A complete set of machine seals is composed of two forms of seals: dynamic seals and static seals, both of which are indispensable. The commonly used type in centrifugal slurry pumps is the containerized double end face machine seal, which has a total of 5 sealing points (see figure below). The dynamic seal relies on the close contact between the two sealing end faces to maintain the seal during rotation, while the static seal mainly relies on the rubber sealing ring of the machine seal to maintain the seal between the dynamic ring and the shaft sleeve under slight movement.

1- Friction pair sealing end face of dynamic and static rings 2- Static ring sealing ring 3- Cover sealing area
4- Sealing between shaft sleeve and shaft 5- Sealing ring between shaft sleeve and dynamic ring
The leakage of the centrifugal slurry pump seal is mainly caused by three sealing problems.
(1) Rubber sealing ring for machine sealing
The medium temperature conveyed by the centrifugal slurry pump is relatively high, which can cause the high-temperature transmission of the medium and keep the mechanical seal in a high-temperature state for a long time. Especially after the pump is running, the high-speed rotation and friction heating of the sealing end face of the mechanical seal can cause aging or deformation of the rubber sealing ring. In order to reduce the operating temperature of the machine seal, the slurry pump needs to supply cooling water to the machine seal during operation, which is used for cooling the machine seal. However, the hardness of the machine seal cooling water and the impurities contained in the water can gradually cause damage to the rubber seal ring or reduce its sealing effect.
(2) Sealing ring compression spring
The compression spring is responsible for providing elastic compensation for the dynamic ring. Due to the presence of cooling water, the mechanical seal will produce a large amount of scale after a certain period of use, which will affect the performance of the compression spring, causing the sealing end faces of the dynamic and static rings of the mechanical seal to not fit tightly, resulting in gaps between the sealing end faces of the mechanical seal and leakage.
(3) Damaged machine seal end face
The end face of the machine seal is generally made of very wear-resistant materials such as hard alloy or silicon carbide, and the structure of the commonly used containerized machine seal also greatly reduces the impact factors on the end face. Therefore, under normal use, the end face of the machine seal is difficult to break and damage due to external force impact on the end face.
To diagnose the cause of seal leakage and identify the location of the leakage, analysis and judgment can be made based on the static leakage test after seal assembly and the leakage situation after seal rotation. If the machine seal is in a stationary state after installation and there is a small amount of leakage when a certain pressure of cooling water is introduced, the problem is generally caused by the sealing rings at the dynamic and static rings of the machine seal; If the leakage of the machine seal is large after the introduction of cooling water, it indicates that there is a problem with the end face sealing between the moving ring and the stationary ring. This is usually caused by the inability of the two end faces to fully fit, and this fault requires disassembly and reinstallation of the machine seal; If there is no leakage during the initial stage of the machine seal, but leakage occurs after a period of operation, it is usually caused by the failure of the compression spring of the machine seal or damage to the dynamic ring of the machine seal. In addition, the cause of the seal failure can be determined and corresponding maintenance plans can be formulated based on the operating status of the slurry pump, the vibration value and speed of the equipment, the quality of the cooling water, and the operating time of the seal.