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What Are The Maintenance Methods For Pump Mechanical Seals?
Apr 02, 2018

What are the maintenance methods for pump mechanical seals?

What are the maintenance methods for pump mechanical seals? There are a wide variety of pump mechanical seals, with different models, but there are five major leaks:

     (1) Sealing between shaft sleeve and shaft;

     (2) The seal between the moving ring and the sleeve;

     (3) Sealing between moving and stationary rings;

     (4) The seal between the stationary ring and the stationary ring seat;

     (5) The seal between the seal cap and the pump body.

     Generally speaking, the leakage between the shaft sleeves and the sealed end caps and the pump body is easy to find and solve, but it requires careful observation, especially when the working medium is liquefied gas or high-pressure, toxic and harmful gases, it is relatively difficult some. The remaining leaks are intuitively difficult to distinguish and judge, and on the basis of long-term management and maintenance practices, leakage symptoms must be observed, analyzed, and judged in order to draw correct conclusions.

First, the leakage analysis and judgment

    1. Leak during installation test. After installation and debugging of mechanical seals, it is generally necessary to conduct a static test to observe the leakage. If the leakage is small, there are problems with the moving ring or the static ring seal ring; when the leakage amount is large, it indicates that there is a problem between the friction pair of the dynamic and static rings. After initially observing the leakage amount and judging the leakage location, observe the manual operation. If there is no significant change in the leakage amount, there will be problems with the static and dynamic ring seal rings; if the leakage amount of the disc brakes changes significantly, it can be concluded that There are problems with the static ring friction pair; if the leakage medium is ejected in the axial direction, there are many problems with the dynamic ring seal ring. If the leaking medium is injected around or leaks from the water cooling hole, the static seal ring is mostly ineffective. In addition, leakage channels can also exist at the same time, but there are generally differences between the primary and secondary, as long as the observation of detailed, familiar with the structure, we can certainly determine correctly.

   2. Leakage during commissioning. After the mechanical seal of the pump is subjected to a static test, the centrifugal force generated by the high-speed rotation during operation will suppress the leakage of the medium. Therefore, the leakage of the mechanical seal during the trial operation after eliminating the shaft and the seal failure of the end cap is basically caused by the damage of the friction and static pair of the dynamic and static rings. The main factors causing the failure of the friction pair seal are:

    (1) In operation, due to anomalies such as evacuation, cavitation, and pressure, large axial forces are caused and the moving and stationary ring contact surfaces are separated;

    (2) excessive compression of the mechanical seal during installation, resulting in serious wear and scratches on the frictional end face;

    (3) The ring seal is too tight and the spring cannot adjust the axial float of the ring;

    (4) The static ring seal ring is too loose. When the ring moves axially, the static ring disengages from the stationary ring seat;

    (5) There are granular substances in the working medium, and the friction pair in operation, the detection of moving and static sealing end face;

    (6) The design selection is wrong, the pressure ratio of the seal end face is lower or the sealing material is more cold-shrinkable. The above phenomenon often occurs during the test run, and sometimes it can be eliminated by adjusting the static seat etc., but most of them need to be disassembled and replaced.

   3. Sudden leakage during normal operation. A sudden loss of a few centrifugal pumps during operation is due to normal wear or has reached the service life, and most of them are caused by large changes in operating conditions or due to improper operation or maintenance.

     (1) evacuation, cavitation, or pressure for a long time, resulting in damage to the seal;

     (2) The actual output of the pump is too small, a large number of medium pumps circulate, and heat accumulates, causing gasification of the medium, resulting in seal failure;

     (3) The return flow rate is too large, causing the bottom of the suction-side tube (towers, kettles, tanks, and pools) to lift up and damage the seal.

     (4) For a long time outage, there is no manual disc brake when re-starting, and the friction face tears the sealing surface due to adhesion;

     (5) Increased corrosive, polymeric, gel-binding substances in the medium;

     (6) Rapid changes in ambient temperature;

     (7) Frequent changes or adjustments in operating conditions;

     (8) Sudden power failure or downtime. Centrifugal pump suddenly leaks during normal operation. If it cannot be discovered in time, it often leads to a larger accident or loss. Attention must be given and effective measures must be taken.

Second, several errors in the maintenance of pump mechanical seals

     1. The greater the amount of spring compression, the better the sealing effect. Actually, excessive spring compression can lead to rapid wear of the friction pair and instant burnout. Excessive compression causes the spring to lose its ability to adjust the end face of the moving ring, resulting in failure of the seal.

     2. The tighter the dynamic ring seal, the better. In fact, the dynamic ring seal is too harmful and harmful. One is to intensify the wear between the seal ring and the sleeve and cause premature leakage; the other is to increase the axial adjustment of the moving ring and the resistance of the movement. When the working conditions change frequently, it cannot be adjusted timely; third, the spring is fatigued and easily damaged; The deformation of the dynamic ring seal affects the sealing effect.

    3. The tighter the ring seal, the better. The static ring seal is basically in a stationary state, and the relatively tight seal effect will be better, but too tight is also harmful. The first is caused by excessive deformation of the static ring seal, affecting the sealing effect; Second, the static ring material is mostly graphite, generally more brittle, excessive stress can easily cause fragmentation; Third, installation, removal difficult, very easy to damage the static ring.

    4. The tighter the impeller locks, the better. Leakage between shaft sleeves and shaft (leakage between shafts) is common in mechanical seal leakage. It is generally believed that the leakage between shafts means that the impeller lock is not locked. In fact, there are many factors that lead to leakage between shafts. For example, the inter-shaft mat fails, there is misalignment, there are impurities in the shaft, and the shaft and the shaft sleeve have large shapes. Bit error, failure of the contact surface, gaps between the parts on the shaft, and excessive shaft thread length can cause shaft leakage. Locking the female lock excessively will only lead to premature failure of the inter-shaft pad. On the contrary, it will lock the lock mother properly so that the inter-axial pad always maintains a certain compression elasticity. In operation, the female lock locks automatically so that the shaft is always in good condition. The sealed state.

    5. The new one is better than the old one. Relatively speaking, the use of new mechanical seals is better than the old ones, but the quality or material selection of new mechanical seals is not appropriate, and the larger size error will affect the sealing effect; in polymeric and osmotic media, static rings are Excessive wear, or not replaced as well.

Because the stationary ring is in a stationary state for a long time in the stationary ring seat, the polymer and the impurities are deposited as a whole, which plays a good sealing role.

    6. Renovation is better than not dismantling. Once the mechanical seal leaks, it will be eager to repair, in fact, sometimes the seal is not damaged, just adjust the working conditions or adjust the seal properly to eliminate the leak. This will not only avoid waste but also verify your own fault diagnosis capabilities, accumulate maintenance experience and improve the quality of maintenance.

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Susie Ding


Skype: susiecc0523