787. One of the many troubles occurring with centrifugal pump shaft packing is the excessive wear on the rings nearest the packing gland, while the rings nearest the impeller remain in good condition. This wear may be caused by __________.

Excessive wear on packing rings nearest the gland, while those near the impeller remain in good condition, is caused by improper adjustment of the gland nuts, which over-compresses the rings closest to the gland, leading to rapid wear due to increased friction.