6 Common Mistakes with Flexible Couplings

Flexible shaft couplings are simple and relatively inexpensive devices that are not difficult to install or maintain, yet many fail prematurely. These failures also happen despite the devices being specially designed to tolerate slight misalignment and to cope with tough operating conditions including temperature extremes, humidity, loads and more. Here are six common mistakes made in assembly and maintenance of flexible couplings.

1. Misalignment—While couplings are designed to allow some misalignment and varying degrees of flex, excessive misalignment between joined shafts is one of the most common reasons for failure. Often, a mechanic will not check the alignment before installing a new coupling and assumes that if the coupling fits, the shafts must be aligned properly. Sometimes the mechanic does not even know that alignment is required. One of the telltale signs of coupling misalignment is the presence of dust under the part. Prevention tip: Make alignment a prerequisite prior to coupling installation. Laser alignment tools make the task easy, quick and accurate.
2. Not Following Manufacturer Installation Instructions—All too often, mechanics assemble couplings without referencing the manufacturer’s instructions and this can lead to premature failure. The old saying “more haste, less speed” is especially true when it comes to installing couplings, and technicians should be urged to refer to the specific manufacturer’s installation directions, adhere closely to them and not rush the process.
3. Incorrect Coupling Specifications—Not all flexible couplings are the same. There are many different types and for optimum power transmission. The right coupling must be selected. Unfortunately, this does not always happen, and the result is premature coupling failure. Prevention tip: Make sure there are appropriate couplings in the spares inventory and that the maintenance department is aware of the various design specifications. If the operation is experiencing frequent coupling failure despite the alignment being in order, it is recommended that engineers document the system conditions at failure so a more appropriate coupling can be used that is more suited to the machine’s load, torque, temperature, horsepower, etc.
4. Insufficient Lubrication—Always follow the manufacturer’s specifications about lubrication—both the frequency of lubrication and the type of lubricant required. Failure to adhere to these instructions will lead to problems. Prevention tip: Remember, the coupling and the bearings may not be able to use the same lubricant, so always check the instructions carefully.
5. Poor System Maintenance—Without proper maintenance, the efficiency and effectiveness of a system will be compromised. A coupling is just as important as a pump, gearbox, bearing assembly or any other component of precision machinery and must be given the appropriate level of care and maintenance. A regular maintenance schedule should include the following:
   • Clean and relubricate gaskets and sealing rings and replace if necessary.
   • Check alignment.
   • Remove hard grease.
   • Ensure shaft size is appropriate.
   • Replace worn or twisted elastomer.
   • Check for properly seated keys.
   • Check and tighten set screws and bolting in the right order and to the torque requirement.
6. Lack of Information—The more knowledge about why couplings fail, the fewer chances there are to experience issues relating to coupling failure in the workplace. The better informed the mechanics and maintenance team are about the importance of the correct specification, assembly and maintenance of couplings, the more reliable the machinery will be. This will lead to better equipment performance, enhanced productivity, less downtime and likely improved profitability.