Reasons For Mechanical Seal Leakage in Centrifugal Pumps

The shutdown of centrifugal pumps is mainly caused by the failure of mechanical seals. The main manifestation of failure is leakage, which can be caused by the following reasons:
1. The main reasons for the leakage of the sealing surface of the dynamic and static rings are: the flatness and roughness of the end face do not meet the requirements, or there are scratches on the surface; There is particulate matter between the end faces, causing the two end faces to not run equally; Installation is not in place and the method is incorrect.
2. The main reasons for the leakage of the compensating ring sealing ring are: deformation of the pressure cover and uneven pre tightening force; Incorrect installation; The quality of the sealing ring does not meet the standards; The selection of sealing ring is incorrect.

The actual use effect shows that the most frequently failed sealing components are the end faces of the dynamic and static rings. Cracking on the end faces of the dynamic and static rings in centrifugal pumps is a common failure phenomenon, mainly due to:
1. The gap between the sealing surfaces during installation is too large, and the flushing solution cannot take away the heat generated by the friction pair in time; The flushing liquid leaked from the gap between the sealing surfaces, causing overheating and damage to the end faces.
2. The vaporization and expansion of liquid media cause the two end faces to separate due to the vaporization and expansion force. When the two sealing surfaces are tightly adhered, the lubricating film is damaged, resulting in overheating of the end face surface.
3. The lubricity of liquid media is poor, and coupled with operating pressure overload, the two sealing surfaces do not track and rotate synchronously. For example, a high-speed pump with a speed of 20445r/min and a center diameter of 7cm on the sealing surface has a linear velocity of up to 75m/s after operation. When one of the sealing surfaces lags behind and cannot track rotation, the instantaneous high temperature causes damage to the sealing surface.
4. The sealing flushing liquid orifice plate or filter screen is blocked, causing insufficient water flow and resulting in the failure of the machine seal.

In addition, the sliding grooves on the sealing surface and the gaps that appear when the end faces are in contact can cause the sealing components to fail. The main reasons are:
1. The liquid medium is not clean and contains tiny hard particles that slide into the sealing surface at a high speed, scratching the surface of the end face and causing failure.
2. The coaxiality of the transmission components of the pump is poor. After the pump is turned on, the end face is rubbed and shaken once every revolution, and the trajectory of the moving ring is not concentric, resulting in end face vaporization and overheating wear.
3. The frequent occurrence of hydraulic characteristics of liquid media causes vibration of the pump unit, resulting in misalignment of the sealing surface and failure.
Corrosion of sealing components by liquid media, stress concentration, compatibility of soft and hard materials, erosion, incompatibility between auxiliary seals such as O-ring, V-ring, concave ring and liquid media, deformation, etc. can all cause surface damage and failure of mechanical seals. Therefore, a comprehensive analysis of the damage forms should be conducted to identify the root cause and ensure long-term operation of mechanical seals.