Shaft Centering

The USP definition for stirring is that the shaft should be within ±2mm of the centre. This parameter is fairly easy to measure in open-design dissolution baths but is difficult to measure in the ‘clam shutting’ designs as there is not easy access (this also applies to the other hardware parameters). Shaft centering is dependent on two parameters — the position of the spindle (this is factory-set) and the position of the vessels. If the vessels are not set correctly or are loose then there is a possibility that the centering will be incorrect. Typically a 2mm off-centre shaft can add about 10% to a dissolution.