How are mechanical seals formed?

58. How is the mechanical seal formed?

A: the popular mechanical seal of gear oil pump consists of static ring, dynamic ring, compensation buffer mechanism, auxiliary seal ring and transmission mechanism.

The end faces of the static ring and the moving ring are perpendicular to the axis of the pump and fit to each other to form a rotating sealing surface.

Static ring and gland, moving ring and shaft are sealed with auxiliary sealing ring to compensate the buffer mechanism to push the sealing ring along the axial movement, keep the moving ring and the end face of the static ring glued together, and compensate for the wear of the end face of the sealing ring.

59. What are the characteristics of the mechanical seal?

A:

1) good sealing performance, the leakage of mechanical seal is generally 0.01-5ml/h, according to special requirements, after special design, manufacturing of mechanical seal leakage is only 0.01ml/h, or even smaller, and packing seal leakage is 3-80ml/h (according to the relevant provisions of China, when the shaft diameter is not greater than Φ50mm is less than or equal to 3ml/h,

Less than or equal to 5ml/h when the shaft diameter is Φ50mm);

2) Long service life, generally more than 8000h;

3) The friction power is small, only 20%-30% of the packing seal;

4) There is no relative movement between the shaft and the sleeve and the seal, and there will be no friction. The service life of the shaft and the sleeve is long.

5) The sealing surface of the mechanical seal is perpendicular to the pump axis. When the pump shaft vibrates, the seal will produce displacement at any time. Therefore, when the vibration is within a certain range, it can still maintain good sealing performance.

6) mechanical seal depends on the pressure of the sealing fluid and the effect of the spring force, keep the static and dynamic ring sealing surface, and rely on the spring force to compensate for the wear, so once the deployment is appropriate, the pump generally does not need to be adjusted often in the operation, easy to use, maintenance workload is small;

7) Wide range of operating conditions, can be used for high temperature, low temperature, high pressure, high speed and strong corrosion conditions;

8) Troubleshooting and parts replacement is not convenient, can only be repaired after parking;

9) Complex structure, high assembly accuracy, and certain technical requirements for assembly and installation;

10) High manufacturing prices

60. What are the main characteristic parameters of mechanical seals?

Answer: 1) shaft diameter: the shaft diameter range of the pump mechanical seal is generally 6-200mm, special can be up to 400mm, the shaft diameter of the pump is usually determined by the strength requirements of the round or the use of sleeve modulation to meet the mechanical seal standard shaft diameter;

2) Speed: generally the same as the speed of the pump, the speed of the general centrifugal pump is less than or equal to 3000r/min;

High speed centrifugal pump is less than or equal to 8000r/min, special pump is less than or equal to 4000r/min;

3) Average circumferential velocity of sealing face: refers to the circumferential velocity of the average diameter of sealing end face.

The average linear velocity of the sealing surface causes greater heat and wear on the sealing surface (i.e. friction pair).

Generally, the circumferential velocity of the discharge seal is less than or equal to 30m/s;

The circumferential velocity of the spring static mechanical seal is less than or equal to 100m/s;

Special can be less than or equal to 150m/s;

4) end face specific pressure: end face specific pressure PC is the contact pressure on the sealing surface (Mpa).

The specific pressure of the end face seal should be controlled within a reasonable range. Too small will reduce the sealing performance, and too large will aggravate the heat and wear of the sealing surface.

Pump mechanical seal reasonable face specific pressure value: built-in mechanical seal, generally take PC = 0.3-0.6Mpa;

For external mounted type, take PC =0.15-0.4MPa.

When the lubricity is good, the specific pressure of the end face can be increased appropriately. For the liquid with large viscosity, the specific pressure of the end face can be increased appropriately. It is advisable to take Pc= 0.5-0.7Mpa for the liquid with volatile and poor lubricity to take a smaller specific pressure of the end face, and it is advisable to take Pc= 0.3-0.45Mpa.

61. What are the contents of the inspection before the assembly of mechanical seals?

Answer: 1) General inspection: mainly check the model, specification, performance, matching size and whether there is a gap, point pit, deformation and crack and other damage of the parts.

2) the inspection of the dynamic and static rings: the sealing end face should be bright and clean, and defects such as collapse edge, point pit, grooves, scratches, etc.

For the graphite ring, but also immersion without checking whether there is crack.