A mechanical seal is a means for preventing leakage of fluid by at least one pair of end faces perpendicular to the axis of rotation which are held and slidably engaged by the fluid pressure and the force of the compensating mechanism (or magnetic force) and the auxiliary seal. Elastic loading mechanism and auxiliary seal is a metallic seal of the mechanical seal we call the metal bellows seal. In the light seal, there is the use of rubber bellows as an auxiliary seal, rubber bellows elastic limited, generally need to supplement the spring to meet the loading elasticity. "Mechanical seal" is often referred to as "mechanical seal."

1. Common leakage phenomenon

Mechanical seal leakage rate of the total maintenance of more than 50% of the pump, the mechanical seal of the operation of a direct impact on the normal operation of the pump, are summarized as follows.

1.1 Periodic leakage

(1) the pump rotor axial large amount of movement, auxiliary seal and shaft of the large amount of interference, dynamic ring can not be flexible in the axis of movement. After the pump is turned, the moving and static rings are worn out, the compensation displacement is not obtained.

Countermeasure: When assembling the mechanical seal, the axle axial movement amount should be less than 0.1mm, the auxiliary seal and the axle's interference quantity should moderate, while guaranteeing the radial seal, the moving ring assembly guarantees after the axis can move flexibly ( The dynamic ring to the spring can be free to spring back).

(2) sealing surface lubricating oil shortage caused by dry friction or nap seal face.

Countermeasures: oil chamber cavity lubricating oil surface height should be added to the dynamic and static ring sealing surface.

(3) the rotor periodic vibration. The reason is that the stator is not aligned with the upper and lower end caps or the impeller and spindle are unbalanced, cavitation or bearing damage (wear), which will shorten the sealing life and cause leakage.

Countermeasures: According to maintenance standards to correct the problem.

1.2 small submersible pump seal leakage caused by grinding shaft phenomenon

(1) 715kW following small pump seal failure often produce grinding shaft, grinding axis position are the following: dynamic ring auxiliary seal ring, static ring position, a small number of springs have grinding axis phenomenon.

(2) the main reasons for grinding axis: ① BIA type double-ended mechanical seal, back pressure state is a bad working condition, the media particles, impurities easily into the sealing surface, the seal failure. ② the main parts of the grinding shaft rubber bellows, and is due to the upper sealing surface is in poor lubrication, static and dynamic friction between the ring torque is greater than the rubber bellows and shaft transmission torque between the relative rotation. ③ moving, static ring auxiliary seal due to the weak acid in the sewage, weak alkaline corrosion, rubber parts have no flexibility. And some have rotten, lost their due function, resulting in the phenomenon of grinding axis.

(3) To solve the above problems, take the following measures: ① to ensure that the lower cover, oil chamber cleanliness, unclean oil to prohibit assembly. ② machine oil seal chamber oil surface line should be higher than the dynamic and static ring sealing surface. ③ According to the different use of different mechanical structure of the mechanical seal. High-lift pump should be redesigned mechanical seal structure, the corrosive medium rubber should be selected with weak acid, weak base of fluorine rubber. Machine sealed static ring should be added anti-pin.

2. Leakage due to pressure

(1) high pressure and pressure waves caused by the mechanical seal leakage As the spring than the pressure and total pressure than the design is too large and the pressure inside the sealed chamber more than 3MPa, will seal the end face than the pressure is too large, difficult to form a liquid film, seal face wear serious , Heat increased, resulting in thermal deformation of the sealing surface.

Countermeasures: In the assembly machine seal, the spring compression must be carried out according to regulations, does not allow too much or too small phenomenon, high pressure mechanical seal should take measures. To make the end force reasonable, minimize deformation, can use cemented carbide, ceramics and other materials with high compressive strength, and strengthen the lubrication of the cooling measures, the choice of * drive mode, such as keys, pins and so on.

(2) the mechanical seal leakage caused by the vacuum state of the pump operation In the start-up process, due to pump inlet blockage, pumping medium containing gas and other reasons, there may be negative pressure sealed chamber, sealed chamber if negative pressure, will (Water) phenomenon, vacuum seal and positive pressure seal is different from the direction of the difference between the sealing object, and the mechanical seal also has a direction of adaptability.

Countermeasures: double mechanical seal, which will help improve the lubrication conditions, improve sealing performance.

3. Leakage due to media

(1) most of the submerged sewage pump mechanical seal dismantling, static ring and moving ring auxiliary seal inelastic, and some have decay, resulting in a large number of mechanical seal leakage and even grinding axis phenomenon. Due to high temperature, weak acid in the sewage, weak base of the static ring and moving ring auxiliary rubber seal corrosion, resulting in mechanical leakage is too large, dynamic and static ring rubber ring material is nitrile-40, Intolerant of acid, alkaline when the sewage is corrosive.

