Analysis and working principle of mechanical seal leakage in self suction centrifugal oil pump

（1） Analysis of leakage reasons for mechanical seals of self suction centrifugal pumps

1. Leakage during installation and static testing

After the installation and commissioning of mechanical seals of self suction centrifugal pumps, static testing is generally required to observe the leakage amount. If the leakage is small, it is mostly due to problems with the sealing ring of the dynamic or static ring; When the leakage is large, it indicates that there is a problem between the dynamic and static friction pairs. On the basis of preliminary observation of the leakage amount and judgment of the leakage location, manually turn the machine to observe. If there is no significant change in the leakage amount, there is a problem with the static and dynamic ring sealing rings; If there is a significant change in leakage during turning, it can be concluded that there is a problem with the friction pair between the dynamic and static rings; If the leaked medium is sprayed along the axial direction, there are more problems with the dynamic ring seal. If the leaked medium is sprayed around or leaks out of the water cooling hole, it is mostly due to the failure of the static ring seal. In addition, leakage channels can also exist simultaneously, but generally have primary and secondary differences. As long as you observe carefully, familiarize yourself with the structure, you can make a correct judgment

2. Sudden Leakage during Normal Operation

The sudden leakage of self suction centrifugal pumps during operation is caused by normal wear and tear or reaching the service life, while the majority is caused by significant changes in operating conditions or improper operation and maintenance.

(1) Evacuation, cavitation, or prolonged pressure holding can cause seal damage

(2) The actual output of the pump is too small, and a large amount of medium circulates inside the pump, causing heat accumulation and causing medium gasification, resulting in seal failure

(3) The return flow rate is too high, causing the bottom sediment of the suction pipe side containers (tower, kettle, tank, pool) to rise and damage the seal

(4) For long-term shutdowns and restarts without manual turning, the friction pair may tear the sealing surface due to adhesion

(5) An increase in corrosive, polymeric, and cementitious substances in the medium

3. Poor flushing

Due to the working characteristics of self suction centrifugal pumps, the friction between the moving and stationary ring end faces will continuously generate frictional heat, causing an increase in temperature inside the friction pair, resulting in the following effects:

(1) Dry friction caused by the evaporation and vaporization of the liquid film inside the friction pair;

(2) The viscosity of the liquid film inside the friction pair decreases, resulting in poor lubrication

(3) The vapor pressure of the friction pair medium increases, resulting in leakage

(II) Working principle of self suction centrifugal oil pump

Self suction centrifugal oil pump is a device that uses the high-speed rotation of the impeller to transfer force to the liquid. The driving machine drives the impeller to rotate through the pump shaft to generate centrifugal force. Under the action of centrifugal force, the liquid's speed and pressure are enhanced, and it is thrown towards the outlet of the impeller along the impeller blade flow channel. As the liquid flows in from the impeller port, its own speed and pressure increase. It is collected through the design of the volute and sent to the discharge pipe. Most of the speed of the liquid discharged by the impeller will be converted into pressure energy, relying on this energy to transport the liquid to the work site.

. As the liquid is thrown towards the outlet of the impeller, a low pressure will form at the center of the impeller inlet, creating a pressure deviation between the liquid in the suction tank and the impeller. Due to the pressure effect, the liquid in the suction tank will enter the impeller through the suction pipeline and the suction chamber of the self suction centrifugal pump. Through this process, the impeller will continuously suck in and discharge the liquid, generating operational benefits. The working process is actually a process of energy conversion and transmission. Convert the mechanical energy generated by the high-speed rotation of the electric motor into the kinetic and potential energy of the extracted water