Exploring the principle of shaft seal technology for slurry pumps

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• TIME : 2025-07-02

Definition and function of shaft seal

When a slurry pump transports slurry, there is a pressure difference between the fluid inside the pump and the atmosphere outside the pump, and the fluid will leak outward along the gap between the shaft and the shell. Therefore, a sealing device is required, which is called a shaft seal. Shaft seals are not only used in slurry pumps, but are also commonly used in centrifugal pumps. Its main function is to prevent both the leakage of medium inside the pump and the leakage of air outside the pump into the pump.

Common forms and principles of shaft seals

packing seal

Working principle: Insert a packing (such as butter boiled cotton thread or carbon fiber impregnated polytetrafluoroethylene) into the stuffing box, adjust the compression degree through a nut, and then inject shaft seal water. Use the shaft seal water as a sealing liquid medium to seal, lubricate, and cool down. The shaft seal water can flow into the pump to prevent slurry from overflowing from the shaft seal, thereby preventing wear and corrosion of the shaft and submersible pump shaft seals. Packing sealing relies on the soft and hard wear between the packing and the shaft sleeve to achieve a sealing effect.

Usage: It is commonly used in slurry pumps that do not require extremely high sealing requirements. Some slurry pumps under normal operating conditions will use this shaft seal form, but it requires regular maintenance and replacement of packing.

Auxiliary impeller power seal

Working principle: The secondary impeller rotates together with the pump shaft, and the liquid in the secondary impeller also rotates together, generating an outward centrifugal force. This centrifugal force can balance the pressure of the medium inside the pump and prevent the medium from leaking to the shaft seal. At the same time, it can also reduce the pressure at the packing seal or mechanical seal, reducing the burden on the seal.

Usage: It is usually used in conjunction with packing seals. Some slurry pumps with high shaft seal requirements and high conveying medium pressure will adopt this combination form, such as pumps used in mining, power and other industries to transport slurry containing large particles and high pressure.

mechanical seal

Working principle: Mechanical seal relies on the tight friction between the dynamic and static rings of the mechanical seal to achieve a sealing effect, which transforms the axial seal into an end face seal between the dynamic and static rings. The mechanical seal used in the slurry pump of the coal preparation plant belongs to the water injection external flushing mechanical seal, which requires the addition of shaft seal water. The shaft seal water mainly plays a cooling and lubricating role to prevent dry friction between the dynamic and static rings from burning out the seal. At the same time, mechanical seals require no residue inside the seal. Before assembling the mechanical seal, components such as the moving ring, stationary ring, and shaft sleeve should be cleaned, and the surface of the moving and stationary rings should be checked for scratches, cracks, and other defects that can cause serious leakage of the seal.

Usage: In the past, it was widely used in clean water pumps, but it was later applied in slurry pumps that transport abrasive slurries containing solid particles. At present, with the joint efforts of slurry pump manufacturers and mechanical seal manufacturers, its excellent performance is increasingly widely used in slurry pumps.

The function and principle of shaft seal water

role

Reduce reflux loss and improve efficiency: It can reduce high-pressure water reflux loss and improve water pump efficiency.

Preventing wear and corrosion: After the slurry is pressurized by the impeller, it will leak from the shaft seal or accumulate in the dynamic and static clearances of the shaft seal, causing wear and corrosion. The shaft seal water can flow into the pump to prevent slurry from overflowing from the shaft seal, thereby preventing wear and corrosion of the shaft and submersible pump shaft seals. In addition, introducing shaft seal water between the pump casing and the submersible pump slurry pump inner shell can prevent slurry from entering the gap between the inner shell and the outer shell, and can also extend the service life of the pump's related accessories.

Convenient maintenance and replacement: to a certain extent, it facilitates the maintenance and replacement of shaft seal components.

principle

Different forms of shaft seals have different requirements for shaft seal water pressure. A slurry pump with a secondary impeller generally takes 1/2 of the pump outlet pressure p, as the secondary impeller drives the liquid inside the chamber to also serve as a certain shaft seal; Fill sealed slurry pump and mechanical seal pump are set at 2/3p. Mechanical seal pump is usually the main pump, and the pressure is set at around 2/3p. However, the outlet pressure (p is a variable) of the slurry pump in the coal preparation plant is different. For example, the pressure of the bottom flow pump of the concentrator is higher (with a head of up to 80m), while some pumps such as the circulating water pump have a head of only over 40 meters. Therefore, supplying shaft seal water to all slurry pumps in the plant at one pressure is not the best solution.

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(Editor in charge: Slurry Pump https://www.fuyangpumps.com/)

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