Impurity pump sealing has always been a headache for researchers, with the expansion of the use of impurity pumps, the problem is even more prominent. Due to the impurity particles pump more and more solid particles, the liquid more and more harmful to the nature of these substances than the normal sediment on the shaft and seal corrosion and wear will be more serious shorten the life of the seal, and seal failure, Leakage directly affects the normal operation of the pump and even the personal safety of the operator. To solve the problem of impurity pump seal it is necessary to understand its sealing form. Seal between the rotating pump shaft and the fixed pump shaft seal. The main function of the shaft seal is to prevent high-pressure liquid from leaking out of the pump and to prevent air from entering the pump. Although the shaft seal in the pump does not occupy a large position, but the pump can operate normally is closely related with the shaft seal. If the shaft seal is improperly selected, it not only needs to be repaired frequently during operation but also leaks a lot of liquid being transported and may cause fire, explosion and poisoning accidents due to leakage of flammable, explosive and poisonous liquids. Therefore, the shaft seal structure must be selected reasonably to ensure the safe operation of the pump. Impurities pump shaft seal are the following categories: packing seal, mechanical seal, floating ring seal, and other seals. The following for a variety of seal characteristics to illustrate their application in the impurity pump. Packing seal is the most commonly used sealing mechanism in the general pump, which consists of packing ring, packing sleeve, packing, packing gland, long buckle stud and nut, through the packing and the pump shaft surface contact to prevent the medium through to achieve the purpose of sealing . There are many fine gaps and grooves between the contacting seal pairs. Therefore, applying sufficient pressing force to achieve the necessary seal specific pressure can elastically deform the packing to reduce the gap. As the shaft surface is always a certain degree of roughness, it can not reach the ideal contact with the filler, there must be a slight gap exists, thus forming countless "maze." These tiny zigzag gaps play a "labyrinth effect" on the damping effect of the medium on multiple throttles and the stagnant boundary layer in the gap, resulting in the blocking of the gap and the sealing. It can be seen that the sealing effect is formed in the gap between the media entering the contact surface of the filler and the pump shaft. Leakage of the fluid through the packing seal has three paths: â‘ leakage through the interface of packing and stationary parts; â‘¡ leakage through the packing itself; and â‘¢ leakage through the packing and moving interface. The fluid leaks through the packing and the static interface as well as the fluid leakage through the static seal. Leakage of the fluid through the packing itself is dependent upon the penetration of the fluid being sealed and the internal structure of the packing itself, which can easily occur with braided packing. Leakage through the packing is almost unavoidable when the medium is highly permeable or the medium is gas, but the specific leakage mechanism needs to be further explored. For the vast majority of liquid media, the leak is primarily through the interface between the packing and the moving parts. For the impurity pump, the larger the diameter of the solid particles in the conveyed medium is, the smaller the gap in the pump shaft seal during transportation is. Therefore, it should be noted that when the packing is sealed in a corrosive medium, the corrosive liquid Will penetrate into the packing, and when the packing contains soluble and corrosive impurities, the fine particles will also enter the packing with the liquid, which will cause the wear of the shaft material, and will also be corroded. In particular, when the two materials constituting the pair of friction pairs are both conductors, galvanic corrosion may occur in the electrolyte solution and the corrosion of the shaft may be more accelerated. Therefore, the impurity pump in the transport of toxic, corrosive and valuable liquid, due to the requirements of leakage is small, or even allowed to leak out, can not be filled with packing. Mechanical seal is by two precision machining of the moving ring and the stationary ring end face by the spring in close contact with the shaft to achieve the seal. (Static ring fixed, moving ring with the shaft rotation) So also called face seal. The structure of the mechanical seal is shown in Fig. 1, which is a typical structure of a single-end non-equilibrium large spring mechanical seal. In Figure 1, the moving ring and the stationary ring are the main sealing elements. The moving ring and the stationary ring are generally made of a different hard-wearing material, such as graphite, Teflon to cemented carbide, ceramics, tungsten carbide, nitrogen Silicon, steel and so on. 6 sets of moving ring on the shaft, moving ring outer diameter and drive seat 2 diameter spline connection, drive seat screw 1 is pressed on the shaft, so that shaft rotation, drive seat and moving ring, moving ring and shaft A seal ring between the shaft and the pump body seal ring 8 to prevent leakage of liquid to the outside, moving ring in the spring force and the role of liquid pressure, the pressure in the stationary ring seal to achieve the role of transmission between the seat and the ring Spring Pushing Ring 4 Use adjusting screws (not shown) to adjust the spring pressure to adjust the seal between the moving ring and the stationary ring. In order to prevent static ring rotating gland anti-rotation pin, in order to prevent the ring due to the static rotation of the relative rotation of the friction generated by the high temperature burn-off sealing surface or make the liquid vaporization caused by the dynamic friction between the moving ring and the stationary ring , So generally have to face flush with the liquid cooling. Mechanical seal although the seal is tight and reliable, almost no leakage (up to 3 to 5 drops / min), but improper installation can increase leakage, reduce life expectancy, or even less than the packing seal; mechanical seal compaction degree must be sample requirements, When installing to gently, especially the friction surface to protect, use cotton tissue. Do not use cotton silk (especially cotton with iron at the end of easy to scratch the sealing surface) and hard things rub, hand rub less; friction surface to clean, can