Various guidelines for mechanical seal life1

Various guidelines for mechanical seal life

21/11/01 09:46:11

Because the life of mechanical seals can be directly related to the performance and efficiency of equipment, we need to introduce and understand the various criteria for the life of its accessories.

As we all know, mechanical seals are one of the basic mechanical components with precise, dense and complex structure, and are the key components of various pumps, reaction synthesis kettles, turbo compressors, submersible motors and other equipment. Its sealing performance and service life depend on many factors, such as model selection, machine accuracy, correct installation and use, etc.

1. Selection method

According to different working conditions and medium properties, there are high temperature resistant, low temperature resistant seals, high pressure resistant, corrosion resistant seals, particle medium resistant seals and seals suitable for light hydrocarbon medium that is easy to vaporize, etc., and should be used according to different purposes. Choose seals of different construction types and materials.

The main parameters of the selection are: sealing cavity pressure (MPA), fluid temperature (℃), working speed (M/S), fluid characteristics and effective space for installation and sealing, etc.

The basic principles of model selection are:

1: According to the pressure of the sealing cavity, determine whether the sealing structure is balanced or unbalanced, single-end or double-end, etc.

2: According to the working speed, determine whether to use rotary or static, hydrodynamic or non-contact.

3: According to the temperature and fluid properties, determine the friction pair and auxiliary sealing materials, and correctly select the lubrication, flushing, heat preservation, cooling and other seal circulation protection systems.

4: According to the effective space of the installation seal, it is determined to use multiple springs or single springs or wave springs, built-in or external.

2. Installation and use requirements

1: Requirements for machine accuracy (take pump as an example)

(1) The radial runout tolerance of the shaft (or bushing) where the seal is installed shall not exceed 0:04~0:06MM.

(2) The axial movement of the rotor does not exceed 0:3MM.

(3) The runout tolerance of the positioning end of the sealing cavity combined with the sealing end cover facing the surface of the shaft (or shaft sleeve) shall not exceed 0:04~0:06MM.

2: Confirmation of seals

(1) Confirm whether the installed seal is consistent with the required model.

(2) Before installation, carefully check with the general assembly drawing to see if the number of parts is complete.

(3) For mechanical seals driven by parallel springs, the springs are divided into left and right rotations, which must be selected according to the rotation direction of the rotating shaft.

3: The installation method varies with the type of seal and the type of machine, but the installation essentials are almost the same. The installation steps and precautions are as follows:

(1) When installing the mechanical seal, the installation size should be guaranteed according to the product instruction manual or sample.

(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 cleaned. In order to reduce frictional resistance, the parts where the seals are installed on the shaft should be coated with a thin layer of oil for lubrication. Considering the compatibility of rubber O-rings, if oil is not suitable, soapy water can be applied. The structure of 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, being careful 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.

(4) 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: Use

(1) When the temperature of the conveying medium is too high, too low, or contains impurity particles, flammable, explosive or toxic, corresponding measures such as blocking, flushing, cooling, and filtration must be taken.

(2) Turn the car by hand before running, pay attention to whether the torque is too large, whether there is friction and 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 correct.

(4) Before operation, first open the medium and cooling water valves, check whether the gas in the sealed cavity is fully discharged, and prevent 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 the rotation of the shaft, as well as abnormal noise and overheating.