# Misconceptions in Overhauling Mechanical Seals for Pumps 1.

1.The greater the spring compression, the better the sealing performance. This is not the case. Excessive spring compression will cause rapid wear of the friction pair and instant burn-out. Over-compression deprives the spring of its capacity to adjust the end face of the rotating ring, resulting in seal failure.

2.The tighter the rotating ring gasket, the better. An over-tight rotating ring gasket brings more harm than benefit. First, it accelerates wear between the gasket and shaft sleeve and triggers premature leakage. Second, it increases the axial resistance for adjustment and movement of the rotating ring, making timely adjustment impossible under frequently changing working conditions. Third, the spring is prone to damage from excessive fatigue. Fourth, it deforms the rotating ring gasket and weakens the sealing effect.

3.The tighter the stationary ring gasket, the better. The stationary ring gasket stays basically static. Moderate tightness can improve sealing, yet over-tightening is harmful. Firstly, it causes excessive deformation of the stationary ring seal and impairs sealing performance. Secondly, stationary rings are mostly made of brittle graphite; excessive force can easily lead to cracking. Thirdly, installation and disassembly become difficult, and the stationary ring is easily damaged.

4.The tighter the impeller lock nut, the better. Leakage between the shaft sleeve and shaft (shaft leakage) is a common type of mechanical seal failure. It is commonly believed that shaft leakage arises from insufficient tightening of the impeller lock nut. In fact, shaft leakage has many root causes: failed or misaligned shaft gaskets, impurities between mating surfaces, large form and position errors at the shaft-sleeve fit, damaged contact surfaces, gaps between shaft components, overlong threads on the shaft end, etc. Over-tightening the lock nut only causes premature failure of the shaft gasket. On the contrary, proper tightening keeps the shaft gasket with stable compression elasticity. During operation, the lock nut will self-tighten appropriately to maintain good sealing between the shaft and sleeve.

5.New seals are always superior to old ones. Relatively speaking, new mechanical seals usually perform better than used ones. However, poor quality, improper material selection or large fitting dimensional errors of new seals will impair sealing performance. For polymeric and permeable media, it is better not to replace the stationary ring if it has no excessive wear. After long-term static service inside the stationary ring seat, polymers and impurities deposit and form an integrated layer, delivering favorable sealing performance.

6.Disassembly and overhaul are always better than no maintenance. Many technicians rush to disassemble and repair once mechanical seal leakage occurs. Sometimes the seal itself remains intact; leakage can be eliminated simply by adjusting working conditions or fine-tuning the seal. This method avoids waste, verifies fault diagnosis ability, accumulates maintenance experience and improves overhaul quality.