Filling Seals

Definition of Packing Seal

Filler seals, also known as gland packings seals, are commonly referred to as packing seals. Packing seals are an ancient type of seal structure; in ancient China, they were used to stop leaks in water-lifting machinery by packing cotton yarn. The steam engines that appeared in the world also adopted 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 had gained favor in many industrial sectors due to their simple structure, reasonable price, and wide availability.

Principle of Packing 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 into the packing is extruded, forming an oil film between the contacting surfaces. Since the contact state is not particularly uniform, "boundary lubrication" occurs at the contacting areas, referred to as "bearing effect"; while the uncontacted concave areas form small oil grooves with thicker oil films. The contacting and non-contacting areas form an irregular labyrinth, which prevents fluid leakage. This is called "labyrinth effect." This is the mechanism of packing sealing. Clearly, good sealing depends on maintaining both the "bearing effect" and the "labyrinth effect." In other words, it is necessary to maintain good lubrication and proper tightness. Poor lubrication or excessive tightness can break the oil film, causing dry friction between the packing and the shaft, leading to shaft burning and severe wear.
To address this, it is necessary to frequently adjust the compression of the packing material so that after some time of operation and the loss of lubricant within the packing, additional lubricant can be extruded. This also compensates for the relaxation of compression due to volume changes in the packing. Clearly, frequently squeezing the packing will deplete the impregnant, thus regular replacement of the packing 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 packing area.