What’s the Point of Precision Shaft Alignment When We Use Flexible Couplings?

This is a common misconception in some industries surrounding flexible couplings. Some maintenance and production individuals believe that flexible couplings are designed to allow for a few degrees of misalignment.  This is not quite the case.  While flexible couplings do tolerate some amount of misalignment, this is not their intended purpose.  The greater the misalignment, the shorter the life expectancy of the coupling.

Flexible couplings are designed to reduce some of the resulting shock impact that occurs when rotating shafts are started up.  Another primary function is to act as a type of “fuse” between the motor and the driven machine.  In the event of an abrupt failure or overload on either the motor or the pump, the flexible coupling will be destroyed instead of possibly both machines.

2nd Coupling Photo a

Shaft misalignment is the primary contributing factor in over 50% of rotating equipment breakdowns.  A single coupling failure can cost thousands of dollars, just in lost productivity due to downtime.  The precision shaft alignment performed in the field needs to be better than what the couplings will tolerate. Machinery has the potential to change position overtime causing misalignment. This is the main justification for precision machine alignment.

Through the proper use of precision shaft alignment equipment, we can be certain that our rotating machinery shaft alignments are done to a far more precise degree then we could ever do it without these instruments.  The justification is the cost savings from greatly reduced equipment failures.

Save the Machine!

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  1. Dragan Stanovic on July 30, 2016 at 2:02 pm


    Recently our engine CAT 3408 were overhauled in workshop.They removed engine completely out
    and when installed back no alignment were done.After one week our flexible coupling Vulcan P7520
    found damage inner and outer ring.Rubber element still in good condition.
    What kind of alignment we have to do to avoid this kind of damage in future.

  2. Brad Case on August 22, 2016 at 3:13 pm

    Dragan, A precision shaft alignment needs to be done with either dial indicators or a laser shaft alignment. The goal of precision shaft alignment is the make the driver and driven machine’s rotational center lines collinear (within acceptable shaft alignment tolerances) AT operating temperatures.

    As your driver is a CAT 3408 engine, more than likely you will also need to compensate for thermal growth when performing the shaft alignment. Your equipment OEMs should be able to help you with the Thermal Growth Targets or you can use our free Therm Align App to calculate it.

    You can download the Therm Align App through Apple’s App Store or through Google Play.

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