A vibration often present in the reciprocating machinery, and also the rotary machinery, has its origins in small oscillations of angular velocity. The torsional movement appears superimposed on the continuous rotational movement of the rotating parts and it is the periodic oscillations around the rotational speed which are the origin of the torsional vibration.
Torsional vibrations can cause serious damage to equipment. Unfortunately, torsional vibration is not detected with conventional vibration measurements, so it is necessary to resort to specific techniques. This makes this kind of vibration doubly dangerous. Torsional vibration can cause catastrophic failure due to fatigue of the material, which may go unnoticed using the usual vibration measurement, without previously revealing itself as a problem of excessive vibration or any indication of anomaly in the machine.
Torsional vibration usually appears in gear trains, crankshafts or clutch systems.