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Principle and installation of sealing packings: After the packing is inserted into the sealing chamber, it is axially compressed by the gland. Due to the plasticity of the packing, a radial force is generated, allowing it to make tight contact with the smooth shaft. At the same time, the lubricant impregnated in the PTFE packing is squeezed out, forming an oil film between the contact surfaces. Since the contact condition is not particularly uniform, boundary lubrication occurs at the contact areas, similar to that in sliding bearings; hence this is referred to as the bearing effect. The uncontacted recesses form small oil grooves with thicker oil films. When there is relative movement between the shaft and the packing, the contact areas and the non-contact areas together create an irregular labyrinth that prevents the leakage of liquid – this is known as the labyrinth effect. The gland applies axial pressure on the sealing packing through a compression sleeve, causing the sealing PTFE packing to deform axially and radially; thus, the gap in the sealing chamber is filled, achieving sealing. Using it can extend the lifespan of seals, reduce maintenance costs, and lower pollution levels. The dual-seal design achieves zero-leakage performance; it can withstand radial loads in both directions and ensures sealing in both directions. This seal is primarily used in fluid transfer systems, including various medical and dental devices. With over 60 years of experience in seal production, American company Minnesota Rubber & Plastics can provide customized design for two-way seals. To achieve zero leakage, Minnesota Rubber & Plastics designed a special double-lip seal, with one sealing lip subjected to pressure in the positive direction and the other to pressure in the opposite direction. Under pressure, the sealing lip of this seal can press tightly against the sealing surface to prevent liquid leakage. Seal size is also an important factor in double-lip seal applications. Smaller seals can reduce the likelihood of leaks. I. What are the precautions before installing the sealing packing? Precautions before installing the sealing packing: Removing the old packing and checking the packing box are key steps in the preliminary installation preparations. Before installing new packing, remove all the old packing using specialized tools, and clean the packing box thoroughly. Check all parts of the packing box for any damage or eccentricity; damaged valve stems, shaft sleeves, and packing boxes can all affect the performance of the packing. Check whether other components can still be used. Replace all damaged parts. II. How to choose the right packing? How to choose the right packing? Two things must be taken into consideration when selecting packing. ①The operating conditions must be compatible with the performance of the packing. The most suitable packing can be selected based on relevant technical data. ②The size of the packing must be selected correctly based on the sealing requirements. To determine the cross-sectional area, use the following formula: Cross-sectional area = (diameter of the stuffing box – diameter of the valve stem) / 2. Devices that are damaged may require a gasket with a slightly larger cross-sectional area in order to compensate for the damage. III. Details to Note for Cutting and Installing Sealing Packing Details to note for cutting and installing sealing packing: 1. Select the appropriate packing, and use cutting equipment to precisely cut the packing ring to the desired length. If no such cutting equipment is available, the length of the packing can be calculated using the formula L = (shaft diameter D + packing width S) × 1.07 × √2. For rotating shafts, a 90° cut is generally used, while for valves, a 45° cut is employed. Never try to determine the length using the tightly wound packing box. Or wrap the packing around the same as the valve stem. On one of the tubes, press it tightly, but do not stretch the gasket. It is then cut into sample rings, and checked to ensure that it can properly fill the space and that there are no gaps at its joints. Then, the sample ring can be used as a standard to cut other packing rings. If these finished products are created on a flat surface, and if the packing is soft or prone to deformation, a small strip can be made based on the sample ring, and then the remaining packing rings can be fabricated using rope. 2. When the packing is used in valves, its cross-section should match the space available in the valve; it is advisable to use a pre-compression ring. When used in pumps, the cross-section of the packing and the space available in the valve (around 0.3 MM–0.6 MM) create a leakage gap between the shaft and the packing, which facilitates lubrication and heat dissipation. 3. Install one packing ring at a time, making sure that no dust or other debris is stuck to each packing. If necessary, the packing ring should be lubricated with the same clean lubricating oil used on the valve stem. Install each packing ring at 90° to the adjacent ones. The ring is slowly pulled apart axially.