The main forms of leakage of pump mechanical seals are: leakage due to pressure, leakage due to medium, periodic leakage of mechanical seals, dry friction or grooming of seal face due to insufficient lubricant on seal face, periodic vibration of rotor, and design and selection of mechanical seals caused by other problems. Selection and installation are not reasonable enough.

Analysis of causes and Countermeasures for leakage of mechanical seals of pumps

Mechanical seal itself is a kind of high-precision components, and has high requirements for design, machining, assembly quality. In the use of mechanical seals, we should analyze the various factors of the use of mechanical seals, so that the mechanical seals are suitable for the technical requirements of various pumps and the use of medium requirements and adequate lubrication conditions, so as to ensure long-term reliable operation of the seal.

Definition of mechanical seal of pump: also known as end face seal, it has a pair of end faces perpendicular to the axis of rotation. Under the action of fluid pressure and compensating mechanical external elastic force, the end faces depend on the cooperation of auxiliary seal to keep close to the other end, and relative sliding, so as to prevent fluid leakage.

1. Leakage caused by pressure

(1) The leakage of mechanical seals caused by high pressure and pressure wave will lead to excessive specific pressure of the seal face, difficult formation of liquid film, severe wear of the seal face, increased heat generation and thermal deformation of the seal face when the spring specific pressure and total specific pressure are too large and the pressure in the seal chamber exceeds 3 MPa.

Countermeasure: When assembling machine seal, the spring compression must be carried out according to the stipulation, and the phenomenon of too large or too small is not allowed. The mechanical seal under the condition of high pressure of gear pump should take measures. In order to make the end face force reasonable and reduce deformation as far as possible, we can adopt cemented carbide, ceramics and other high compressive strength materials, and strengthen cooling lubrication measures, choose the transmission mode of * such as keys, pins and so on.

(2) During the start-up and shutdown of the mechanical seal leakage heat conduction oil pump caused by vacuum operation, the negative pressure may occur in the sealing chamber due to the blockage of the pump inlet and the presence of gas in the pumping medium. If the negative pressure occurs in the sealing chamber, the dry friction of the sealing face will occur, and the leakage (water) will occur in the internal mechanical seal. The difference between positive pressure seal and mechanical seal lies in the directional difference of the sealing object, and the mechanical seal also has its adaptability in a certain direction.

Countermeasure: double face mechanical seal is adopted, which helps to improve lubrication conditions and improve sealing performance.

Two. Leakage caused by media.

(1) After the mechanical seals of most submersible sewage pumps are dismantled, the auxiliary seals of the static and dynamic rings are inelastic and some of them have rotted, resulting in a large number of leakage of the mechanical seals and even the phenomenon of grinding the shaft. Due to the high temperature, weak acid and alkali in sewage corrode the static ring and the auxiliary rubber seals of the movable ring, the mechanical leakage is too large. The material of the movable and static ring rubber seals is nitrile-40, which is not resistant to high temperature and acid and alkali. It is easy to corrode when the sewage is acidic and alkaline.

Countermeasures: for corrosive media, rubber parts should be fluorinated rubber with high temperature resistance, weak acid resistance and weak base.

(2) The leakage of mechanical seal caused by solid particle impurities will scratch or accelerate the wear of seal face if solid particle enters the seal face. The accumulation speed of scale and grease on the surface of shaft (sleeve) in high temperature gear pump exceeds the wear speed of friction pair, so that the moving ring can not compensate the wear displacement, and the service life of hard-to-hard friction pair is longer than that of hard-to-hard friction pair. The length of the graphite pair is hard because the solid particles will be embedded in the sealing face of the graphite seal ring.

Countermeasures: in the location where solid particles are easy to enter, tungsten carbide should be used for mechanical seal of tungsten carbide friction pairs.

Three. Periodic leakage of mechanical seals.

The axial movement of the rotor of the explosion-proof self-priming pump is large, the interference between the auxiliary seal and the shaft is large, and the moving ring can not move flexibly on the shaft. After the pump is turned over, the displacement of the moving and static ring is not compensated.

Countermeasure: When assembling mechanical seal, the axial displacement of shaft should be less than 0.1 mm, the interference between auxiliary seal and shaft should be moderate. While ensuring radial seal, the movable ring can move flexibly on the shaft after assembling (the movable ring can spring back freely).

Four. The amount of lubricating oil on the sealing surface is insufficient to cause dry friction or hair sealing ends.

Countermeasures: the height of the lubricating oil surface in the oil chamber should be higher than that of the static and dynamic sealing surface.

Five. Periodic vibration of rotor. The reason is that the stator and upper and lower end covers are not aligned or the impeller and spindle are not balanced, cavitation or bearing damage (wear), this situation will shorten the seal life and produce leakage.

Countermeasures: the above problems can be corrected according to the maintenance standards.

6. There are still some unreasonable places in the design, selection and installation of mechanical seal leakage caused by other problems.

(1) Spring compression must be carried out according to the regulations, not too large or too small phenomenon, error (+2 mm), excessive compression increases end pressure, excessive friction heat, lubricating oil pump caused thermal deformation and accelerated end wear, compression too small static ring end pressure insufficient, can not be sealed.

(2) The end face of the shaft (or sleeve) with the movable ring seal ring and the end face of the seal cover (or shell) with the stationary ring seal ring should be chamfered and trimmed so as to avoid damaging the movable and stationary ring seal ring when assembling.

Seven. Grinding axis phenomenon caused by leakage of small submersible sewage pumps.

(1) The failure of seal of small self-priming centrifugal pump below 715 kW often produces grinding shaft. The position of grinding shaft is mainly as follows: auxiliary seal ring of moving ring, static ring position, and a few springs have grinding shaft phenomenon.