6.6 Shaft coupling selection

Shaft coupling selection

Shaft coupling selection is basically based on what type of engagement needed, torque, ambient conditions, speed, maintenance and cost. Generally speaking the cost per kW of a coupling is only a fraction that of a pump or motor (a pump usually costing at least 40 times that of a coupling and a 4-pole electric motor at least 20 times). The cost normally varies according to the size rather than the type or manufacturer.

A good way to compare the cost of couplings is to set the price in relation to the torque and range of shaft journal sizes to which the coupling can be fitted. The same pump shaft can, for example, be used for a torque range of 1:20 which occasionally means that the shaft dimension and not the torque is used when choosing dimensions of a coupling.

Furthermore, the motor shaft is often larger than the corresponding pump shaft. The motor shaft is dimensioned for torsional stress to a greater degree than the pump shaft, a motor is often used for belt drive, for example. This can also contribute to the necessity of using a larger size coupling.

Factors influencing choice of coupling, checklist

It is important, not least of all from a cost point of view, to establish a viable internal standard (if one does not already exist) by means of which a small number of type variations can cover the majority of coupling requirements within a company or plant. If no such standard exists, or if a new standard is to be developed, there is perhaps reason to modify the existing standard, the factors reviewed in the checklist, figure 6.6a should be considered.

Figure 6.6a Checklist for shaft coupling selection