Due to the presence of abrasive particulate media in a solid-liquid two-phase flow, the use of a general mechanical seal often constitutes the following five hazards: (1) increased wear of the sealing face. Between the sealing surface due to particle leakage into the end, plays the role of abrasive, accelerated sealing surface wear. â‘¡ media-side particle blockage. Due to the accumulation of particles, bridging hinders the movement of the spring, the pin and the auxiliary sealing ring, resulting in a reduction of followability and floating of the compensating ring. â‘¢ air-side particle blockage. Due to the conventional design of the mechanical seal, the gap between the inner diameter of the sealing surface and the shaft (or sleeve) is small, and the leaking solid particles can not be discharged in a timely manner, which can easily accumulate and block the movement of the auxiliary sealing ring, thereby causing the sealing failure. â‘£ abrasion. Refers to the sealing element surface due to the role of abrasive particles generated by local bite, tear. It usually occurs when using softer steel or graphite materials due to the impact of flushing water or sealant. In the case of granular media, occurred even worse; â‘¤ transmission wear. Since these components of the drive pin are in a granular medium, the abrasion of the component itself is exacerbated by the grinding action of the particles during the movement. In the selection, should make the mechanical seal products try to avoid the role of particles, will not produce these five kinds of failure, the mechanical seal to solve the problem of the role of particulate media has two ways: First, the mechanical seal set some additional internal structure or take the auxiliary Measures such as spiral seals, lip seals, sealing fluids, flushing water, tank or tank build up liquid slugs to prevent particle build-up, etc., or external devices such as swirling solids-liquid separators, magnetic filters, Appear, maintain a good working condition mechanical seal. This approach for more important occasions, important equipment can be used. However, due to space constraints or due to excessive consumption of auxiliary equipment, and because of some occasions, the material is not allowed to seal fluid or flush water into the product, you should choose to design a new type of mechanical seal structure, can be directly Used in granular media to meet the sealing requirements of the production process. In order to seal the reliable mechanical seal, long life, simple structure, easy assembly and disassembly, easy adjustment, low cost, the specific methods are as follows: The use of a combination of spring and auxiliary seal. The main advantages are: high elasticity, and the spring is not in contact with the medium, to avoid the problem of particle blockage. In order to ensure that the friction pair has the purpose of abrasion resistance and abrasion resistance in the granular medium, the hardness of the friction material must be higher than the hardness of the abrasive particles. Usually hard and hard pairs can be used, the material can be tungsten carbide or silicon carbide. Compared with tungsten carbide, silicon carbide has higher hardness, better thermal conductivity, good chemical stability, as well as self-lubricating, but the cost is higher. According to the conclusion of AIGoLubiev (former Soviet Union) et al. On the wear mechanism of high hardness friction pair in abrasive granular media, the width of the friction pair should be wider than the average mechanical seal to obtain a higher service life. Dynamic and static ring width equal to help prevent the particles on the sealing end wear and tear, at the same time, there is sufficient area to avoid large mismatch. Therefore, much larger radial and axial runout than conventional mechanical seal faces can be accommodated. Francis pump mechanical seal should be designed for inflow, particulate media outside the seal ring, the centrifugal force and inertia force of the particles, impurities outward movement, throw away from the sealing surface. Different from the general mechanical seal, the gap between the sleeve and the seal ring should be large. When there is material leakage, it can be discharged in time to avoid the accumulation and obstruction of particles. The design of the seal chamber must have adequate space to allow the material in the seal chamber to flow without settling and cooling and lubricating the seal. In order to reduce the media pressure on the seal end face pressure than the impact of the use of balanced mechanical seal structure. End pressure is one of the most important factors affecting the sealing performance and service life. In order to prevent the particle medium from entering the sealing end surface, the amount of leakage increases and the wear of the end surface aggravates, resulting in the failure of the sealing. The pressure on the end surface should be made larger than that of the normal one. But the end pressure is too large, will result in friction surface heating and wear increased, power consumption increases. Design, the end pressure is about 0.3MPa. When using single-end mechanical seal, in order to avoid the hazards of particle impurities, according to different situations need to take flushing, filtration, separation, isolation, insulation and heating and other measures. Rinsing fluid reliability and quality is the key to the success or failure of the seal. If the cleaning solution is injected externally, the working environment of the seal can be improved, but the cleaning solution must be wasted, and the precondition is that the fluid to be transported is allowed to dilute slightly with the processing solution. Petrochemical industry pump shaft seal is roughly divided into contact seal, non-contact seal two categories. Contact seals include packing seals and mechanical seals; non-contact seals with labyrinth seals, spiral seals and vice impeller seals. 