Formula for calculating packing length and method of packing installation

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Formula for calculating the length of packing material, and formula for determining the required length of packing material when installing it: (shaft diameter d + packing width) × 1.07 × 3.14. Formula for calculating the cross-sectional area of the packing material: (diameter of the stuffing box – diameter of the valve stem) / 2. Principles for selecting packing material: prefer larger sizes over smaller ones, and tighter fit over looser one! Method of installing packing: The effective sealing of pumps and valves depends on the overall condition of all components. It is particularly important to ensure that, before installing the packing, the equipment that requires replacement has been properly isolated from the site and the system. The following information is intended to guide maintenance personnel, engineers, and assemblers in properly installing and adjusting the packing. 1. Tools required: Special tools are needed to remove the old packing and replace it with new one, as well as a tensioner to pre-tighten the gland nut. In addition, standard safety facilities must be used regularly, and relevant safety regulations must be followed. Before installation, it is first necessary to become familiar with the following equipment: a cutter for trimming the packing rings, a torque wrench or screwdriver for checking torque, safety helmets, inner and outer calipers, lubricant for fasteners, mirrors, a packing remover, tools for cutting the packing, vernier calipers, etc. 2. Cleaning and inspection 1) Slowly loosen the gland nut of the stuffing box to release any residual pressure within the packing assembly ； 2) Remove all old packing and thoroughly clean the shaft/rod stuffing box ； 3) Check the shaft/rod for corrosion, dents, scratches, or excessive wear ； 4) Check other parts for burrs, cracks, or wear, as they can reduce the lifespan of the packing ； 5) Check whether there is an excessive gap in the stuffing box, as well as the degree of eccentricity of the shaft/rod ； 6) Replace components with significant defects ； 7) Inspect the old packing to serve as a basis for failure analysis, in order to identify the causes of early packing failure. 3. Measurement and recording: Record the diameter of the shaft/rod, as well as the diameter and depth of the stuffing box. When a water seal ring is used, record the distance from the bottom to the top of the stuffing box. 4. Selecting the gasket: 1) Ensure that the selected gasket meets the operating conditions required by the system and equipment ； 2) Based on the measurement records, calculate the cross-sectional area of the packing and the number of packing rings required ； 3) Inspect the packing to ensure it is free of defects ； 4) Before installation, ensure that the equipment and gaskets are clean. 5. Preparation of the packing ring 1) Winding the packing: Wind the packing around a shaft of appropriate size, or use a calibrated packing ring cutting machine ； As required, cut the packing neatly into butt (square) or oblique (30-45 degrees) joints, cutting one ring at a time, and use the shaft or valve stem to check whether the dimensions are appropriate. 2) Molded packing – Ensure that the dimensions of the ring match those of the shaft or valve stem precisely; if necessary, cut the packing ring in accordance with the manufacturer’s instructions or requirements. 6. Installing the packing: Carefully install one packing ring at a time, winding each ring around the shaft or valve stem. Before installing the next ring, ensure that the current ring is fully in place within the stuffing box; the next ring should be positioned at an angle to the previous one, with at least a 90-degree gap, and ideally 120 degrees. After the topmost ring is installed, tighten the nut by hand and press the cover down evenly. If there is a water seal ring, check whether its distance from the top of the stuffing box is correct. At the same time, ensure that the shaft or valve stem can rotate freely. 7. Adjusting the packing 1) Packing for pumps (1) Continue to tighten the gland nut by hand ； (2) After starting the pump, adjust the gland nut; a slight amount of leakage is acceptable at this stage ； (3) Slowly tighten the gland nut to gradually reduce the leakage until it reaches an acceptable level ； (4) If the leakage stops suddenly, the gland nut should be tightened again to re-adjust and prevent the packing from overheating ； (5) Adjust the leakage rate until it reaches a stable state. 2) Gasket for valves: Consult the gasket manufacturer or the technical department of the company regarding the specified torque or compression percentage. Tighten the gland nut following these steps: (1) Apply torque to the gland nut at 30% of the full torque value, or according to the specified compression percentage; (2) Open and close the valve several times, and once the valve is in the closed position, apply the full torque ； (3) Repeat step (2) 3 or 4 times. 8. Re-tightening and replacement: After several hours of operation, check the adjustment of the gland; tighten it if necessary. When the gland can no longer be adjusted further, the packing must be replaced.