How to Optimize Coupling Performance – Part II

This is the second post of a two-part tip series that dives into couplings, how they work, and how to optimize their performance through best-in-class lubrication.

Our first post covered the basics – what are couplings, the two most common types of couplings (gear and grid couplings), and common operating challenges. This tip will focus on lubrication best practices.

Coupling lubrication

In couplings that require lubrication, it is critical that the proper lubricant be selected, applied correctly, and reapplied at the proper frequency. It is also important that the coupling be in good working order, in particular have functional o-ring seals and mating gaskets to prevent lubricant leakage.

Oil is, without a doubt, the best coupling lubricant, as it allows free and complete coverage and there is no thickener to separate or dry out (like you would have in a grease). Mobil products that have performed well in couplings include Mobil SHC Gear SHC 22M and 46M. These are high viscosity oils, made from PAO (polyalphaolefin) base stocks that contain extreme pressure additives to protect against sliding wear. They are also not susceptible to the centrifugal separation forces created during coupling rotation.

If you decide to use a grease for coupling lubrication, you should select a grease based on American Gear Manufacturing Association specifications CG-1, CG-2, and CG-3. The differences between the three ratings includes rotational speed, misalignment allowed, surface temperature and re-greasing interval.

Maintenance best practices

If you use a grease, the product’s performance is only as good as the greasing procedures used. First and foremost, if the coupling leaks and flings out the lubricant, the coupling will have a short life. Make sure o-rings and seals are in place and have integrity. Alignment is also key. The coupling must be aligned. If it isn’t, sliding wear will occur and shorten the life of the coupling.

Here are a few other important practices:

  • As part of the installation procedure, pack the coupling manually and by hand.
  • Repack the coupling by hand annually.
  • Between hand packs, re-greasing with a grease gun is acceptable.
  • When re-greasing with a hand gun, make sure the zerk fittings are below the 3 and 9 o’clock positions to ensure even filling of the coupling.
  • Only fill the cavity to 75% of capacity to allow for expansion.
  • Do both sides of the coupling.
  • A grease gun can develop 10,000 PSI, so make sure to pump the gun with a steady hand so as to not rupture the o-rings on the mating shafts.
  • Mobil recommends greasing coupling based on operating time and temperature, specifically:
    • 65°C / 8,000 hours or 1 year
    • 90°C / 4,000 hours or 6 months
    • 120°C / 1,500 hours or 2 months
    • 150°C / 200 hours or 7 days
  • Finally, coupling internals should be inspected annually by removing the coupling covers and examining the internal components. This is true even for couplings in intermittent service.

Hopefully this two-part tip series was helpful. If you have any further questions or comments, leave us a comment in the section below.