80 ~ 90% of petrochemical industry chemical pump using mechanical seal. The use of mechanical seals is an effective way to solve the problems of running, running, dripping, leaking, improving environmental protection, improving working efficiency and reducing production cost. It is one of the indispensable means to realize industrial modernization. Study drip Guangzhou Haotian Chemical Company ZW600-80-type forced circulation pump, flow 2650m3 / h, pump slurry containing 8% to 10% (wt) or even higher salt crystals, the transfer fluid temperature up to 120 â„ƒ. The shaft seal structure comprises a shaft sleeve, a front machine cover, a seal ring, a pump cover, a back machine cover, a water seal cover and two sets of the two sets installed between them in tandem and independent from each other Mechanical seal, mechanical seal 1 Balanced external static compensation ring machine seal, mechanical seal 2 with double-end fork fork machine seal. Kaiping Guangdong Polyester Enterprise Group slurry pump is Roots pump, slurry medium density l350m3 / kg, the outlet pressure 600kPa, motor speed 1500r / min. The seal of the slurry is in the form of a mechanical seal; the EG is used for flushing, and the seal is sealed with a skeleton oil seal to prevent the flushing fluid from leaking. The improvement measures include: changing the seal position of the O ring at both ends of the push ring and adopting the fluorine rubber O ring; using the PTEF material to make a oil seal similar to the frame oil seal, which is installed between the fixing ring fixing seat and the pump body to prevent the pulp Into the moving material, static ring sealing surface. Japan's Mitsubishi Heavy Industries 93A reactor cooling pump (RCP) shaft seal system includes three seals. The first seal (primary seal) is a film-riding end seal that controls leaks and uses a non-contact controlled leak system to provide less deviation over long periods of operation (about 1 year). The role of the No. 1 seal is to reduce the pressure of the coolant from 15 MPa to 0.3 MPa, including the rotary side seal runner and the stationary side seal ring. Joseph L Foszcz from the United States wrote an overview of shaft seals, claiming that the mechanical seal can handle a wide range of fluids at pressures up to 13.8 MPa, speeds up to 50000 rpm and temperatures from -254 to 649 Â° C. Pump applications that do not allow leaks are gaining in popularity. The article gives a typical mechanical seal assembly, including a seal, a seal ring, stationary seal ring, O-ring (2 seal) and so on. Some patent introduction Guangzhou Pump Factory's Chinese utility model patent ZL discloses a combination of sealed leak-free pump includes a rotating spindle, impeller, pump cover, machine cover and other components, the rotating spindle, impeller, pump cover and machine cover Set the parallel set of two sets of mechanical seals, the outer seal is close to the pump cover single-end balanced static compensator (first stage seal), the inner seal is close to the rotating spindle double-sided machine seal The second stage of sealing), the pump installed in the pump by the combination of mechanical seal, the transmission medium and the separation medium separated from the liquid medium to prevent leakage through the rotating shaft to the outer space. U.S. Patent No. 5,501,470, filed by Japan's NIPPON PILLAR PACKING CO., LTD., Discloses a non-contact shaft seal for rotary machines that creates a fluid film seal on the high pressure side of the shaft seal face. A plurality of pressure grooves are arranged in radial or peripheral direction on the rotating sealing surface to generate dynamic pressure in the fluid film. JP filed by Mitsubishi Heavy Industries of Japan discloses a shaft seal suitable for a high-pressure rotary machine in which a high-pressure chamber and a low-pressure chamber are hermetically sealed with a plurality of grooves on the rotating ring so as to rotate the fluid along the rotation shaft Peripheral delivery. Japanese Patent JP filed by Japan NIPPON PILLAR PACKING CO LTD discloses that the shaft sealing device is a two-way machine seal for high-pressure equipment. The first machine seal is inserted into the rotary seal ring by the two-stage sealing member so that the second sleeve can move relatively in the axial direction so that the first stationary side retainer can keep the first stationary seal ring inserted in the first sleeve. This structure can reduce the size and weight.