Misunderstandings on Maintenance of Mechanical Seals for Pumps

1. The greater the spring compression, the better the sealing effect. In fact, it is not the case. Excessive spring compression can cause rapid wear and instant burning of the friction pair; excessive compression causes the spring to lose the ability to adjust the end face of the dynamic ring, resulting in seal failure.

2. The tighter the dynamic ring seal, the better. In fact, too tight a dynamic ring seal is harmful rather than beneficial. First, it aggravates the wear between the seal and the sleeve, causing premature leakage; second, it increases the resistance to axial adjustment and movement of the dynamic ring, and cannot be adjusted in time when the working conditions change frequently; third, the spring is easily damaged due to excessive fatigue; fourth, the dynamic ring seal is deformed, affecting the sealing effect.

3. The tighter the static ring seal, the better. The static ring seal is basically in a static state, and the sealing effect will be better if it is relatively tight, but over-tightening is also harmful. First, it causes excessive deformation of the static ring seal, affecting the sealing effect; second, the static ring material is mostly graphite, which is generally brittle, and excessive force can easily cause fragmentation; third, it is difficult to install and disassemble, and it is easy to damage the static ring.

4. The tighter the impeller lock nut, the better. Among mechanical seal leakage, leakage between the sleeve and the shaft (inter-shaft leakage) is relatively common. It is generally believed that inter-shaft leakage means that the impeller lock nut is not tightened. In fact, there are many factors that lead to inter-shaft leakage, such as failure of the inter-shaft gasket, offset, impurities in the shaft, large shape and position errors at the fit between the shaft and the sleeve, damage to the contact surface, gaps between the components on the shaft, and too long shaft head threads. Excessive tightening of the lock nut will only cause premature failure of the inter-shaft gasket. On the contrary, moderate tightening of the lock nut will keep the inter-shaft gasket always maintain a certain compression elasticity. During operation, the lock nut will automatically lock in time to keep the shaft in a good sealing state.

5. New is better than old. Relatively speaking, the effect of using a new mechanical seal is better than the old one, but if the quality or material of the new mechanical seal is not selected properly, the large error in the matching size will affect the sealing effect; in polymeric and permeable media, if the static ring is not excessively worn, it is better not to replace it. Because the static ring is in a static state in the static ring seat for a long time, the polymer and impurities are deposited as one, which plays a better sealing role.

6. It is better to dismantle and repair than not to dismantle. Once a mechanical seal leaks, people rush to repair it. In fact, sometimes the seal is not damaged and the leakage can be eliminated by adjusting the working conditions or adjusting the seal appropriately. This can not only avoid waste but also verify your own fault judgment ability, accumulate maintenance experience and improve maintenance quality.