Knowledge of mechanical seals

Knowledge of mechanical seals Mechanical seals are classified as one of the basic mechanical components with fine and messy structure. They are the key components of various pumps, reaction kettles, turbo compressors, submersible motors and other equipment. Its sealing function and service life depend on many factors, such as type selection, machine accuracy, and accurate installation and application of Grundfos mechanical seals. 1. Requirements for the installation and use of mechanical seals 1. The requirements of mechanical seals for machine accuracy (take mechanical seals for pumps as an example) (1) The shaft (or sleeve) of the imported mechanical seal at the location where the mechanical seal is installed has the largest radial runout tolerance Does not exceed 0.04～0.06mm. (2) The axial movement of the rotor does not exceed 0.3mm. (3) The positioning end of the sealing cavity and the sealing end cover faces the outer surface of the shaft (or sleeve). The maximum runout tolerance of the cartridge mechanical seal does not exceed 0.04～0.06mm. 2. Recognition of seals (1) Acknowledge whether the installed seal is consistent with the required type. (2) Check carefully with the final assembly drawing before installation to see if the number of parts is complete. (3) Choose a mechanical seal driven by a parallel tension spring. The tension spring can be divided into left and right rotation, which must be selected according to the rotation history of the shaft. 2. Selection method Mechanical seals are different according to working conditions and media properties. There are high temperature and low temperature resistant mechanical seals, high pressure resistant and corrosion resistant mechanical seals, particle resistant mechanical seals and mechanical seals that are accustomed to easy vaporization of light hydrocarbon media. For seals, mechanical seals with different construction types and materials should be selected based on different uses. The main parameters of the selection are: the pressure of the sealed cavity (MPa), the fluid temperature (℃), the working speed (m/s), the characteristics of the fluid, and the useful space for installing the seal. The basic principles of the selection are: 1. According to the pressure of the sealed cavity, determine whether the sealing structure is balanced or unbalanced, single end face or double end face, etc. 2. According to the working speed, determine the choice of rotating type or stop type, fluid dynamic pressure type or non-touch type. 3. According to the temperature and fluid properties, determine the conflict pair and auxiliary sealing data, and accurately select the smooth, scouring, heat preservation, cooling and other mechanical seal circulation protection systems. 4. According to the useful space for installation and sealing, determine the choice of multiple springs or single springs or wave springs, built-in or exterior-mounted. 3. Installation methods vary with mechanical seal types and machine types, but the installation methods are almost the same. The installation process and precautions are as follows: (1) The installation size is determined and the installation should be based on the product. Use instructions or samples to ensure the installation dimensions of the mechanical seal. (2) Before installation, the shaft (sleeve) and gland should be free of burrs, and the bearing should be in good condition; the seals, shaft, seal cavity, and gland should be cleaned. In order to reduce the conflict resistance, the part where the mechanical seal is installed on the shaft should be coated with a thin layer of oil for smoothness. Taking into account the compatibility of the rubber O-ring, if it is not suitable to use oil, it can be coated with soapy water. Floating static ring has no anti-rotation pin structure, so it is not suitable to be oiled and should be dry installed in the gland. (3) Install the static ring and gland on the shaft first, taking care not to collide with the shaft, and then install the moving ring assembly. The tightening screws of the spring seat or transmission seat should be evenly tightened in several rounds. Before the gland is fixed, push the compensation ring by hand to axially tighten it. After loosening the compensation ring, the compensation ring can actively spring back to the appearance of no jamming, and then the gland bolts are evenly locked. 4. Application (1) When the temperature of the conveying medium is too high, too low, or rich in impurity particles, flammable, explosive, or toxic, it is necessary to adopt corresponding measures such as blocking, scouring, cooling, and filtering. (2) Before operation, turn the car by hand, pay attention to whether the torque is too large, whether there is rubbing or abnormal sound. (3) Pay attention to the direction of rotation, whether the coupling is centered, whether the smooth oil addition at the bearing part is appropriate, and whether the piping is accurate. (4) Open the medium and cooling water valve before operation, check whether the gas in the sealed cavity is completely discharged to avoid leakage caused by static pressure, and then start the operation. (5) Whether the work is normal and stable after driving, whether there is abnormal torque caused by shaft rolling, abnormal noise and overheating appearance. Keywords: Grundfos mechanical seal, imported mechanical seal, cartridge mechanical seal