The seal between the rotating pump shaft and the fixed pump housing is called the shaft seal. Its function is to prevent the high-pressure liquid from leaking out from the pump along the shaft, or the external air leaking inside along the shaft. Shaft seal of the centrifugal pump belongs to the dynamic seal. According to whether or not the sealing joints are contacted, it can be divided into contact dynamic seal and non-contact dynamic seal. The sealing device with contact dynamic seal is in contact with the shaft, and there is a relative friction between them. The contact dynamic seal can be divided into packing seal and mechanical seal.
The packing seal has the advantages of simple structure, low price, and convenient maintenance. But it also has disadvantages of large leakage and great power loss. So packing seals are only used to transport general media, such as water, and generally not suitable for transporting oil and chemical media, especially valuable, explosive and toxic media.
The mechanical seal (also known as end seal) has a good sealing effect, small leakage, and long service life, but its price is high, and the requirements for its processing, installation, and maintenance are higher than that of the general seals. Mechanical seals are suitable for transporting petroleum and chemical media and can be used to transport media with various viscosity, strong causticity and contains granule. The standard API610 (Eighth Edition) of the American Petroleum Institute stipulates that, except special users, containerized mechanical seals shall be equipped.