In power transmission, a coupling is a device used to connect a driving machine, such as a motor, engine, or turbine, to a driven machine, such as a fan, pump, compressor, or other machine. There are numerous styles of couplings, each with specific design characteristics, that make them suitable for their respective applications.
All quality couplings are packaged with installation and maintenance instructions. Sadly, they are seldom read!
Photo courtesy of Lovejoy, Inc.
Installing a coupling by using the manufacturer’s instructions is pivotal to proper operation and maintenance. Below is a prime example of “not” reading a coupling manufacturer’s installation instructions.
Most coupling manufacturers state a maximum allowable misalignment value based on coupling size. It is important to note that in most cases, these values are the maximum misalignment the coupling can tolerate before the element fails.
Aligning “machines” to acceptable “coupling” misalignment values still generates forces across the coupling or point of power transmission from the driver to the driven machine. Precision shaft alignment is all about aligning the machines to reduce force on the bearings, seals, etc.
Coupling tolerances should not be considered the alignment tolerances for precision shaft machinery alignment. Unless otherwise specified, align to the tolerance of the alignment tool manufacturer.
By the way, those coupling installation instructions also state that the coupling will last longer (or perform better) if properly aligned.
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Long Live the Machine!