5 Reasons Why Couplings Fail

A coupling connects two rotating shafts, allowing rotary motion and torque. Although couplings are relatively inexpensive and easy to maintain, their failure can cause major inconveniences and huge financial losses. There’s even a risk of injury. At Vissers, we believe prevention is better than cure, so look out for these warning signs that your couplings are about to fail:
” Undue noise or excessive vibrations and wobbling
” Seal or bearing failure, lubricant leakage or contamination
” Higher than normal power consumption

To prevent these warning signs of coupling failure in the first place, it’s important to know the top five reasons why couplings fail:

1. Misalignment
Misalignment can be caused by improper installation of the pump and motor, bent shafts or pipe strain. It’s important to know the misalignment conditions of the application when selecting the coupling – angular, parallel, axial or complex misalignment. Flexible couplings work best in these conditions. However even flexible couplings have their limitations, and underestimating the degree of misalignment can cause loads that surpass coupling specifications. This can cause excessive wear and premature failure of bearings. It’s also important to take dynamic load shifts and thermal growth into account. Laser alignment can help extend coupling life, while regular adjustments may be required to keep it aligned during operation.

2. Lack of Lubrication
Many couplings, like gear and grid couplings, require proper lubrication. Check the lubricant levels of these couplings twice a year and periodically flush to remove contaminants that may cause premature coupling failure.

3. Incorrect Selection
Price and delivery are often the primary selection factors for couplings, however selecting incorrect couplings can have dire consequences for coupling operation. Make sure you select your couplings in the early stages of the design process to ensure that the coupling chosen is the right one for the functions required. For example, fuse couplings don’t allow further energy transfer upon failure, while fail-safe couplings are designed to continue working even after failure.
When choosing couplings for an application, you must consider many factors such as misalignment, torque, windup, backlash, inertia, stiffness, shaft mounting, environmental factors, limitations on space, service and maintenance factors, and cost. This process of evaluation must be repeated any time conditions change throughout the application’s lifecycle. Other conditions to be aware of include dampening – it’s important to select a coupling with the correct amount of dampening (which minimizes shock and vibration to reduce stress on system components), application shaft speed (any degree of misalignment can affect safe operation speed of the couplings) and electrical isolation, as voltage differentials between shaft ends can lead to bearing and system wear.

4. Improper consideration of inertia, windup or backlash
Couplings need to be suited for their application. Inertia refers to a coupling’s resistance to changes in velocity and this determines whether the coupling can keep a constant speed in response to external forces (such as torque). Too much coupling inertia can degrade the performance of the entire system.
Present in all couplings, windup is known as torsional rigidity and is the rotational deflection between the driver and the load, much like winding up a spring. Windup needs to be considered to maintain accuracy of location, as it may lead to a difference in angular displacement from one end of the coupling to another.
Backlash is the momentary loss of motion in a coupling, which is experienced when the direction of torsion is changed – causing the coupling to bend and compress. Any amount of backlash can be detrimental to an application, causing lack of accuracy in positioning and making it difficult to tune the system.

5. Lack of regular maintenance:
Lack of regular maintenance can cause couplings to fail prematurely. Scheduled inspections should include regular visual inspection for signs of wear or fatigue, regular cleaning and lubrication and documented, dated maintenance checks.

If you want to make sure you’re choosing the right couplings for your application, please call our toll-free number 1-800- 367-4180. We have experts on hand to help you choose, install, and maintain a variety of equipment.