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Mechanical seal sealing surface to have a certain pressure, so as to play the role of sealing, which requires the mechanical seal spring to have a certain amount of compression to the sealing end of a thrust, rotating the sealing surface to produce the required ratio of sealing Pressure In order to ensure this one than the pressure, the mechanical seal requires the shaft can not have too much channeling amount, generally to ensure that within 0.5mm. However, in the actual design, due to unreasonable design, the pump shaft often produce a large amount of channeling, the use of mechanical seals is very unfavorable. This phenomenon often appears in the multistage centrifugal pump, especially in the pump start-up process, the channeling amount is relatively large.
　　
The balance disc automatically changes the axial clearance b between the balance disc and the balance ring when working, so as to change the pressure difference between the front and the back of the balance disc to generate a force opposite to the axial force to balance the axial force. Due to the inertia of the rotor's motion and the transient pump conditions, the running rotor will not rest at an axial equilibrium position. Balance plate is always in the state of movement around. Balance plate in normal operation of the axial channeling amount is only 0105 ~ 011mm, to meet the requirements of the mechanical seal to allow axial channeling amount of 015mm, but the balance plate in the pump start, stop, the case of drastic changes in the axial direction may greatly exceed Allowable mechanical seal axial channeling.
　　
Industrial pump after a long run, the balance disc and the balance ring friction and wear, gap b with the increase of mechanical seal axial channeling increased. As a result of the axial force, the suction side of the sealing surface of the pressing force increases, the sealing surface wear increased, until the sealing surface damage, loss of sealing effect. Spit out the side of the mechanical seal, with the wear of the balance plate, the axial component of the rotor is greater than the axial channeling required by the seal, the sealing surface of the pressing force decreases, not to seal requirements, and ultimately the pump on both sides of Mechanical seal all lose seal.
　　
2 axial force is too large
　　
Mechanical seal in the course of the process can not afford the axial force, if the presence of axial force, the impact on the mechanical seal is serious. Sometimes due to the pump axial force balance mechanism design unreasonable and manufacturing, installation, use and other reasons, resulting in axial force has not been balanced out. The mechanical seal withstands an axial force and the seal gland temperature will be high during operation. For polypropylene media, it will melt at high temperatures, so the pump will lose seal soon after it is started and when the pump is at a standstill, the seal faces will appear Intermittent jet leakage phenomenon.
　　
3 pump shaft deflection is large
　　
Mechanical seal, also known as the end seal, is a rotary axial contact type dynamic seal, which is in the fluid medium and the elastic element under the action of two perpendicular to the axis of the seal face close fit, relative rotation, so as to achieve Sealing effect, thus requiring the seal between the force to be uniform. However, due to the unreasonable design of the pump product, when the pump shaft is operating, the deflection generated at the installation location of the mechanical seal is large, so that the stress between the sealing surfaces is not uniform, which results in poor sealing effect.
　　
4 No auxiliary flushing system or auxiliary flushing system is not set properly
　　
Mechanical seal auxiliary flushing system is very important, it can effectively protect the sealing surface, play a cooling, lubrication, washed away debris and so on. Sometimes the designer does not configure the auxiliary flushing system reasonably and can not achieve the sealing effect. Sometimes, although the designer designs the auxiliary system, due to the impurities in the flushing fluid, the flow of the flushing fluid, the insufficient pressure and the irrational design of the flushing port, , Also failed to seal the same effect.
　　
5 Vibration is too large
　　
Mechanical seal vibration is too large, eventually leading to loss of sealing effect. However, the reasons for the large mechanical seal vibration is often not the cause of the mechanical seal itself, the pump is the root cause of other parts of the vibration, such as the pump shaft design is not reasonable, the reasons for processing, bearing accuracy is not enough, Radial force and other reasons.
　　
6 pump cavitation causes
　　
Due to the unreasonable operation of the device system and the poor cavitation performance of the pump inlet, the pump speed is high and local cavitation occurs at the inlet of the pump. After the cavitation occurs, there will be bubbles in the water which will impact the mechanical sealing surface On the other hand, the moving film of the anastomosis surface of the static and dynamic rings also contains air bubbles and can not form a stable flowing film, resulting in the dry friction of the anastomosis surface of the static and dynamic rings and damaging the mechanical sealing device.
　　
7 machining accuracy is not enough
　　
Machining accuracy is not enough, for many reasons, some mechanical seal itself is not enough precision, the reasons for this easy to attract the attention of people, but also easy to find. But sometimes the other parts of the pump processing accuracy is not enough, this reason, not easy to arouse people's attention. For example: pump shaft, bushings, pump body, seal the accuracy of the cavity is not enough and other reasons. The existence of these reasons is very detrimental to the sealing effect of the mechanical seal.
Industrial Pump Mechanical Seal Failure External Causes
1 axis of the axial channeling large