Mechanical seal is one of the mechanical basic components with precise and complex structure, and is the key component of various pumps, reaction synthesis kettle, turbine compressor, submersible motor and other equipment. Its sealing performance and service life depend on many factors, such as model selection, machine precision, correct installation and use.
 
  Firstly,selection method of mechanical seal according to the working conditions and the properties of medium, there are high temperature resistant, resistant to low temperature mechanical seal, mechanical seal, high pressure resistance and corrosion resistance of granules medium mechanical seal and adapt easy vaporization of the mechanical seal of light hydrocarbon medium, etc., should be according to the different use to select different structural type and materials of mechanical seal. The main parameters of selection include: sealing chamber pressure (MPA), fluid temperature (℃), working speed (M/S), fluid characteristics and effective space for installation and sealing. What is the general knowledge of mechanical seals? The basic principles of selection are:
1, according to the pressure of the sealing cavity, determine the sealing structure to be balanced or non-balanced, single end or double end.
2, according to the working speed, determine the use of rotary or static, fluid dynamic pressure or non-contact type.
3, according to the temperature and fluid properties, determine the friction pair and auxiliary sealing materials, and the correct choice of lubrication, washing, heat preservation, cooling and other mechanical seal cycle protection system.
4, according to the effective space for installation and sealing, determine the use of multiple springs or single spring or waveform spring, inside or outside.
 
  Second, the installation and use of mechanical seals require common sense of mechanical seals
  1. Requirements for machine precision of mechanical seal (take mechanical seal for pump as an example)
(1) the radial runout tolerance of the shaft (or shaft sleeve) at the installation of mechanical sealing position is not more than 0.04 ~ 0.06MM.
(2) axial movement of the rotor shall not exceed 0.3mm.
(3) the run-out tolerance of the positioning end facing the shaft (or shaft sleeve) surface combined with the sealing cavity and the sealing end cover is not more than 0.04 ~ 0.06MM. General knowledge of mechanical seals
  2. Seal confirmation
(1) confirm that the seal installed is consistent with the required type.
(2) before installation, please carefully check with the final assembly drawing to see whether the number of parts is complete.
(3) the use of parallel coil spring drive mechanical seal, the spring can be left, right, according to the rotation axis of the choice.
  3. Installation and installation methods vary with the types of mechanical seals and machines, but the installation essentials are almost the same. Installation steps and precautions are as follows:
(1) the installation size shall be determined according to the product instruction manual or sample to ensure the installation size of the mechanical seal.
(2) before loading, the shaft (shaft sleeve) and gland shall be free of burr and the bearing shall be in good condition; Seals, shafts, sealing cavities and gland should be cleaned. To reduce friction resistance, the installation of mechanical seal shaft parts to thin layer of oil, in order to lubricate, considering the rubber O ring compatibility, if not suitable for oil, can be coated with soapy water. Floating static ring without anti - pin structure, should not be oiled, dry type loading gland.
(3) first install the static ring and the gland on the shaft, pay attention not to touch the shaft, and then install the moving ring assembly. The set screw of spring seat or drive seat should be tightened evenly several times. Before the gland is fixed, push the compensation ring by hand for axial compression. After releasing the compensation ring, it can automatically spring back without stagnation, and then lock the gland screw evenly.
  4, the use of
(1) when the transmission medium temperature is too high, too low, or contains impurities particles, flammable, explosive, toxic, take the corresponding measures of blocking, washing, cooling, filtering.
(2) turn the car by hand before operation, and pay attention to whether the torque is too large, whether there is any rubbing or abnormal sound.
(3) pay attention to the rotation, whether the coupling is aligned, whether the lubricating oil addition of the bearing part is appropriate, whether the piping is correct.
(4) before operation, firstly open the valve of medium and cooling water, check whether all the gas in the sealing chamber is discharged to prevent static pressure from causing leakage, and then start the operation.
(5) after starting, whether the work is normal and stable, there is no abnormal torque caused by shaft rotation, abnormal sound and overheating.

2019-08-09

What is the general knowledge of mechanical seal selection?

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