What are the basics of coupling installation?

Installation overview: Even if a coupling is properly selected, poor installation can cause failures, staying within the recommended misalignment ratings of that coupling at installation is critical. Here, we will cover several coupling types and what to be careful of during installation. Always be sure coupling is used within the manufacturer’s ratings. Use a torque wrench for proper screw seating torque.

The first, and arguably most common tool for installation is the torque wrench. It’s important to use a torque wrench when your tightening screws on couplings. It’s an overlooked piece of information; over-torquing or under torquing the screws on a coupling is going to vastly affect how well they clamp and, ultimately, how long they last.

Next is the shim stock or feeler gauge and shaft alignment measurement tools such as a dial indicator system or laser alignment system. With rigid couplings, for example, be sure to install screws starting with the inside two or four depending on the style. When we have a 4 screw version, the way this coupling should be installed is the two inner screws should be tightened to 50% of the total torque. Then, go out to the outer screws, bring those up to 50% of the torque and go back and bring the two inside screws up to 100%. Lastly, go to the outside screws and bring them up to 100%. This tightening sequence is critical.

For beam couplings, tighten first and before tightening the second, rotate the coupling by hand to allow it to reach its free length. Certain couplings are prone to be installed either compressed or extended. Beam couplings and bellow couplings will have the biggest issue with this; it’s important not to install these couplings either compressed or extended. It drastically reduces the service life of a coupling if it’s not installed at the correct length.

When installing an Oldham coupling, slide hubs onto the shafts with tenons at 90° before inserting the center disc but do not tighten. Place one disc on one hub and center by hand, use a shim the thickness of the coupling’s axial misalignment rating and slide the second hub into the groove until the tenons touch the shim. Tighten both hubs and remove the shim.

Oldham couplings have a disc and that disc actually moves up and down. There needs to be a gap or space to allow the disc to move, if we were to assemble this and squeeze the hubs together and tighten the hubs down we have trapped the disc at that point. This is why we talk about shimming and leaving a gap between the face of the Oldham disc and the tenons on the coupling hub.

Disc or bellows couplings: It is critical that these type of couplings are not installed under compression, not extended either, but at the proper length. Tighten one hub first and before tightening the second one rotate the coupling by hand to allow it to reach its free length and then tighten the second hub.

Jaw couplings. For small sizes, slide hubs onto shafts with tenons facing each other. Fully tighten screws on one hub. Do not attempt to press standoffs into the balance holes. Insert jaws of the second hub into spider openings until standoffs contact the second hub. It may require some force to press the second hub into the spider, this is common.

Ruland
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