Does a flexible coupling transmit no force when shafts are misaligned?

The short answer

No. Flexibility means a coupling can deform; that deformation can produce restoring forces and moments. A coupling that tolerates misalignment may still load neighboring bearings. Wind-generator support review should include those reactions where the selected coupling’s characteristics make them relevant.

Distinguish movement allowance from zero force

A spring can move while exerting force, and a flexible coupling can behave similarly in several directions. Its permitted displacement describes an operating boundary, not an assertion that the displacement is mechanically invisible. The relationship may be nonlinear and depend on design, load and temperature. A maximum angular allowance does not by itself provide the restoring moment at a smaller angle.

Trace the reaction into each machine

A coupling force applied beyond a bearing can create an additional bending moment because of its overhang. Axial restoring force can also interact with the locating arrangement. The same coupling displacement can therefore have different consequences with different bearing spacing or shaft-end geometry. A bearing load model that includes transmitted torque but omits relevant coupling reactions may not represent the complete installed mechanical interface.

Request the reaction data that the model needs

Ask the coupling supplier for force/displacement and moment/angle characteristics appropriate to the actual operating state, or its approved simplified method. Have the equipment designer include those reactions in the shaft-support review. KTR displacement limits establish that accommodation is conditional, not that MARSTON uses a particular coupling. Do not accept the phrase “absorbs all misalignment” as a zero-load assumption. Confirm both that the coupling survives the displacement and that connected supports can carry its resulting reactions. If reaction-force data are unavailable, keep that model input unresolved rather than set it to zero. The supplier may provide an approved simplified allowance or a design-specific assessment for the actual displacement and duty.