Mechanical seals are widely used for various types of pumps. The mechanical seal is a high precision sealing device, which has certain requirements for the installation and use conditions.
1. General principles for installation and use of mechanical seals
(1) To understand the condition of the equipment, it is necessary to understand the rotational speed and shaft diameter of the shaft of the equipment; the precision of the equipment manufacturing and the size of the sealed chamber; the service life of the equipment itself and the status of the equipment in the production process.
(2) Estimate media pressure. The pressure in the seal chamber of the pump is generally not the outlet pressure of the pump but is lower than the outlet pressure of the pump.
(3) Find out the condition of the sealed medium. To understand the state of the sealed medium, whether it is gaseous or liquid, whether the medium contains particles and particles; understand the nature of the medium, temperature, in order to properly select the type and take the necessary cooling, flushing, lubrication measures.
2. Technical requirements for installation of mechanical seals
(1) The radial runout tolerance of the shaft or bushing where the mechanical seal is installed: Ф10~50mm 0.04mm, larger than Ф50~120mm, 0.06mm. The surface roughness of the shaft or bushing should meet the technical requirements and the outer diameter dimension tolerance is h6.
(2) The axial turbulence of the drive shaft does not exceed 0.2 mm.
(3) Runout tolerance of the face of the seal cavity facing the shaft surface: Runout tolerance of the shaft or bush outer diameter face runout: Ф10~50mm, 0.04mm, greater than Ф50~120mm, 0.06mm
(4) The end face of the shaft or sleeve and the end face of the sealed cavity must be chamfered. The shaft diameter ≤ Φ30mm is 3×10°, and the shaft diameter > Φ30mm is 4×10°.
(5) When the temperature of the medium to be transported is too high, too low or contains foreign particles, flammable, explosive, and toxic, corresponding measures such as sealing, washing, cooling, and filtering should be taken.
(6) For some mechanical transmissions driven by springs, attention must be paid to the rotation of the springs, that is, the direction of rotation of the shaft should make the springs more and more tight. Otherwise, the sealing failure will be caused. The selection of the spring rotation direction is determined by the following method: Looking at the ring, the shaft rotates clockwise with a right-handed spring, and vice versa.
3, mechanical seal installation method
Mechanical seal components are very strict in terms of manufacturing accuracy or installation accuracy. If they are improperly installed, they will affect the life and sealing performance of the seal. In severe cases, the seal will quickly fail.
(1) Pre-installation work and installation precautions 1 Check that the model and specification of the mechanical seal to be installed are correct and the parts are missing.
2 Check whether the components of the mechanical seal are damaged. In particular, whether the sealing surfaces of the moving ring and the stationary ring are damaged. If damage is found, repair or replacement of new parts is required. The sealing elements need to be cleaned with gasoline or kerosene to keep the surface of all components free from dust and foreign matter.
The surface of the shaft or the shaft sleeve, the inner wall of the seal chamber, and the inner surface of the seal end cap have burrs or grooves or the like. If burrs or groove marks are found, they should be smoothed and polished, and cleaned with gasoline or kerosene. Keep them clean and free from dust and debris on the surface.
4 Do not use an unclean cloth or cotton gauze to clean the surfaces of the moving ring and the stationary ring. Use a clean, soft gauze, absorbent cotton, or the like.
5 The assembly process should be kept clean to ensure that the sealing surfaces of the moving ring and the stationary ring are not scratched or broken. For assembly, oil should be applied to the surface of the shaft or bushing, the cover and the sealing ring. , so as to avoid starting dry friction instantly.
(2) Assembly sequence 1 Assembly of mechanical seal stationary parts: a. Install the anti-rotation pin into the corresponding hole of the seal cap; b. Put the static ring seal on the stationary ring, and install the stationary ring into the seal cap. , pay attention to the anti-rotation pin into the static ring groove. When installing the gland, take care not to touch the shaft with the stationary ring. Bolts should be evenly tightened several times.
2 mechanical seal rotating parts assembly: The mechanical seal of the rotating parts one by one in accordance with the order of assembly to the shaft. If there is a bushing, the rotating parts of the mechanical seal are assembled to the bushing in turn, and then the shaft with the mechanical seal rotating part is fitted on the shaft.
The 3-end cap is mounted on the seal and tightened evenly with screws.
4 whether it is easy to run the test, if the disk is not moving or hard, you should check whether the assembly size is correct.
4, mechanical seal operation troubleshooting
(1) Begin leakage 1 Check whether the assembly quality meets the technical requirements and whether the spring compression is in compliance with the regulations.
2 Check if the sealing surfaces of the moving ring and the stationary ring are damaged.
3 Check that the seal face is straight.
(2) The amount of leakage during operation is suddenly too high. At this time, it is necessary to stop and inspect. 1 Check the wear condition and surface quality of the moving ring and static ring sealing end surface. If it has been damaged, it should be repaired or replaced with a new one.
2 Check that the installation position of the auxiliary ring of the ring and the stationary ring is correct (such as the lip of the V-ring should be toward the pressure end), and whether there is any damage. If it is installed incorrectly, reinstall it. If it is damaged, it should be changed again.
3 Check whether the sealed cavity is mixed with solid impurities, whether the transmission seat is filled with impurities, affect the axial floating of the moving ring and the compensation of the spring.
4 Check whether the tightening screws are loose and whether they affect the normal working state of the mechanical seal.
5 Check that the screws securing the end caps are loose and cause deflection of the sealed end caps.
6 Check whether the pump's axial turbulence and radial vibration exceed the technical requirements of use.
7 If the sleeve is installed, check whether the seal between the sleeve and the shaft is damaged and the position is correct.
8 Check whether there is seal fluid circulation in the seal body and whether the mechanical seal is in dry friction state.
