Filling Seals

Definition of Packing Seal
Filler seals, also known as gland packings, are commonly referred to as packing seals. Packing seals are an ancient type of seal structure, where in ancient China, cotton yarn was used to plug leaks in water-lifting machinery. The earliest steam engines in the world also employed this sealing method. The production and development of oil extraction technology in the 19th century led to new advancements in the materials used for filler seals. By the 20th century, filler seals gained popularity across many industrial sectors due to their simple structure, affordability, and wide availability.

Principle of Filling Sealing
After the packing is inserted into the packing chamber, it is axially compressed by the pressure cap screw. When there is relative motion between the shaft and the packing, due to the plasticity of the packing, it generates radial force and comes into close contact with the shaft. At the same time, the lubricant soaked in the packing is extruded, forming an oil film between the contact surfaces. Since the contact state is not particularly uniform, the contact areas enter a "boundary lubrication" state, known as the "bearing effect"; while the uncontacted concave areas form small oil grooves with thicker oil films. The contact and non-contact areas form an irregular labyrinth, which serves to prevent fluid leakage, known as the "labyrinth effect." This is the mechanism of packing sealing. Clearly, good sealing relies on maintaining both the "bearing effect" and the "labyrinth effect." That is, it is necessary to maintain good lubrication and proper tension. Poor lubrication or excessive tension can break the oil film, causing dry friction between the packing and the shaft, leading to shaft burning and severe wear.
To achieve this, it is necessary to frequently adjust the compression of the filling material so that after the lubricant within the filling has been depleted over time, additional lubricant can be extruded. This also compensates for the relaxation of compression due to volume changes in the filling. Clearly, frequently squeezing the filling will deplete the impregnant, thus regular replacement of the filling is essential. Additionally, to maintain a liquid film and dissipate friction heat, it is also necessary to intentionally allow for a small amount of leakage at the filling area.