Shaft coupling used with centrifugal pumps can be divided into rigid and flexible types. Rigid couplings are mainly used to connect shafts in perfect alignment. The smallest degree of misalignment will cause considerable stress on the coupling and to the shafts. The following types are used:
Split couplings (DIN 115)
Face plate couplings (DIN 758, DIN 759)
Flexible couplings to DIN 740 are elastic; slip free connecting elements between drive and driven machine which accommodate axial, radial and angular misalignment (Fig.1) and damp shock loads. The flexibility is usually achieved by the deformation of damping and rubber elastic spring elements whose life is governed to a large extent by the degree of misalignment.
Fig. 1 Misalignment
Fig.2 shows a spacer coupling between a pump and drive, its function is to permit removal of the pump rotating assembly without disturbing the casing or drive (back pull out design).
Fig.2 Pumps with spacer couplings