6 Key Factors for Selecting the Right Coupling in Power Transmission

Couplings are used in virtually every piece of power transmission equipment. Connecting motor and gearbox/reducer shafts to conveyors, pumps, compressors, and other machinery transmit torque while absorbing vibration and facilitating disassembly and maintenance.

The Importance of Coupling Selection

Whether designing new machinery or performing maintenance on something that’s seen years of service, it’s vital to use the proper coupling. But, unfortunately, choosing the cheapest or the best delivery is a recipe for performance problems and premature failure.

What’s more, when replacing a failing coupling, recognize that the OEM may not have specified one of the best quality. A coupling more appropriate to your application may last longer and lower your maintenance costs.

So with that background, let’s look at what your coupling supplier needs to know so they can recommend the most suitable product.

1. Torque and Speed

Handling these is the primary role of the coupling. Your coupling supplier needs to know both. Note that couplings are designed with an overload capability, typically 200% of the catalog torque limit, to accommodate start-up loads.

2. Service Factors

Where will the coupling be installed, and what conditions will it see? For example, if it’s going outdoors, exposure to UV, ozone, low temperatures, and moisture likely take elastomeric couplings out of contention. Ask for couplings proven in your application and take manufacturer recommendations into account.

3. Space Available

The two factors are the gap between the shafts and the clearance around them. Some couplings, especially elastomeric units for high power and torque applications, have large outside diameters, so identify any restrictions.

When considering space constraints, you may encounter “torque density” or “power density.” This is the rated torque divided by the OD. Gear couplings have some of the highest torque density numbers.

4. Precision Required

In the context of couplings, this refers to:

• Tolerance for angular and offset misalignment (you may need to trade one for the other)
• Backlash (a key consideration in precision motion control)
• Windup (technically, torsional deflection)

For each of these, determine the limit of what’s acceptable and communicate it to your supplier.

5. Accessibility and Maintainability Considerations

If access to the coupling is difficult, it’s essential to select for long life, low maintenance requirements, and ease of repair/replacement. For example, avoid couplings that need lubrication (like gear couplings) and consider repairable ones by replacing only the flexible elements. (Grid coupling elements are often the least expensive.)

6. The Vendor

Find a vendor that works with a long list of coupling manufacturers and understands what your application needs. Ask about availability, stocking policies, and delivery: when a coupling does go bad, you want to know you can get a replacement quickly! Consider price only once you have candidates that will meet the performance requirements.

Get the Right Coupling for the Job

Shaft couplings may appear inconsequential, but that’s only until they fail. When choosing new or replacement couplings, consider all aspects of the application and share these with your vendor. Kor-Pak works with leading coupling manufacturers and can advise on what you should use. Contact us to get started.