The Mechanical Seal Of Pump

1. What is the mechanical seal of the pump?

The mechanical seal is also called the end-face seal. It is composed of at least one pair of end faces perpendicular to the axis of rotation. Under the action of fluid pressure and compensation mechanism, the two end faces are closely fitted and slide relative to each other to form a device to prevent fluid leakage.


2. What is the basis for selecting the material of the mechanical seal friction pair?

It should be selected according to the nature of the medium, working pressure, temperature, sliding speed and other factors, and sometimes the ability to withstand short-term dry friction when starting or liquid film damage is also considered.


3. What are the components of the mechanical seal of the pump?

The mechanical seal consists of a static ring, a moving ring, a compensation buffer mechanism, an auxiliary sealing ring and a transmission mechanism. The end faces of the static ring and the moving ring are perpendicular to the axis of the pump and fit together to form a rotating sealing surface. The static ring and the gland, the moving ring and the shaft are all sealed with the auxiliary sealing ring, and the compensation buffer mechanism is used to push the sealing ring to move in the axial direction, keep the end faces of the moving ring and the static ring in contact, and check the wear of the end face of the sealing ring compensate.


4. What are the inspections before mechanical seal assembly?

1) General inspection: mainly check the model, specification, performance, matching dimensions of each part and whether there are gaps, pits, deformation and cracks and other damages.

2) Inspection of dynamic and static rings: the sealing end face should be smooth and bright, with defects such as chipped edges, pits, grooves, scratches, etc. For graphite rings, check for cracks by immersion.


5. How to check the parallelism, perpendicularity and surface roughness of the end face?

1) The flatness of the end face is 0.0006-0.0009mm for liquid medium and 0.0001-0.0004mm for gaseous medium;

2) Tolerance of balance degree: the deviation of parallelism between the sealing end and the contact surface of the sealing ring, generally the sealing ring is less than or equal to 0.04mm. The parallelism deviation of both ends of the ring (ceramic ring and hard alloy ring) should be less than or equal to 0.03mm;

3) Perpendicularity tolerance; the verticality deviation of the centerline of the outer diameter of the opposite side where the sealing ring is installed, the full diameter should be less than or equal to 0.03mm;

4) Surface roughness: hard material on the sealing surface (obtained by removing material), dark glossy surface (obtained by grinding), soft material (obtained by removing material), no traces of processing can be seen, micro-discern the processing direction (grinding, precision obtained by turning), the contact with the auxiliary sealing ring (obtained by removing material) is invisible processing traces, the processing direction is micro-discerned (obtained by grinding, fine turning), and the rest are (obtained by removing material) slight knife marks (knife twisted, fine car obtained).


6. What are the inspection contents of the sealing end face or sealing box?

The roughness of the surface in contact with the static ring sealing ring is 1.6. After the static ring is assembled, the circular runout of the end face shall not exceed 0.06mm. The sealing end face or sealing cavity should be free of burrs, and the chamfer radius should be sufficient and smooth. The size of the sealing end face or the inner diameter of the sealing chamber should meet the requirements.


7. What are the precautions for assembling the auxiliary sealing ring?

1) The rubber auxiliary sealing ring cannot be soaked and washed with gasoline or kerosene to avoid swelling, deformation and premature aging;

2) The “o”-shaped sealing ring is installed on the static ring assembly, and it should be straightened without twisting. It is the cross-section when the burr is in a free state;

3) When pushing the assembly, prevent the “o” ring from being damaged. The main damage forms are: falling blocks, cracks, bruises, curling and twisting.


8. What are the reasons for the crack of the mechanical seal “o” ring?

Rough or burred shaft surfaces; old shafts or sleeves damaged by fastening screws and not polished smooth before assembly; edges of keyways and anti-rotation pin grooves not properly trimmed.


9. What are the requirements for debugging the mechanical seal spring compression?

The mechanical seal spring is compressed by the transmission screw, which is called the compression amount of the spring. After all the mechanical seals are installed, they are compressed by an amount relative to the spring, which is called the compression amount of the mechanical seal. The total compression of the mechanical seal spring is the sum of the compression of the drive screw and the spring force of the spring itself. During assembly, the greater the compression of the mechanical seal, the smaller the force of the spring on the moving ring. Therefore, according to the working principle of the mechanical seal, the size of the spring has a great influence on the performance and life of the mechanical seal, so the assembly must adjust the compression amount according to the technical requirements.


10. What precautions should be taken when installing the static ring assembly?

1) Insert the inspected static ring seal ring from the end of the static ring, and put the static ring assembly into the gland or sealing chamber. Under no circumstances should shock be applied to mechanical seal parts or components. The pressed surface should be covered with clean cardboard or cloth to avoid damage to the sealing end surface.

2) After assembling into a rotating type moving ring assembly or a static type static ring assembly, press the compensation ring by hand to check whether it is installed in place and whether it is flexible; whether the elastic opening is positioned reliably.

3) Whether the perpendicularity between the sealing end face and the center line of the shaft or sleeve meets the requirements.

4) For static mechanical seals, the anti-rotation pin leads of the static ring assembly must be accurate. When pushing the static ring assembly, the pin groove of the assembly must be aligned with the pin. After pushing in place, measure the distance from the end face of the assembly to a certain end face of the seal chamber , to determine whether the installation is in place;

5) When tightening the bolts to tighten the end cover, the force should be even and symmetrical, and the screwing should be done several times, and should not be tightened at one time, so as not to deflect or even crush the graphite ring.


11. What are the requirements for inspection after mechanical seal assembly?

After the mechanical seal is assembled, there are two inspections to be done.

1) cranking inspection. Since there is no liquid filling, there is only a very small amount of lubricating oil on the sealing end surface of the dynamic and static rings, so it is not suitable to turn more than one turn, so as not to damage the sealing end surface.

2) Liquid filling check. Check whether there is any leakage, if there is no leakage, do a test run inspection.


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