Common sense and application of mechanical seal selection

Mechanical seals are one of the most sophisticated and complex mechanical basic components, and are key components of various pumps, reaction components, turbocompressors, submersible motor mechanical seals and other equipment. Its sealing function and service life depend on many factors, such as model selection, machine accuracy, and accurate device use.

1. Selection method The mechanical seals are different according to the operating conditions and the properties of the medium mechanical seals. There are high temperature and low temperature mechanical seals, high pressure and corrosion resistance mechanical seals, particle medium mechanical seals and light hydrocarbon media that are easy to vaporize. Mechanical seals, etc., should be selected according to different uses of mechanical seals with different structural types and materials. The main parameters for selection are: sealed cavity pressure (MPA), fluid temperature (°C), operating speed (M/S), fluid characteristics, and useful space for device sealing. The basic principles of selection are: 1. According to the pressure of the sealing cavity, it is determined that the sealing structure should be balanced or unbalanced, single-end or double-end, etc. 2. According to the working speed, it is determined to choose the rotary type or the stop type, the fluid dynamic pressure type or the non-touch type. 3. According to the temperature and fluid properties, determine the conflicting pair and auxiliary sealing materials, and accurately select the mechanical seal cycle maintenance system such as lubrication, erosion, heat preservation, and cooling. 4. According to the effective space sealed by the device, it is determined to choose multiple springs or single springs or wave springs, built-in or external.

2. Installation and application requirements of mechanical seals 1. The requirements of mechanical seals for machine accuracy (taking pump mechanical seals as an example) (1) The radial runout of the shaft (or shaft sleeve) at the mechanical seal part of the device should not exceed the maximum 0.04～0.06MM. (2) The axial movement of the rotor does not exceed 0.3MM. (3) The runout of the positioning end of the sealing cavity and the sealing end cover facing the surface of the shaft (or shaft sleeve) should not exceed 0.04~0.06MM at most. 2. Confirmation of seals (1) Confirm whether the installed seal is the same as the requested type. (2) Before installation, carefully check with the general assembly drawing to see if the number of parts is complete. (3) The mechanical seal driven by the parallel spring is selected, and the spring has left and right rotation, which must be selected according to the rotation history of the rotating shaft. 3. The installation method varies with the type of mechanical seal and the variety of the machine, but the installation method is almost the same. The installation steps and precautions are as follows: (1) When determining the installation size, it should be installed according to the product. Use instructions or samples to ensure the size of the mechanical seal. (2) Before loading, the shaft (sleeve) and gland should be free of burrs, and the bearing should be in good condition; the seals, shaft, sealing cavity and gland should be clean. 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. Considering the compatibility of the rubber O-ring, if oil is not suitable, soapy water can be applied. The structure of the floating static ring without anti-rotation pin should not be oiled, and should be installed in the gland dry. (3) Install the static ring together with the gland on the shaft first, taking care not to collide with the shaft, and then install the moving ring assembly. The set screw of the spring seat or transmission seat should be evenly tightened several times. Before the gland is not fixed, push the compensation ring by hand for axial compression. After loosening, the compensation ring can automatically spring back without jamming, and then lock the gland bolts evenly. 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 take corresponding measures such as blocking, flushing, cooling and filtering. (2) Turn the car by hand before operation, and pay attention to whether the torque is too large, whether there is friction or abnormal sound. (3) Pay attention to the direction of rotation, whether the coupling is centered, whether the addition of lubricating oil in the bearing part is appropriate, and whether the piping is accurate. (4) Before the operation, first open the medium and cooling water valves to check whether the gas in the sealed cavity is completely discharged, so as to avoid leakage caused by static pressure, and then start the operation. (5) Is the operation normal and stable after driving, whether there is abnormal torque caused by shaft rotation, abnormal noise and overheating phenomenon.