Common sense of the hottest mechanical seals

2022-08-15
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Common sense of mechanical seals

mechanical seals are one of the basic mechanical components with precision and complex structure. They are the key components of various pumps, reaction reactors, turbine compressors, submersible motors and other equipment. Its sealing performance and service life depend on many factors, such as type selection, machine accuracy, correct installation and use, etc

I. selection method

mechanical seals have high temperature and low temperature resistance mechanical seals, high pressure and corrosion resistance mechanical seals, particle medium resistance mechanical seals and mechanical seals suitable for vaporizing light hydrocarbon media according to different working conditions and media properties. Mechanical seals with different structural types and materials should be selected according to different uses

the main parameters of model selection include: seal cavity pressure (MPA), fluid temperature (℃), working speed (m/s), fluid characteristics and effective space for installing seals

the basic principle of model selection is:

1 According to the pressure of the seal cavity, the seal structure is determined to be balanced or unbalanced, single face or double face, etc

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 systems such as lubrication, flushing, heat preservation, cooling, etc

4. According to the effective space for installing the seal, it is determined to use multi spring, single spring or wave spring, internal or external

II. Installation and use requirements of mechanical seal

1 The requirements of mechanical seal on machine accuracy (taking pump mechanical seal as an example)

at the same time, it provides parts with excellent quality (1) the radial runout tolerance of the shaft (or shaft sleeve) where the mechanical seal is installed shall not exceed 0.04 ~ 0.06mm at most

(2) the axial movement of the rotor shall not exceed 0.3mm

(3) the maximum runout tolerance of the positioning end face of the seal cavity combined with the seal end cover to the shaft (or shaft sleeve) surface shall not exceed 0.04 ~ 0.06mm

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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 there is no electromagnetic interference and whether the number of parts is complete

(3) for mechanical seals with parallel coil spring drive, the spring can be divided into left and right rotation, which must be selected according to the rotation direction of the rotating shaft

3. Installation

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

(1) determination of installation size

during installation, the installation size of mechanical seal should be ensured according to the product instructions or samples

(2) before installation, the shaft (shaft sleeve) and gland should be free of burrs, and the bearing should be in good condition; Seals, shafts, seal cavities, and glands should be cleaned. In order to reduce friction resistance, the part of the shaft where the mechanical seal is installed should be thinly coated with oil for lubrication. Considering the compatibility of the rubber O-ring, if oil is not suitable, soapy water can be coated. The floating stationary ring does not have the structure of anti rotation pin, so it should not be oiled, and it should be dry installed into the gland

(3) first install the stationary ring and the gland on the shaft, be 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 tightened evenly several times

before fixing the gland, manually push the compensation ring 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 transmission medium is too high, too low, or contains impurity particles, flammable, explosive, toxic, corresponding measures such as blocking, washing, cooling, and filtering must be taken, which can be applied to a variety of environments and different occasions

(2) turn by hand before operation, and pay attention to whether the torque is too large, whether there is friction and abnormal sound

(3) pay attention to the rotation direction, whether the coupling is centered, whether the lubricating oil addition at the bearing is appropriate, and whether the piping is correct

(4) before operation, first open the medium and cooling water valves, and check whether the gas in the sealing chamber is completely discharged to prevent leakage caused by static pressure, and then start the machine for operation

(5) whether the work is normal and stable after driving, whether there is abnormal torque, abnormal sound and overheating caused by shaft rotation

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