Selection requirements for mechanical seals

News | 2019-05-31 14:12

Mechanical seals belong to one of the basic mechanical components with precise and complicated structure, and 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, correct installation and use.
I. Selection method:
The main parameters of mechanical seal selection: pressure of the seal cavity (MPA), fluid temperature (° C), working speed (M / S), characteristics of the fluid, and effective space for installing the seal.
According to different working conditions and media properties, mechanical seals have high temperature and low temperature resistance mechanical seals, high pressure and corrosion resistance mechanical seals , granular media resistance mechanical seals , and mechanical seals adapted to light hydrocarbon media that are easily vaporized.
Seals, etc., should be selected according to different uses of different structural types and mechanical seals.
The basic principles of selection are:
1: According to the pressure of the sealed cavity, determine whether the sealing structure is balanced or unbalanced, single or double end, 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 system such as lubrication, flushing, heat preservation, cooling, etc.
4: According to the effective space of the installation seal, it is determined to use multiple springs or single springs or wave springs, internal or external.
Requirements for installation and use of mechanical seals:
1: Mechanical seal requirements for machine accuracy (Take mechanical seal for pump as an example)
(1) The maximum radial runout tolerance of the shaft (or sleeve) where the mechanical seal is installed is not more than 0: 04 ~ 0: 06MM.
(2) The axial movement of the rotor does not exceed 0: 3MM.
(3) The maximum run-out tolerance of the positioning end surface of the sealed cavity and the sealed end cap to the surface of the shaft (or sleeve) does not exceed 0:04 to 0: 06MM.
2: Confirmation of seals (1) Confirm whether the installed seal is consistent with the required model.
(2) Before installation, carefully compare with the assembly drawing, and check whether the number of parts is complete.
(3) The mechanical seal adopts parallel coil spring transmission. The springs are divided into left and right rotations, 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 the installation methods are almost the same. The installation steps and precautions are as follows:
(1) Determination of installation size When installing, the installation size of the mechanical seal should be guaranteed according to the product instruction manual or sample.
(2) Before installation, the shaft (shaft sleeve) and gland should be free of burrs and the bearing should be in good condition; the seals, shaft, seal cavity and gland should be cleaned.
In order to reduce frictional resistance, the part where the mechanical seal is 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, soap water can be applied.
The floating static ring does not have anti-rotation pin structure. It is not suitable for oiling, and it should be installed dry in the gland.
(3) First install the static ring and gland on the shaft, taking care not to touch the shaft, and then install the moving ring assembly. The set screws of the spring seat or transmission seat should be evenly tightened in several times.
Before the gland is not fixed, the compensation ring is pushed by hand for axial compression. After being released, the compensation ring can automatically spring back without jamming, and then the gland bolts are evenly locked.
4: Use (1) When the temperature of the conveying medium is too high, too low, or contains foreign particles, flammable, explosive, and toxic, corresponding blocking, washing, cooling, filtering and other measures must be taken.
(2) Turn the car by hand before running, pay attention to whether the torque is too large, whether there is rubbing and abnormal sound.
(3) Pay attention to the direction of rotation, whether the coupling is centered, whether the addition of lubricating oil at the bearing part is appropriate, and whether the piping is correct.
(4) Whether the work is normal and stable after driving, whether there is abnormal torque caused by shaft rotation, and abnormal noise and overheating.
(5) Before operation, first open the medium and cooling water valves, check whether the gas in the sealed cavity is completely exhausted to prevent leakage caused by static pressure, and then start up.