The correct selection of the solid-liquid two-phase flow pump mechanical seal


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Due to the presence of solid-liquid two-phase flow of abrasive granular media, the use of mechanical seals often consisting of the following hazards:

The media side of the particles clogging. Because the accumulation of particles, bridges, hindered the spring pins and auxiliary sealing the movement of the seal ring, resulting in lower compensation ring to follow and floating.

Seals increased wear. Sealing surface between the particles leak into the face, plays an abrasive effect, accelerating the wear of the sealing surface.

(3) atmospheric side of the particle clogging. The conventional design of the mechanical seal, the gap between the inner diameter of the sealing surface and the shaft (or sleeve) is smaller, the leakage of solid particles can not be discharged, easy accumulation, blocking, hindering the movement of the auxiliary seals, resulting in seal failure.

The abrasion. Local etching refers to the surface of the sealing elements arising due to the role of the abrasive particles, torn. It usually occurs in the use of softer steel or graphite materials, caused by the impact of the wash water or sealing liquid. In the case of granular media, the more serious;

drive component wear and tear. Because these components in the drive pin in granular media, the movement intensified the abrasive particles the wear of the components themselves.

Selection, mechanical seal products to avoid the role of the particles will not produce five kinds of failure, the mechanical seal to solve the problem of granular media role there are two ways: First, some additional internal structure of the mechanical seal is set to take supplementary measures (such as spiral seal, lip seal, the sealing liquid, rinse water, water tanks or tank to the establishment of the liquid barrier to prevent particle accumulation), or an external device (such as the cyclone solid-liquid separation, magnetic filters, etc.), try to avoid these five kinds of failure appears, maintain the mechanical seal in good working condition. This way for more important occasions, it is important equipment can be used. However, due to limited space, or consuming too high because of the ancillary facilities, as well as on some occasions, the material does not allow sealing solution or rinse water into the product, should be taken to design a new type of mechanical seal structure can used in granular media, to meet the requirements of the production process sealed.

Mechanical seal to achieve the purpose of sealing, reliable, long life, simple structure, easy assembly and disassembly, easy to adjust, low cost, specific measures are as follows:

Spring and secondary seal used in conjunction. The main advantages are: high elastic, and the spring does not contact with the media to avoid the problem of susceptible particles clogging.

In order to ensure that the friction pair to wear and abrasion resistance, hardness of the friction pair materials must be higher than the hardness of the abrasive particles in granular media. Usually the choice of the hard right, hard group may be made of tungsten carbide or silicon carbide. Compared with tungsten carbide, silicon carbide has a higher hardness and better thermal conductivity, good chemical stability, as well as self-lubrication, but the cost is higher.

According to the conclusions reached by the Institute of AIGoLubiev (former Soviet Union), who wear mechanism of friction pairs in the high hardness of the abrasive particle media, the width of the friction pair should be higher than the general mechanical seal width to obtain a higher service life. Dynamic, static rings of equal width, to prevent the particles on the wear of the seal faces, at the same time, there is enough area to avoid the large mismatch. Therefore, the ability to adapt is much greater than the general mechanical seal faces of the radial and axial runout.

Mixed flow pump with mechanical seal should be designed to flow type, granular media outside of the seal ring, centrifugal force and inertia force particles, impurities outward movement, far better than the sealing surface.

General mechanical seal, the gap between the sleeve and the sealing ring should be larger material leakage can be discharged in time to avoid the accumulation of particles and blocking. Seal chamber must be designed to have appropriate space, cavity sealing material can flow, not the accumulation of precipitation, and easy to cool and lubricate the seal. In order to reduce the media pressure within the pump seal faces than the pressure balanced mechanical seal structure.

Face pressure ratio is one of the most important factors that affect the sealing performance and service life. In order to prevent the granular media into the seal faces, leakage increases, increased face wear, resulting in the failure of the seal, should make the face of pressure ratio than the average to be bigger. But face pressure ratio is too large will result in increased power consumption, heat and wear of the friction surface intensified. Design, end pressure is about 0.3MPa.

When using a single mechanical seal, in order to avoid the hazards of particulate impurities, required according to different situations to take washing, filtration, separation, isolation, insulation and heating measures. The reliability and quality of the washing fluid is sealed key to success. From the outside into the clean flushing fluid, sealed work environment can be improved, but must be the loss of the flushing fluid, and its prerequisite is to allow the transmission of liquid rinse liquid microdilution.

The double mechanical seal, the sealing liquid in the seal cavity, pressure, sealing, lubrication and cooling cycle. The double mechanical seal reliability is high, but high manufacturing costs and installation costs. Most dual-face seal group on the choice of materials has been standardized. In actual use, in the media side of the friction pair on the carbide group or silicon carbide group; pairs at the side of the atmosphere with carbon graphite and nickel chrome steel group.



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