A large axial axial displacement of the mechanical seal sealing surface to have a certain pressure, so as to play a sealing effect, which requires the mechanical seal spring to have a certain amount of compression to the sealing end of a thrust, spin up The sealing surface to produce the required pressure seal. In order to ensure this a specific pressure, the mechanical seal requires the shaft can not have too much channeling amount, generally to ensure that within 0.5 mm. 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 of only 0105 ~ 011 mm, to meet the mechanical seal to allow the axial channeling amount of 015 mm requirements, but the balance plate in the pump start, stop, the case of sudden change in the amount of axial channeling may Greatly exceeded the allowable mechanical seal axial channeling amount. 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 withstand the axial force, if the presence of axial force, the mechanical seal on the impact 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 large deflection shaft pump Mechanical seal, also known as the end seal is a rotary axial contact type dynamic seal, which is in the fluid medium and elastic elements under the action of two perpendicular to the axis of the seal face close Together, the relative rotation, so as to achieve the sealing effect, thus requiring two seals to force evenly. 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 set unreasonable mechanical seal auxiliary flushing system is very important, it can effectively protect the sealing surface, play 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 unreasonable system operation of the device and the pump inlet cavitation performance is not good, the pump speed is high, the local cavitation at the pump entrance, cavitation occurs, there will be bubbles in the water, it on the one hand Will impact the mechanical seal surface of the outer surface, so that the surface damage; the other will make the dynamic and static ring surface of the film also contains bubbles in the flow, can not form a stable flow film, resulting in static and dynamic ring of the match surface dry friction, Damage to the mechanical seal. 7 machining accuracy is not enough machining accuracy is not enough for many reasons, some mechanical seal itself is not enough precision, this cause is 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.