Pump Coupling Selection

Selecting the proper coupling is critical for the efficient, long-term functioning of a pump and reducing maintenance downtime As it’s that time of year again and the Pump Centre Conference is now upon us, as a manufacturer of flexible couplings we thought it only ‘fitting’ to take a look beyond power and speed at some of the other key variables in the pump coupling selection process. Although the process can be time-consuming and even sometimes confusing, selecting the proper coupling is critical for the efficient, long-term functioning of a pump and reducing maintenance downtime. First off, the application of the pump must be taken into consideration as different applications can drastically affect both the size and type of coupling required. Secondly, since all pump couplings require maintenance and eventually replacement, the pumps maintenance requirements must be considered as well. The maintenance constraints of the entire plant must be carefully investigated to avoid selecting a coupling that works against the plant and its operations. While flexible couplings are a natural choice for pumps, it is not guaranteed that the same pump and coupling combination will be appropriate for every plant. With that in mind, the following criteria are of particular importance in the jaw-type pump coupling selection process: • Flexible-Element Replacement: Although all flexible-element couplings will eventually require replacement, not all replacements scenarios are equal. Sometimes it’s as simple as replacing the flexible element itself, but other times the entire coupling must be replaced. Depending on the initial design chosen, for instance for a jaw-type coupling, this could mean simply moving the couplings hubs back along the shaft and slipping the flexible element out via a sufficient distance between shaft ends (DBSE). In other cases, where the DBSE is not large enough, moving the pump or motor may be required. This second scenario will also require realignment of pump and motor and be much more time consuming and costly. Fortunately, there are split hub designs or couplings with wrapping external element which avoid the need to move the large components and their subsequent realignment. However, even these designs will, in a first instance, still require larger elements to be moved when swapping out an existing standard design coupling for a more maintenance friendly one. • Environmental Concerns: When selecting the proper coupling it’s also important to fully understand the productivity needs and environmental conditions of the plant. For instance, the failure of a coupling on a pump involved with critical industrial applications, such as drying or metallurgical processes will be more costly than that of an municipal pool pump, which means an easily maintained coupling that requires less downtime is critical. The material of the flexible element itself is also worth noting since environmental conditions and subsequent misalignment can drastically affect an element’s lifespan. For instance, elastomer elements can be damaged by prolonged exposure to sunlight or exposure to corrosive mediums. • Coupling Reaction Forces: Depending on the coupling type, misalignment can cause significant coupling reaction forces. Misalignment between shafts with stiffer couplings, for instance, imposes a greater force on the pump and motor bearings, which can shorten the lifespan of both. Coupling reaction forces are particularly important for pumps with lightweight motors since the forces enacted by the couplings can be greater than the rotor’s weight. Misalignment in this type of situation can lead to instability and vibration in the bearings. Selecting the couplings for pump applications requires careful consideration due to the various ways pumps can load couplings and the maintenance restrictions of different processes. When in doubt, it is best to consult a professional, and of course, if you have any questions KTR is always here to help.

For more information on Pump Coupling Selection talk to KTR U.K. Ltd