Couplings are generally designed to handles a specific range of separation between the two shaft ends, typically referred to as the "BSE" (Between Shaft Ends) measurement. "BSE" measurements for a specific coupling can usually be found within a given manufacturer's catalog (which we hope would be one of ours!)
To increase the flexibility of a coupling to handle larger BSE situations, spacers can be added to a coupling design. Furthermore, by leveraging a spacer design with flexing elements on each side of the spacer, a coupling can generally be expected to be able to handle more misalignment as that spacer component grows longer. As a third benefit, spacer designs can also be designed to be "drop-out" making for easier system maintenance and repair. Pictured at right are three diagrams of disc couplings found in Lovejoy's disc coupling product offering. The first, the SU Type, leverages a single disc pack and two hubs. There is a single flexing element, and the "BSE" range is fairly limited. The second, the SX Type, incorporates two flexing elements and a center spacer element. This spacer element can be extended or shortened based off of a users unique "BSE", while the hubs and disc packs can remain common to the SU Type design. The third coupling shown, the DI Type, allows for the entire disc pack spacer assembly (comprised of the spacer, 2 disc packs, and 2 guard rings) to be removed from a system without being required to remove the hubs or push back any other pieced of equipment.
Whether a coupling is a "spacer" or "non-spacer" design does not describe the type of flexing element being incorporated into the design. Elastomeric couplings (such as Lovejoy's L-line or S-Flex) and metallic couplings (such as gear, grid, and disc - shown above) are all offered as core "non-spacer" designs, but are also available in standard and custom spacer varieties.
While there are many benefits to spacer designs, they also do have several important detractors. First, you are adding material and complexity, so the cost of the coupling will generally be higher as the "BSE" requirement grows. Also, as the "BSE" requirement grows and material is added, weight is also generally added to a system. This overhung load can lead to increased load on the systems being coupled (potentially generating excessive loads on bearings, etc.). Where spacers become long and weight becomes an issue (i.e. - cooling towers), spacers traditionally made out of hollowed out steel can be replaced with carbon fiber or composite tube spacers, though this change will add further cost to the overall coupling solution.
Should you have any further questions on spacer or non-spacer couplings, or should you have an application you would like us to quote... please do not hesitate to contact Lovejoy's application engineers at 630-829-1515 from 7am to 5pm Central Standard Time. (For additional contacts, or more product information... please visit our corporate website.)
