Several Causes for Mechanical Seal Leakage of Mechanical Seal for Pump of Desulfurization

The desulfurization pump is a cantilevered single-stage single-suction centrifugal pump designed and developed to transport corrosive media with fine particles. The pump is made of steel-lined ultra-high molecular weight polyethylene, which is currently the new generation of pump-resistant and wear-resistant engineering plastics. Its outstanding advantages are superior wear resistance, impact resistance (especially low-temperature resistance), creep resistance (resistant to environmental stress cracking), and corrosion resistance among all plastics. The analysis and judgment of mechanical seal leakage of desulfurization pump are as follows.

Leakage of mechanical seal for pump during static pressure test

After installing and commissioning the mechanical seal for pump, a static pressure test should be carried out to observe the leakage. If the leakage is small, the sealing ring of the moving ring or the static ring will have problems. When the leakage is large, it indicates that there is a problem between the friction pairs of the moving ring and the static ring. Based on the preliminary observation of the leakage amount and the judgment of the leakage position, the turning car can be manually observed. If the leakage amount does not change significantly, it indicates that there is a problem with the sealing ring of the static ring and the moving ring. If the leakage amount changes significantly during the turning process, it can be concluded that there is a problem with the friction pair of the dynamic and static rings. If the leaking medium is sprayed along the axial direction, the sealing ring of the moving ring usually has problems. If the leaked medium is sprayed around the water cooling hole or leaks out from the water cooling hole, the sealing ring of the static ring will mostly fail.

Leakage of mechanical seal for pump during trial operation

After the static pressure test of the mechanical seal of the power plant desulfurization pump, the centrifugal force generated by high-speed rotation will inhibit the leakage of the medium. Therefore, the leakage of the mechanical seal during the trial operation is mainly caused by the failure of the friction between the moving ring and the static ring after the failure of the seal between the shaft and the end cover is eliminated. The main factors that cause the failure of the friction pair seal are:

• During the operation, abnormal phenomena such as vacuum pumping, cavitation, and pressure maintenance cause a larger axial force between the contact surfaces of the moving and static rings.

• When installing the mechanical seal, over-compression will cause serious wear and scratching of the end faces of the friction pairs.
  

• The sealing ring of the moving ring is too tight, and the spring cannot adjust the axial float of the moving ring.
  

• The sealing ring of the stationary ring is too loose. When the moving ring floats along the axial direction, the stationary ring will escape from the stationary seat.
  

• The particulate matter in the working medium enters the friction pair during operation and damages the end faces of the actuator and the sealing ring.
  

• Incorrect design and selection, low specific pressure of the sealing end face, or large cold shrinkage of the sealing material. These phenomena usually occur during trial operation, and some can be eliminated by adjusting the stationary seat appropriately, but most of them require reassembly and replacement of the sealing components.
  

Sudden leakage of mechanical seal for pump during normal operation 

Some reasons for sudden leakage of mechanical seal for pump during operation of power plant desulfurization pump are normal wear and reaching the end of service life, while most are caused by significant changes in working conditions or improper operation and maintenance, including the following:

• Increase in corrosive, polymerized, and gelatinous substances in the medium.

• Sudden changes in ambient temperature.
  

• Frequent changes or adjustments in working conditions.
  

• Sudden power failure and equipment shutdown.
  

• Long pumping, cavitation, or pressure maintenance time causing seal damage.
  

• High reflux will cause sediment at the bottom of the container (tower, box, and water tank) on the suction side to rise and damage the seal.
  

• Failure to manually rotate the machine after a long shutdown and restart, resulting in friction adhesion and tearing of the seal faces.