Nowadays, there are many classifications of centrifugal pumps in industry, with different classifications in different aspects. For example, based on the different mechanical seals of the impeller, we can divide it into single-stage pumps and multi-stage pumps. A single-stage pump refers to a pump shaft with only one impeller, while a multi-stage pump refers to a non-equilibrium mechanical seal with two or more impellers; During the work process, we can also classify centrifugal pumps into low-pressure pumps, medium pressure pumps, and high-pressure pumps based on the different pressures between water columns; According to the different suction methods of the impeller, we can also divide it into single-sided water inlet pumps and double-sided inlet pumps. Although there are many types of centrifugal pumps in industrial production, the primary factor causing leakage is the same. Nowadays, the primary factors causing equipment leakage include: firstly, improper selection of sealing materials, which greatly affects the working function of centrifugal pumps due to imported mechanical seals; Secondly, the internal components are severely worn out; Thirdly, the uneven cooperation between the dynamic and static rings is also the primary factor leading to leakage; Fourthly, the sealing between the stationary ring and the stationary ring seat is not tight. From this, it can be seen that the selection of materials, the impact of resistance, and the damage of parts are the primary factors causing mechanical leakage. We should start from these three aspects in order to effectively deal with sealing issues in industrial production.

Selection of mechanical sealing materials

When selecting mechanical seal materials, the characteristics of the material should be fully considered, such as acidity, alkalinity, corrosiveness, particle size, viscosity, temperature, pressure, etc. Based on these factors, suitable friction materials should be selected to reduce the friction coefficient and lower the possibility of end face thermal cracking. The material of the resistance pair should have excellent wear resistance, heat shock resistance, thermal conductivity, self-lubricating properties, high mechanical strength, and suitable hardness. Therefore, the suitable resistance pair material is the condition for the stable operation of the mechanical seal, followed by the construction method of the mechanical seal. Users can choose according to the sealing manual based on their practical application.

Analysis and differentiation of leaked elements

Leakage of mechanical seals during static state of equipment. After static testing, check the leakage amount. If the leakage amount is small, there are often doubts about the O-ring of the dynamic or static ring seal; When the leakage is large, it indicates that there are doubts about the collision between the dynamic and static rings. On the basis of checking the leakage amount and distinguishing the leakage location at the beginning, manually turn the disk to check. If there is no significant change in the leakage amount, there are questions about the dynamic and static ring seals; If there is a significant change in the amount of leakage, it can be distinguished as a conflicting issue; If the material is sprayed along the axial direction, it is mostly due to damage to the O-ring of the moving ring; If the material is sprayed radially, it is mostly due to the failure of the static ring sealing gasket.

Leakage occurs during testing. The centrifugal force generated by high-speed rotation during testing can restrain material leakage. Therefore, during testing, after the failure of the sealing between the cleaning shaft and the end cover, the foundation is damaged due to the collision between the dynamic and static rings. The primary factors that prevent secondary failure include: (1) abnormal conditions such as looseness, cavitation, and pressure buildup during start-up, resulting in significant axial forces that separate the dynamic and static rings; (2) When the mechanical seal of the equipment is tightened too much, it causes serious damage to the resisting pair and scratches. The O-ring of the moving ring is too tight, and the spring cannot adjust the axial floating amount of the moving ring; (4) There are particles in the working medium that enter the contact pair during operation. The selection of the contact pair end face friction (5) is incorrect, and the selection of the end face specific pressure and contact coefficient is improper, resulting in damage to the contact pair.

The natural leakage of the centrifugal pump's bottom chamber during normal operation is caused by changes in working conditions or improper operation. (1) The centrifugal pump has been idling for a long time, resulting in a secondary thermal cracking; (2) Cavitation or prolonged pressure build-up; (3) There are many granular substances or polymeric and adhesive substances mixed in the material liquid, and the mechanical seal itself is not suitable for this type of material. When the spring compression force is not strong, it may scratch the resistance pair; (4) Significant changes in medium temperature or drastic changes in environmental temperature can damage the machine seal.

Precautions during equipment and repair of mechanical seals

(1) The tightening amount of the dynamic ring spring is not necessarily better. An appropriate tightening amount is beneficial for the adjustment of the dynamic and static rings of the mechanical seal. If the tightening amount is too large, the possibility of overheating, wear, and scratches during operation will increase, directly affecting the service life of the mechanical seal. (2) The cooperation between the O-ring of the dynamic ring and the shaft is not necessarily better if it is tighter. If the cooperation between the O-ring of the dynamic ring and the shaft is too tight, it may prevent material leakage on the surface and affect the axial adjustment of the dynamic ring during operation, which may cause uneven cooperation of the end face and accelerate the wear of the O-ring.

Several misconceptions in repairing mechanical seals for pumps

(1) The greater the compression of the spring, the better the sealing effect. Otherwise, the original. The spring compression is too large. May cause rapid wear and tear on the resistance pair. Instantly burned, excessive compression caused the spring to lose its ability to regulate the end face of the moving ring. Causing seal failure. (2) The tighter the dynamic sealing ring, the better. The original dynamic ring seal is too tight, which is harmful and not beneficial. One is to intensify the wear of the sealing ring and shaft sleeve, leading to premature leakage; The second is to increase the axial adjustment of the dynamic ring. Resistance to movement. Unable to make timely adjustments when there are frequent changes in working conditions; The third is that excessive fatigue of the spring can easily damage it, and the fourth is that it can cause deformation of the dynamic ring seal. Affects the sealing effect.

Conclusion

It can be seen that in industrial production, the selection and repair of mechanical sealing equipment are very important. Therefore, when repairing mechanical seal equipment, we need to fully consider all aspects and elements of the mechanical seal equipment in order to fully protect it. However, China's technology in this area is still very advanced, and we will continue to explore and strive in our future internships.