not clamp dirt, install a little glycerin to prevent disc brake Or start the pump is not dry on the liquid; check the friction surface, whether damaged, groove, not serious grinding repair. Grind to use a good flat, 8 word grinding; rotation direction, the single spring (large spring) should pay attention to the direction of rotation of the spring, spring tightening direction is right. In particular, multi-stage pump, generally a left-handed, a right-handed, do not make mistakes; before washing the pump rinse, cool down, stop the pump and then rinse, cooling; static ring gap against anti-sales; new mechanical seal Certain run-in, 1 ~ 5 h start leakage larger, run-in should be less than 3 to 5 drops / min. If you also leak larger should check the reasons to be eliminated. Mechanical seal is generally used in flammable, toxic and expensive liquids or high temperature and pressure, low temperature, strong corrosive liquids, which is to make up for the lack of soft packing seal in the impurity pump applications. Impurities in the pump under different conditions with different mechanical seals, such as double-ended seal for corrosion, high temperature, liquefied petroleum gas with solid particles and fibers, poor lubricating properties of media; Exterior seal for viscous media and low pressure occasions . In some cases the mechanical seal should not be used, such as open impeller wheel, the back of the impeller is provided with short radial back blades. And near the front and back of the part, the pump cover and pump body to install a simple replacement liner, the liner according to its degree of wear, can be pushed toward the impeller in the direction of the axis. In this way, the clearance between the impeller and the lining plate can be constantly kept small so that the performance of the pump often reaches high efficiency. Back blades not only serve to relieve the axial thrust of the pump, but their main purpose is to prevent the ingress of powder into the stuffing box by means of centrifugal force. In this case, it is also necessary to inject fresh water into the inside of the stuffing box. Can not get water, had to pump the liquid out of the filter used after filtration. Floating ring seal structure and the mechanical seal is relatively simple. The amount of leakage is between the packing seal and the mechanical seal. Reliable operation, but the axial size slightly larger than the other seal structure. Floating ring seal is the use of floating ring end face and floating sleeve end face to achieve axial seal, as shown in Figure 2: Radial seal is the outer surface of the sleeve and the inner surface of the floating ring to form a narrow gap to produce throttling To seal. Compared with other forms of shaft seals, floating ring seal has the advantage of self-aligning. Because it can be self-aligning, so radial clearance can be made quite small. The gap between the floating ring and the sleeve and the gap length are important factors affecting the amount of leakage. Other forms of sealing is based on the specific circumstances of the work environment, here only speaks several forms of seal. Plus small pump seal is used in large pumps, large pump larger, the structure of the shaft seal will be a corresponding increase in the volume of the parts will affect the pump parts of the processing difficulty, thus affecting the shape of the parts Tolerance and precision, the seal is more difficult than large and medium-sized pump. Sometimes large pumps have large leaks with other types of shaft seals, so a small water pump can be added to the shaft seal of a large pump to drain the leaking fluid. In the impeller plus the back of the seal form, plus the back can not only balance the axial force, but also to prevent the solid particles into the shaft seal play the role of its application to the pump can also make the pump compact, simple appearance , So the solid particles are not large, non-corrosive liquid or less corrosive impurities pump applications. With the continuous development of science and technology, the constant improvement of various technologies and the improvement of impurity pump performance have also broadened the field of its application. As mentioned at the beginning of this article, large particles of solid media, high concentrations of corrosive substances and a mixture of a variety of substances has become the main task of impurity pump delivery, so that a single form of sealing due to the appropriate conditions only slowly out of the mainstream Position, take it over is a combination of a variety of forms of seal in the form of a combination of seals, it can make up for the lack of a single seal to improve the life of the seal part, to adapt to a variety of complex work, to solve a variety of materials on the shaft Corrosion, sealing the situation is also very satisfactory. Therefore, this seal is suitable for complex applications, such as the combination of a labyrinth-helical seal and a mechanical seal used in a long-stroke heavy-duty pump to reduce the pressure of the seal oil and thereby improve the service life of the mechanical seal. Impurity pump shaft seal is the main part of the entire pump seal, which determines whether the normal operation of the pump, but the large variety of seals, the correct choice of the form of shaft seal to rely on experience slowly accumulated. Soft packing seal structure is simple, easy to replace, cheap, but the power consumption, pressure distribution along the uneven axial distribution near the gland at the fastest packing wear, impurities in the pump is generally suitable for sealing the general medium. Mechanical seal, stable performance, almost no leakage (even if the leakage is less than 3 to 5 drops / min), long life, when used properly, the media life of up to 10 000 h. Small resistance, low power consumption, high mechanical efficiency. But the structure is complex, expensive, installation, maintenance requires high technology. Impurities in the pump is generally used for flammable, toxic and expensive liquid or high temperature and pressure, low temperature, strong corrosion of the liquid. Floating ring due to larger size, inlet pressure, high temperature liquid transport mud pump can be used. In other forms of sealing, especially in the combination of sealing a wide range of applications, it has good sealing effect, the use of a wide range of applications in a wide range of complex machinery is increasingly valued today, with the continuous development of science and technology, combined seal Will be developed.
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