Some knowledge of o-ring and principle of mechanical seal


Mechanical seals for pumps are widely used in various types of pumps. Mechanical seal is a kind of sealing equipment with high precision, which has a certain demand for equipment and operating conditions.

1.General Guidelines for the Use of Mechanical Sealing Equipment

(1) To clarify the situation of the equipment, it is necessary to know the rotating speed and diameter of the rotating shaft, the manufacturing accuracy of the equipment and the dimension of the sealing chamber, the service life of the equipment itself and the orientation of the equipment in the production process.

(2) Budget medium pressure. The pressure of the sealing chamber of a pump is usually lower than the outlet pressure of the pump rather than the outlet pressure of the pump.

(3) Clarify the sealing medium. It is necessary to know whether the sealing medium is gaseous or liquid, whether the medium contains particles and particles, and the nature and temperature of the medium so as to select the proper type and adopt the necessary cooling, scouring and smoothing methods.

2. Skills Requirement of Mechanical Sealing Equipment

(1) The radial runout of the axle or sleeve in the mechanical seal part of the equipment shall conform to Table 1. The surface roughness of the shaft or sleeve should meet the skill requirement, and the outer diameter scale is h6.

(2) The axial channeling of the transmission shaft does not exceed 0.2 mm.

(3) The end face of the sealing chamber shall be in accordance with Table 2 for the jumping service of the outer surface of the shaft.

Table 1 Radial Runout Service

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

(5) When the temperature of the transport medium is too high, too low or rich in impurity particles, flammable, explosive and toxic, the corresponding methods of blocking, scouring, cooling and filtering should be adopted.

(6) For some mechanical seals driven by tension springs, it is necessary to pay attention to the rotation direction of the tension springs, that is, the rotation direction of the shaft should make the tension springs tighter and tighter. Otherwise, the seal will fail. The selection of the rotation direction of the tension springs is determined by the following methods: from the static ring to the dynamic ring, the axis rotates clockwise with the right-rotation tension springs, and vice versa, the left-rotation tension springs are selected.

3. Equipment Method for Mechanical Seals

Mechanical seal parts are in strict demand both in manufacturing accuracy and equipment accuracy. If the equipment is not suitable, it will affect the life and sealing function of the seal. When the equipment is severe, it will make the seal agile failure.

Preparatory operation before equipment and precautions for equipment

(1) Check whether the type and specification of mechanical seals for equipment are correct, and whether the parts are short.

(2) Check whether the mechanical seal components are damaged, especially whether the sealing faces of the moving ring and the static ring are damaged. If damage is found, it is necessary to repair or replace new parts. The sealing elements should be clean and clean with gasoline or fuel, and adhere to the appearance of the components free of dust and foreign bodies.

(3) Whether there are burrs or grooves on the outer surface of the shaft or sleeve, the inner wall of the sealing chamber and the inner and outer surface of the sealing end cap. If burrs and grooves are found, they should be smoothed and polished, and cleaned with gasoline or fuel oil. They should be kept clean and dust and sundries should not be attached to the surface.

(4) Do not wipe the appearance of moving ring and static ring with unclean cloth or cotton gauze. Use clean and soft gauze, degreased cotton and other things to wipe.

During the process of equipment, we should adhere to cleanliness to ensure that the sealing faces of moving and static rings are not scratched or broken. In order to be more suitable for loading, oil should be altered on the outer surface of the shaft or sleeve, in cooperation with the cover and seal ring, so as to avoid dry conflict at the moment of starting.

Equipment ranking

(1) Assembly of stop parts for mechanical seals:

A. Install the anti-dumping pin into the corresponding hole of the sealing end cover;

B. Put the static ring seal ring on the static ring, and put the static ring into the sealing end cover. Attention should be paid to making the anti-reset pin enter the groove of the static ring. When pressing the cover of the equipment, be careful not to make the static ring touch the shaft. Bolts should be tightened evenly in several turns.

(2) Assembly of rotating parts of mechanical seals: The rotating parts of mechanical seals are assembled on the axles one by one in accordance with the sequence. If there is a sleeve, the rotating parts of the mechanical seal should be assembled on the sleeve sequentially outside, and then the sleeve with the rotating parts of the mechanical seal should be assembled on the shaft.

(3) The end cap is mounted on the sealing body and screwed evenly.

(4) Whether the test run is easy or not, if the test run is not moving or laborious, the equipment scale should be checked to see if it is correct.

4. Disposal of defects in mechanical seal operation

1 Leak at the beginning

(1) Check whether the quality of equipment meets the needs of skills and whether the tightening amount of spring meets the rules.

(2) Check whether the sealing face of the moving ring and the static ring is damaged.

Check whether the seal face is regular.

2 There is a sudden excess of leakage in the operation, so we should check it by parking at the moment.

(1) Look at the wear and tear of the sealing face of the moving ring and the static ring and the change of the external quality. If it has been damaged, it should be repaired or replaced with new parts.

(2) Check whether the equipment orientation of the auxiliary sealing ring of the movable ring and the static ring is correct (e.g. the lip of the V-ring should be oriented towards the pressure end) and whether it is damaged or not. If the installation is wrong, the equipment should be replaced from scratch. If it is damaged, the equipment should be replaced from scratch.

(3) Check whether solid impurities are mixed into the sealing chamber and whether impurities are filled in the transmission seat, which affects the axial floating of the moving ring and the compensation of the tension spring.

(4) Check whether the fastening screw is loose or not, and whether it affects the normal operation of mechanical seals.

Check whether the screw of the fixed end cap is loose, which results in the deflection of the sealing end cap.

See if the axial movement and radial oscillation of the pump exceed the skill requirement.

If the axle sleeve is installed, check whether the seal between the axle sleeve and the axle is damaged, and whether the orientation is correct.

Check whether there is a circulation of sealing fluid in the sealing body. Is the mechanical seal in a dry conflict situation?

The types of mechanical seals used for pumps are various, but there are five main leakage points:

(l) Sealing between sleeve and shaft;

(2) Sealing between moving ring and sleeve;

(3) Sealing between dynamic and static rings;

(4) Sealing between the stationary ring and the stationary ring seat;

(5) Sealing between seal end cover and pump body.