We spoke with Bobby Watkins of Ruland manufacturing to get an overview of some basic coupling installation best practices. Ultimately, even if a coupling is properly selected, poor installation can cause failures.
“Always be sure your selected coupling is used within its ratings. We estimate here at Ruland that less than 25% of the couplings are installed by the book, if you will. Fortunately, most applications aren’t critical enough, and they were installed close enough, that most people don’t have problems. By the book installations… we think they are probably around 25%.”
It may seem common knowledge, but using the correct tool for the job is critical. One common tool required for installation is a torque wrench. Tightening the clamp screws on a motion-controlled coupling to the proper torque is critical.
“We have so many customers who don’t use a torque wrench; they throw a wrench on there and they tighten it to what they think is correct. Please use the torque wrench. It will save a lot of time, trouble, and coupling failure because you can definitely get coupling failures if the bolts are not torqued to the proper torque level. Shim stock, feeler gauges, or shaft alignment measurement tools such as dial indicator or laser system are also going to be of great help to you.”
There are certain best practices for different types of couplings. Rigid couplings, for example, should be installed starting with the inside two screws or four screws depending on the style of coupling. In the first pass, only seat to half of the recommended torque to ensure even clamping forces are maintained. On a rigid coupling, the sequence that you tighten the screws, inside to outside is important for proper installation with the shaft through the full bore of the coupling.
Beam couplings require other considerations. Tighten one hub first and, before tightening the second screw on the other side, rotate the coupling by hand to allow it to reach its free length. Beam couplings, in particular, are sensitive to being installed at the free length or proper length. If you install beam couplings either compressed or extended, the life of the coupling will be drastically reduced. This is a particular issue with beam couplings.
Lastly, there are Oldham couplings. When installing this type of coupling slide the hubs onto the shaft with the tenons at 90° before you insert the center disk, don’t tighten.
“Place the disk on one hub and center by hand. Use a shim the thickness of the coupling’s axial misalignment rating. Just to put this in a nutshell, Oldham couplings use a disk in the middle, and the disk actually moves up and down to accommodate parallel misalignment. A lot of installers, they think it’s the right thing to do. They’ll put together an Oldham coupling, they’ll squeeze the hubs together and tighten it down.What they’ve done is trapped that Oldham disk, and it’s preventing it from moving up and down to accommodate misalignment. If you don’t leave clearance, you’re going to have very limited life on the disk and you’re going to get all kinds of vibration problems as the disk is fighting to move up and down to accommodate the misalignment. It’s important to leave that gap by measuring with a shim when you install your Oldham couplings,” says Watkins.