Sealing Principle of Packing Gland

Sealing Principle of Packing Gland

1. Sealing Principle of Packing Gland
The sealing principle of packing gland mainly relies on the labyrinth effect and the bearing effect. As a professional China C95800 Ball Valve Factory, we understand that proper sealing is crucial for valve performance. The labyrinth effect refers to the microscopic roughness of the shaft surface, which only partially fits with the packing, leaving tiny gaps in between. These gaps form a maze-like path that throttles the pressurized medium multiple times, achieving an effective seal. The bearing effect comes from a thin lubricating film formed between the shaft and the packing, which allows the packing to function similarly to a sliding bearing. This not only provides lubrication but also reduces excessive wear between the packing and the shaft.

2. Material Requirements for Packing Gland
Due to factors such as the temperature, pressure, and pH of the sealing medium, as well as the equipment’s linear speed, surface roughness, concentricity, radial run-out, and eccentricity, the packing materials are required to have the following characteristics:

1. Certain elastic-plastic properties

2. Chemical stability

3. Impermeability

4. Self-lubricating ability

5. Temperature resistance

6. Ease of installation and removal

7. Simple manufacturing and low cost

These material properties directly affect the sealing performance and service life of packing glands. However, materials that fully meet all these requirements are rare. Therefore, sourcing high-quality sealing materials and enhancing their performance has always been a key focus in the sealing industry.

3. Forms and Characteristics of Packing Glands
With the continuous advancement of production technology, the weaving methods of packing glands have become more diverse. According to different operating conditions and environments, various weaving methods directly influence sealing performance and service life. The main weaving forms include:

• Braided Weave: Uses eight spindles on two tracks, forming a square cross-section without a core. It offers compensation for shaft vibration and eccentricity but is prone to rough surface patterns and loose structure when the cross-section is large.

• Layered Weave: Woven with 8 to 60 spindles based on size requirements, typically 1–4 layers, without a core. It is dense and provides strong sealing but prone to delamination due to the lack of fiber bonding between layers, thus suited for static seals or low-speed equipment.

• Sandwich Weave: Consists of rubber or metal as the core and fibers woven in multiple outer layers. It is strong, flexible, and well-sealed but similar to layered weave, where surface wear may cause delamination. Commonly used in pumps and valves, rarely in reciprocating devices.

• Heart-Core Weave: Woven on three or four tracks using 8 to 60 spindles, resulting in a square cross-section with a smooth surface, high elasticity, wear resistance, and tight sealing. This structure maintains integrity even after surface wear and offers long service life, making it an advanced weaving method.

When selecting a packing gland, the weaving type should be chosen based on specific working conditions to maximize its sealing performance.

4. Classification, Composition, and Application of Packing Glands
Due to varying working conditions, packing glands come in many types. For better classification and selection, they are commonly grouped based on the primary sealing material:

1. Natural Fiber Packing: Made from natural cotton, hemp, wool, etc.

2. Mineral Fiber Packing: Mainly asbestos-based materials.

3. Synthetic Fiber Packing: Includes graphite, carbon fiber, PTFE, Kevlar, acrylic-silicone composite fiber, etc.

4. Ceramic and Metallic Fiber Packing: Includes silicon carbide, boron carbide, and alkali glass fiber-based materials.

Single-fiber materials often have inherent limitations such as porosity or poor lubricity, which can lead to leakage or high friction. To enhance sealing density and lubrication, additives such as lubricants and fillers are used—like mineral oil mixed with graphite powder, molybdenum disulfide grease, talcum powder, mica, glycerin, vegetable oil, or PTFE dispersion with surfactants. Special additives like zinc particles, inhibitors, and molybdenum-based corrosion inhibitors are also applied to reduce equipment wear.

With advancements in science and technology, nanotechnology has played an increasingly important role in the sealing industry. It helps uncover inherent material characteristics and compensate for their shortcomings while enhancing desirable properties. Through collaboration with leading domestic and international nano research institutes, nano-packing series have been successfully developed, patented, and brought to market. This has significantly improved sealing performance and service life, opening new frontiers for packing applications and bringing considerable economic benefits to users.