Some knowledge of O-rings and the principle of mechanical seals

  Mechanical seals for pumps are widely used in various types of pumps. Mechanical seal is a kind of high-precision sealing equipment, which has specific requirements for design and operating conditions.

1. General guidelines for the design and use of mechanical seals

(1) To know the condition of the equipment, you need to know the rotational speed and shaft diameter of the equipment shaft; design and manufacture accuracy and the size of the sealing chamber, the service life of the equipment itself, and the orientation of the equipment in the production process must be considered in a comprehensive and balanced manner.

(2) Estimated medium pressure. The seal chamber pressure of the pump is usually not the outlet pressure of the pump, but lower than the outlet pressure of the pump.

(3) Know the condition of the sealing medium. It is necessary to know the condition of the sealing medium, whether it is gaseous or liquid, whether the medium contains particles and particles; know the nature and temperature of the medium, so as to reasonably select the type and take the necessary cooling, scouring and smoothing measures.

2. Skill requirements for the use of mechanical seal equipment

(1) The radial runout tolerance of the shaft or bushing at the design mechanical seal part shall comply with Table 1. The surface roughness of the shaft or sleeve should meet the technical requirements, and the standard tolerance of the outer diameter is h6.

(2) The axial movement of the transmission shaft shall not exceed 0.2mm.

(3) The run-out tolerance of the end of the sealing chamber to the outer surface of the shaft should comply with Table 2

(4) The end face of the shaft or sleeve and the end face of the sealing cavity should be chamfered.

(5) When the temperature of the transport medium is too high, too low, or rich in impurity particles, flammable, explosive, or poisonous, corresponding isolation, flushing, cooling, filtering and other measures should be taken.

(6) For some mechanical seals driven by springs, it is necessary to pay attention to the direction of rotation of the spring, that is, the direction of rotation of the shaft should make the spring tighter and tighter, otherwise the seal will fail. The selection of the direction of rotation of the spring is determined by the following method: When the static ring is viewed from the moving ring, the shaft rotates clockwise with a right-handed spring, otherwise, a left-handed spring is used.

3. Design method of mechanical seal

Mechanical seal components are very strict in terms of manufacturing accuracy and design accuracy. If the design is not proper, it will affect the life and sealing performance of the seal, and in severe cases, the seal will fail.

Preparatory work before design and design precautions

① Check whether the type and specification of the mechanical seal to be designed are correct and whether there are any shortage of parts. ② Check whether the components of the mechanical seal are damaged, especially whether the sealing end faces of the moving ring and the static ring are damaged. If damage is found, repair or replace new parts. Each sealing element needs to be cleaned with gasoline or kerosene to keep the surface of each element free of dust and foreign matter.

③Whether there are burrs, grooves, etc. on the surface of the shaft or sleeve, the inner wall of the seal cavity, and the inner surface of the seal end cover. If burrs and grooves are found, they should be smoothed and polished, and cleaned with gasoline or kerosene, kept clean, and no dust and debris are allowed to attach to the surface.

④ Do not use unclean cloth or cotton gauze to wipe the surface of the moving ring and static ring, but clean and soft gauze, absorbent cotton and the like.

⑤ During the installation process, it should be kept clean to ensure that the sealing end faces of the moving ring and the static ring are not scratched or broken. In order to facilitate installation, oil should be applied to the surface of the shaft or sleeve, and the surface of the gland and the sealing ring during installation. Avoid dry rubbing.

order of installation

①Assembly of static parts of mechanical seal:

a. Put the anti-rotation pin into the corresponding hole of the sealing end cover;

b. Put the static ring sealing ring on the static ring, put the static ring into the sealing end cover, and pay attention to make the anti-rotation pin enter the groove of the static ring. When installing the gland, be careful not to let the static ring touch the shaft. The bolts should be tightened evenly several times.

②Mechanical seal rotating parts assembly: Assemble the rotating parts of the mechanical seal to the shaft one by one. If there is a shaft sleeve, the rotating parts of the mechanical seal must be assembled on the shaft sleeve in sequence outside, and then the shaft equipped with the rotating parts of the mechanical seal should be set on the shaft.

③ Install the end cover on the sealing body and tighten it evenly with screws.

④ Is it easy to turn the test run? If it cannot be turned or it is difficult, you should check whether the design scale is correct.

4. Troubleshooting of mechanical seal operation

1 leaked from the beginning.

① Check whether the design quality meets the requirements, and whether the spring tightening is in compliance with the regulations.

② Check whether the sealing end faces of the moving ring and the static ring are damaged.

③ Check whether the sealing end face is qualified.

2. The amount of leakage suddenly becomes too much during the operation, and the machine should be shut down for inspection at this moment

① Check the wear condition of the sealing end faces of the moving ring and the static ring and the change of the appearance quality. If damaged, repair or replace with a new one.

② Check whether the design orientation of the auxiliary sealing ring of the moving ring and the static ring is correct (for example, the lip of the V-shaped ring should face the pressure end), and whether there is any damage. If the installation is wrong, install it from the beginning, if it is damaged, replace it from the beginning.

③ Check whether solid impurities are mixed in the sealing cavity and whether the transmission seat is filled with impurities, which will affect the axial floating of the moving ring and the compensation of the spring.

④ Check whether the set screw is loose or not, and whether it affects the normal operation of the mechanical seal.

⑤ Check whether the screws fixing the end cover are loose, which causes the deflection of the sealing end cover.

⑥ Check whether the axial movement and radial runout of the pump exceed the actual technical requirements. ⑦If the shaft sleeve is installed, check whether the seal between the shaft sleeve and the shaft is damaged and whether the orientation is correct.

⑧ Check whether there is sealing liquid circulation in the sealing body, and whether the mechanical seal is in a dry friction state

There are many types of mechanical seals for pumps, and the types are different, but there are five main leakage points:

(l) The seal between the shaft sleeve and the shaft;

(2) The seal between the moving ring and the shaft sleeve;

(3) Seal between dynamic and static rings;

(4) The seal between the static ring and the static ring seat;

(5) The seal between the sealing end cover and the pump body.