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Analysis of causes of mechanical seal failure


Mechanical seal for pump refers to a device installed and operated in pump equipment to perform a dynamic sealing function to prevent the fluid medium in the volute of the water pump from flowing out through the pump shaft and to mechanically seal the outside of the water pump.


Centrifugal pump shutdown is mainly caused by the failure of mechanical seals. Most of the symptoms of failure are leaks, and the causes of leaks are as follows:


1. Leakage of dynamic and static ring sealing surfaces


The main reasons are: the flatness and roughness of the end face do not meet the requirements, or the surface is scratched; there are particulate matter between the end faces, causing the two end faces to not operate equally; the installation is not in place and the method is incorrect.


2. Compensation ring seal leakage


The main reasons are: gland deformation, uneven preload force; incorrect installation; sealing ring quality does not meet standards; sealing ring selection is incorrect.


The most common parts of the sealing element failure are the end faces of the dynamic and static rings. Cracks on the end faces of the dynamic and static rings of centrifugal pumps are common failure phenomena. The main reasons are:


1. The gap between the sealing surfaces is too large during installation


The flushing fluid is too late to take away the heat generated by the friction pair; the flushing fluid leaks from the gap between the sealing surfaces, causing the end face to overheat and be damaged.


2. Vaporization and expansion of liquid medium


The two end faces are separated by the vaporization expansion force. When the two sealing faces are forced to fit together, the lubricating film is destroyed and the end face surface is overheated.


3. Liquid medium has poor lubricity


When the operating pressure is overloaded, the two sealing surfaces will track and rotate out of synchronization. When one sealing surface lags behind and cannot track the rotation, the instantaneous high temperature will cause damage to the sealing surface.


The orifice plate or filter of the seal flushing liquid is clogged, resulting in insufficient water and causing the mechanical seal to fail. There are sliding grooves on the surface of the sealing surface, and gaps appear when the end faces are attached, resulting in the failure of the sealing element. The main reasons are:


1. The liquid medium is not clean


There are tiny hard particles that slide onto the sealing surface at a very high speed, scratching the end surface and causing it to fail.


2. Poor coaxiality of pump transmission parts


After the pump is turned on, the end face is shaken and rubbed once every revolution, and the moving track of the moving ring is not concentric, causing the end face to vaporize and overheat and wear.


3.Sealing surface misalignment failure


Corrosion of sealing elements by liquid medium, stress concentration, combination of soft and hard materials, erosion, auxiliary sealing O-rings, V-rings, concave rings and liquid medium incompatibility, deformation, etc. will all cause damage to the mechanical seal surface, so The damage pattern must be comprehensively analyzed to find out the root cause and ensure the long-term operation of the mechanical seal.

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