There are three areas of the swirl that will show the first visible signs of wear: the narrow “extended part” that forms one side of the inlet, the corner between the bottom and wall of the chamber and the bottom of the chamber itself. Of these three areas, the one that will have the most effect on the spray pattern will be the extended part. Once the extended part shows significant signs of wear, the swirl should be replaced.
In most cases, the orifice will wear uniformly and the hole diameter will grow in size, causing the flow rate to increase. RACA recommends to change the orifice discs when the flow rate increases by 5%, which is equivalent to a hole diameter increase of 2.5%.