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Analysis of the reasons for the shutdown of the desalinated water pump due to the failure of the mechanical seal

09 Apr 2021Email

The shutdown of the desalinated water pump is mainly caused by the failure of the mechanical seal. Most of the failure manifestations are leakage, and the reasons for leakage are as follows:

Demineralized water pump

① The main reasons for the leakage of the sealing surface of the dynamic and static rings are: the flatness of the end surface, the roughness does not meet the requirements, or the surface is scratched; there is particulate matter between the end surfaces, which causes the two ends to not operate at the same time; the installation is not in place and the method is incorrect.

② The sealing ring of the compensation ring leaks. The main reasons are: the gland is deformed and the pre-tightening force is uneven; the installation is not correct; the quality of the sealing ring does not meet the standard; the type of the sealing ring is incorrect.

 

The actual use results show that the most failure of the sealing element is the end face of the dynamic and static ring. The crack on the end face of the dynamic and static ring of the centrifugal pump is a common failure phenomenon. The main reasons are:

①The sealing surface gap is too large during installation, and the flushing fluid is too late to take away the heat generated by the friction pair; the flushing fluid leaks from the sealing surface gap, causing the end surface to be overheated and damaged.

② The liquid medium vaporizes and expands, so that the two ends are separated by the vaporization and expansion force. When the two sealing surfaces are firmly attached, the lubricating film is destroyed and the end surface is overheated.

③The liquid medium has poor lubricity, and the operating pressure is overloaded, and the tracking and rotation of the two sealing surfaces are not synchronized. For example, the high-speed pump speed is 20445r/min, the center diameter of the sealing surface is 7cm, and the linear speed of the pump is as high as 75 m/s after the pump is running. When a sealing surface lags behind and cannot follow the rotation, the instantaneous high temperature causes the sealing surface to be damaged.

④ The orifice plate or filter screen of the sealing flushing fluid is blocked, resulting in insufficient water volume and failure of the mechanical seal.

 

In addition, the sliding grooves on the sealing surface and the gaps in the end faces caused the failure of the sealing element. The main reasons are:

①The liquid medium is not clean and has tiny hard particles. It slides on the sealing surface at a very high speed and scratches the end surface and becomes invalid.

②The coaxiality of the transmission parts of the machine and pump is poor. After the pump is turned on, the end face is swayed and rubbed once per revolution, and the moving trajectory of the moving ring is not concentric, causing the end face to vaporize and overheat and wear.

③ The frequent occurrence of hydraulic characteristics of the liquid medium causes the pump unit to vibrate, causing the sealing surface to be misaligned and fail.
The corrosion of the sealing element by the liquid medium, the stress concentration, the coordination of soft and hard materials, erosion, auxiliary sealing O-ring, V-ring, concave ring and liquid medium incompatibility, deformation, etc. will cause damage and failure of the mechanical seal surface, so The damage form should be analyzed comprehensively to find the root cause to ensure the long-term operation of the mechanical seal

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