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Mechanical seal common sense
- Aug 07, 2018 -

Mechanical seals are one of the basic mechanical components with precise and complicated structure. They are the key components of various pumps, reaction synthesis kettles, turbine compressors, submersible motors and other equipment. Its sealing performance and service life depend on many factors, such as selection, machine accuracy, proper installation and use.


First, the mechanical seal installation and use requirements

1. Mechanical seal requirements for machine accuracy (taking pump mechanical seal as an example)

(1) The radial runout tolerance of the shaft (or bushing) on which the mechanical seal is installed shall not exceed 0.04 to 0.06 mm.

(2) The axial movement of the rotor does not exceed 0.3 mm.

(3) The locating tolerance of the positioning end face of the sealing cavity combined with the sealing end cap to the shaft (or bushing) surface shall not exceed 0.04~0.06mm.

2. Confirmation of seals

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

(2) Before installation, carefully compare with the assembly drawing, and the number of parts is complete.

(3) The mechanical seal adopting the parallel spring transmission, the spring has the left and right rotation points, and must be selected according to the rotation direction of the rotating shaft.

Second, the selection method

Mechanical seals according to different working conditions and medium properties, high temperature resistant, low temperature resistant mechanical seals, high pressure resistant, corrosion resistant mechanical seals, mechanical seals resistant to particulate media, and mechanical seals for light hydrocarbon media that are easy to vaporize, etc. The use of mechanical seals for different structural types and materials.

The main parameters of the selection are: sealed chamber pressure (MPa), fluid temperature (°C), working speed (m/s), fluid characteristics and effective space for sealing. The basic principles of selection are:

1. According to the pressure of the sealed cavity, it is determined that the sealing structure adopts balanced or unbalanced type, single end or double end.

2. According to the working speed, it is determined to adopt rotary or static type, fluid dynamic pressure type or non-contact type.

3. According to the temperature and fluid properties, determine the friction pair and auxiliary sealing materials, and correctly select the mechanical seal cycle protection system such as lubrication, flushing, heat preservation and cooling.

4. According to the effective space for installing the seal, it is determined to use a multi-spring or single spring or wave spring, built-in or exterior.

Third, the installation

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

(1) Determination of installation size

When installing, the installation dimensions of the mechanical seal should be guaranteed according to the product's instruction manual and samples.

(2) Before loading, the shaft (sleeve sleeve) and gland should be free of burrs and the bearing condition is good; the seal, shaft, seal chamber and gland should be cleaned. In order to reduce the frictional resistance, the mechanical seal on the shaft should be thinly coated with a layer of oil for lubrication. Considering the compatibility of the rubber O-ring, if it is not suitable for oil, it can be coated with soapy water. The floating static ring does not have an anti-rotation structure. Do not apply oil. Dry gland should be installed.

(3) First install the static ring and the gland on the shaft, taking care not to touch the shaft, and then load the east ring assembly. The set screws of the spring seat or the drive base should be tightened evenly several times.

Before the gland is fixed, the compensating ring is manually pressed for axial compression. After the loosening, the compensating ring can automatically spring back without jamming, and then the gland bolt is evenly locked.

4. Use

(1) When the temperature of the conveying medium is too high, too low, or contains impurity particles, flammable, explosive, and toxic, it is necessary to take corresponding measures such as blocking, rinsing, cooling, and filtering.

(2) Use the hand-cranked car before the operation, pay attention to whether the torque is too large, whether there is any rubbing or abnormal sound.

(3) Pay attention to the direction of rotation, whether the coupling is centered, whether the lubrication of the bearing part is appropriate, and whether the piping is correct.

(4) Before the operation, first open the medium and cooling water valves, check whether the gas in the sealed chamber is completely eliminated, prevent the static pressure from causing leakage, and then start the operation.

(5) Whether the work is normal and stable after starting, whether there is abnormal torque caused by shaft rotation, abnormal noise and overheating.