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The correct choice of mechanical seal is to prevent leakage of the pump (with photos)
For more than 100 years, a variety of packing materials, such as packing, have been used to reduce the amount of liquid leaking out of the pump housing along the major axis. Despite the pumps used in modern processes, the oldest sealed design, the stuffing box, is still widely used because of its low initial cost and familiarity to the plant staff. However, due to the environmental problems, the method of using packing seal has gradually become unacceptable, especially for the more common and corrosive liquids in modern process. Therefore, in practical applications, the use of mechanical seals instead of packing more and more. The basic elements of the seal Mechanical seal is the use of friction between the two planes running principle, to seal the purpose. The rotary sealing surface is installed on the main shaft of the liquid pump, and the fixed sealing surface is installed in the sealing gland. Because one sealing surface is moving while the other sealing surface is stationary, this type of seal is called a dynamic seal. 1. The passage between the sealing surfaces; 2. The passage between the rotating surface and the main shaft; 3. The passage between the fixing surface and the gland; 4. The passage between the gland and the stuffing box. The latter two leak paths generally use static seals because there is no relative movement between the two parts. This part of the seal are usually referred to as the tertiary seal, the sealing material is a gasket or O-ring seal compatible with the process liquid. In older seal designs, the secondary seal, located below the surface of revolution, left some clearance to move back and forth on the spindle, thus easily causing wear and premature failure. However, in newer seal designs, the secondary seal is at rest, thereby avoiding the problem of wear and corrosion on the spindle. During normal operation of the pump, the pressure between the rotating face and the stationary face due to the fluid in the stuffing box keeps it in a sealed condition, and the pressure in the stuffing box is maintained by the pressure generated by the spring during start up and shut down Can even be replaced by the pressure of the spring). Most mechanical seals are designed with a softer material to create a rotating surface that rotates friction on a harder stationary surface. Over the years, the most common combination is the use of carbon material as a rotating surface, so that the ceramic stationary surface running. These types of materials are still in common use today, but stationary faces are made of stainless steel or harder materials such as tungsten carbide or silicon carbide. Regardless of the material used, in any event, a liquid film must be maintained between the contact surfaces to provide lubrication. However, in packing boxes, the combination of spring load and fluid pressure provides a good seal between the sealing surfaces. However, the sealing pressure is too high, it will affect the formation of liquid film between the contact surface, leading to increased heat and premature wear. If the sealing pressure is too low, the gap between the contact surface increases, likely to cause liquid leakage. Seal manufacturers are constantly working to improve the flatness of the contact surfaces, and they use a special polishing plate for grinding. It is then detected using a monochromatic light grid plate. From this point of view, it is important that these sealing surfaces be handled with care and in strict accordance with the installation instructions to ensure that the sealing surfaces are adequately protected and properly seated.