Countermeasures: the corrosive media, rubber parts should be used high temperature, weak acid, weak base of fluorine rubber.

(2) leakage of solid particles caused by the impurity of the mechanical seal If the solid particles into the seal face, will be scratched or speed up the seal face wear, scale and oil accumulation in the shaft (sleeve) surface speed than the friction pair wear rate, resulting in The kinematic rings can not compensate for the wear displacement. The harder pair has a longer service life than the hard graphite pair, because the solid particles are embedded in the sealing surface of the graphite seal ring.

Countermeasures: In the solid particles easy access to the location of the use of tungsten carbide tungsten carbide friction pair of mechanical seals.

4. Mechanical seal leakage due to other problems

(1) the amount of spring compression must be carried out according to regulations, not allowed to have too large or too small phenomenon, the error ± 2mm, the compression is too large to increase the end surface pressure, friction heat too, resulting in sealing surface heat deformation and accelerated end wear , Compression is too small Dynamic ring surface than the pressure is not enough, you can not seal.

(2) Install the ring seal ring shaft (or sleeve) end face and the installation of static ring seal gland (or shell) of the end should be chamfered and repair light, so as not to bump assembly ring collision ring.

5. Mechanical seal should pay attention to the problem

5.1 Installation Precautions

(1) Care must be taken to avoid installation tolerances during installation.

① tighten the gland should be carried out after the alignment of the coupling, bolts should be even on the branch to prevent the gland face deflection, with a feeler to check the points, the error is not greater than 0.05 mm.

② Check the gland and shaft or sleeve with the outer diameter of the gap (ie concentricity), around to be uniform, with a feeler to check the point tolerance is not greater than 0.01 mm.

(2) the amount of spring compression according to regulations, not allowed to have too much or too small phenomenon, the required error of 2.00 mm. Over the General Assembly to increase the end face than the pressure to accelerate the end wear. Too small will result in less than the pressure can not play a sealing effect.

(3) after the installation of dynamic ring, the dynamic ring will be able to automatically spring back to spring back.

5.2 Location requirements during installation

5.2.1 Confirmation of components

The mechanical seal installed on the machine, the installation should be very good before the total assembly with the map in order to confirm whether the parts are ready to complete, then pay attention to seal friction sealing surface, sealing rings and other injuries, defects and other anomalies , But also pay attention to packing, ring (O ring), etc. in contact with the shaft or sleeve surface, flanges and other parts without any scars, if found to have abnormal phenomenon, you must replace or repair before use.

In the actual installation, not more than the required parts to the scene, so that after installation, if any spare parts, it is installed with a leak when the installation; if the lack of spare parts, it means that unnecessary places are assembled On the parts, which also played a role in the installation of self-test.

5.2.2 Mounting position

Installation methods vary with the type of mechanical seal, the type of machine. Will not repeat them here.

5.3 Technical requirements for installation

Mechanical seal is a high-precision mechanical parts, its correct installation and operation of its service life has a great impact. We generally in accordance with the provisions of the Ministry of Petrochemical standards.

Installation of mechanical seals with the mechanical seal with the mechanical seal part of the technical requirements are as follows:

(1) axis bending: the maximum not more than 0.05 mm.

(2) rotor vibration: moving ring seals at the vicinity of the sleeve is not greater than 0.06 mm.

(3) Axial runout of the shaft is not allowed to exceed ± 0.5 mm. If the sleeve is provided, the sleeve is not allowed to loosen.

(4) the alignment error of the coupling: for the gear coupling is not greater than 0.08 ~ 0.10 mm (P2008C), for the flexible coupling is not greater than 0.05 ~ 0.06 mm; (customary end jump <0.05, 0.10).

(5) Gland (static ring seat) and the seal with the center of the axis of the axis of the concentric tolerance of 0.05 mm, with the gasket contact with the center of the plane perpendicular to the value of tolerance 0.03 ~ 0.05 mm, if not To the requirements, sealing cavity to be processed.

(6) The ends of the bushings on which the ring seals are mounted and the ends of the glands (or shells) on which the stationary ring seals are installed should be chamfered and smooth.

5.4 Precautions during disassembly

(1) in the installation, removal of mechanical seals should be careful not to use hand hammer and flat shovel, so as not to damage the sealing element. If the scaling is not removed, it should be cleaned and then removed.

(2) If both ends of the pump with a mechanical seal, in the assembly and disassembly process to take care of each other to prevent the trade-off.

(3) on the operation of the mechanical seal, where the gland is loose to move the seal of the case, the ring parts must be replaced, should not be re-tightened to continue to use. Because the original friction path after the friction will change the contact surface of the seal is very easy to be destroyed.