering™.

Check out our source, Empowering Pumps!

 


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