Pump Mechanical Seal Leakage Point Analysis and Maintenance Methods

Pump with a wide range of mechanical seals, different models, but the leak there are five main points:
(L) seal between sleeve and shaft;
(2) between the moving ring and the shaft sleeve seal;
(3) moving, static seal between;
(4) between the static ring and static ring seat seal;
(5) seal between the cover and the pump body.

First, the leak analysis and judgment

1. Leakage during static test. Mechanical seal installation and commissioning is good, the general should be static test, observe the amount of leakage. If the leakage is small, mostly ring or static ring seal problems; leakage is large, then that dynamic and static friction ring there is a problem. In the initial observation of the leakage, to determine the leakage site, based on manual observation disk, if the leakage was no significant changes in the static and dynamic ring seal problems; such as the disk when there is a significant change in leakage can be concluded that the move, Static friction ring there is a problem; such as the leakage of media along the axial injection, the dynamic ring seal there are many problems, leakage to the surrounding medium jet or water leakage from the hole, the more static ring failure. In addition, the leak channel can exist at the same time, but generally there are major and minor differences, as long as careful observation, familiar with the structure, we must be able to correctly judge.
2. Leakage during commissioning. Pump mechanical seal after static test, the centrifugal force generated by high-speed rotation of the operation, will inhibit the media leakage. Therefore, the test run when the mechanical seal leakage excludes the seal between the shaft and the end cover, basically due to dynamic and static friction ring caused by damage. The factors that cause the failure of friction seal are:
(L) operation, due to taking the time, cavitation, pressure and other anomalies, causing greater axial force, so that dynamic and static contact surface separation;
(2) The excessive compression when installing the mechanical seal, resulting in serious wear and abrasion of the friction end face;
(3) ring seal is too tight, the spring can not adjust the axial amount of floating ring;
(4) static ring seal is too loose, when the moving ring axial float, the static ring from the static ring seat;
(5) There is granular material in the working medium, and it enters into the friction pair during operation.
(6) design and selection is wrong, the seal face lower than the pressure or sealing material shrinkage larger. These phenomena often appear in the trial operation, and sometimes can be eliminated by adjusting the static ring seat, etc., but most need to re-disassemble, replace the seal.
3. Suddenly leak during normal operation. Sudden leakage of centrifugal pump in operation a few due to normal wear and tear or have reached the service life, most of which is due to larger changes in conditions or operation and maintenance caused by improper.
(1) evacuating, cavitation or pressure holding for a long time, leading to seal damage;
(2) the actual output of the pump is too small, a large number of medium pump cycle, heat accumulation, causing gasification of the medium, resulting in seal failure;
(3) return flow is too large, resulting in inhalation tube side of the container (tower, kettle, tank, pool) at the bottom of sediment damage, damage to the seal;
(4) for a long time outage, restart without manual turning, friction due to adhesion and tear the sealing surface;
(5) Medium corrosive, polymeric, colloidal substances increased;
(6) rapid changes in ambient temperature;
(7) Frequent changes in operating conditions or adjustments;
(8) Sudden power failure or downtime and so on. Centrifugal pump in normal operation, a sudden leak, if not found in time, often lead to a larger accident or loss, we must pay attention to and take effective measures.

Second, pump mechanical seal maintenance in several errors

1. The larger the spring compression, the better the sealing effect. In actual fact, the spring compression is too large, can lead to rapid wear and tear of the friction pair, instantaneous burning; excessive compression of the spring lost the ability to adjust the dynamic ring end face, leading to seal failure.
2. Moving ring seal chart as tight as possible. In fact, the ring is too tight moving ring harmless. One is to exacerbate the wear and tear between the seal ring and the sleeve, premature leakage; the other is to increase the axial resistance of the moving ring, the resistance to movement, can not be adjusted in time when the working conditions change frequently; thirdly, Is to move the ring ring deformation, affecting the sealing effect.
3. Static ring seal as tight as possible. Static ring seal is basically static, the relatively tight seal will be better, but too tight is also harmful. First, the static ring seal caused by over-deformation, affecting the sealing effect; Second, static graphite material to the majority, generally more brittle, excessive stress can easily cause fragmentation; Third, the installation and removal difficulties, can easily damage the static ring.
4. Impeller lock mother tighter and better. Mechanical seal leakage, the sleeve and shaft leakage (shaft leakage) is more common. Generally believed that the leakage between the shaft impeller lock is not locked, in fact, leading to leakage between the shaft more factors, such as the shaft pad failure, offset, impurities within the shaft, shaft and sleeve with a larger shape Bit error, contact surface damage, there is a gap between the various components on the shaft, the shaft thread is too long and so will lead to shaft leakage. Lock over lock only lead to premature failure of the shaft pad, on the contrary, lock the lock body, so that the shaft pad always maintain a certain degree of compression flexibility, in operation, the lock will automatically lock in time, the shaft is always in good Sealed state.
5. New better than the old. Relatively speaking, the use of new mechanical seal effect is better than the old, but the new mechanical seal quality or material selection is not appropriate, with the larger size error will affect the sealing effect; In polymeric and permeability medium, the static ring without excessive Wear, or not replaced as well. Because the static ring in the static ring seat for a long time in a quiescent state, the polymer and impurities deposited as one, played a better seal.
6. Disassembly is better than not demolished. In the event of a mechanical seal leak eager to repair, in fact, sometimes the seal is not damaged, just adjust the condition or adjust the seal to eliminate leakage. This will not only avoid waste but also to verify their own ability to judge the failure to accumulate maintenance experience to improve the quality of maintenance.

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