Various types of seals commonly used in operating equipment, their scope of use, and their characteristics1

Various types of seals commonly used in operating equipment, their scope of use, and their characteristics

1. Type of soft packing for sealing: The packing is usually woven from a relatively soft wire, and is filled in the sealing cavity through a strip with a square cross-sectional area, and the pressing force is generated by the gland. , compress the packing, forcing the packing to be pressed on the sealing surface (the outer surface of the shaft and the sealing cavity), and the radial force of the sealing effect is generated, thus playing a sealing role. Applicable occasions for soft packing: The selected manufacturing material for packing determines the sealing effect of packing. Generally speaking, the manufacturing material of packing is limited by the temperature, pressure and pH of the working medium, and the mechanical equipment used for packing is limited. Surface roughness, eccentricity and line speed, etc., will also have requirements on the material selection of packing. Graphite packing can withstand high temperature and high pressure, and is one of the most effective products to solve the problem of high temperature and high pressure sealing. Corrosion resistance, excellent sealing performance, and stable and reliable action. Aramid packing is a kind of high-strength organic fiber, which is woven into the packing and then impregnated with polytetrafluoroethylene emulsion and lubricant.

2. Hard packing seal Hard packing seal has two types: split ring and split ring.

3. Mechanical seal Mechanical seal structure diagram The mechanical seal is always composed of two parts: the rotating part (yellow part) and the stationary part (orange part). Mechanical seals, also known as end face seals, are defined according to relevant national standards as: at least one pair of end faces perpendicular to the axis of rotation are kept in contact and slide relatively under the action of fluid pressure and the elastic force (or magnetic force) of the compensation mechanism and the cooperation of the auxiliary seal, while The device to prevent fluid leakage is formed. 4. Labyrinth seal The labyrinth seal is a series of annular sealing teeth arranged in sequence around the rotating shaft. A series of interception gaps and expansion cavities are formed between the teeth, and the sealed medium passes through the tortuous labyrinth. The throttling effect is generated when the gap is closed to achieve the purpose of preventing leakage. 1) Smooth labyrinth seal The smooth labyrinth seal has two structures: integral and insert. It has a simple structure and is easy to manufacture, but the sealing effect is poor. 2) Step labyrinth seal The step labyrinth seal is similar to the smooth labyrinth seal from the structural analysis, but the sealing effect is similar to the tortuous labyrinth seal, and is often used in the impeller cover and balance disc. 3) Folding labyrinth seal The zigzag labyrinth seal is also divided into two structures: the whole and the insert. The structural feature of this labyrinth seal is that the protruding height of the sealing teeth is different, and the high and low teeth are arranged alternately, and the matching shaft surface , is a special concave-convex groove. This structure of high and low teeth and concave-convex grooves makes the smooth sealing gap into a zigzag type. Therefore, it increases the flow resistance and improves the sealing efficiency. However, it can only be used in cylinders or partitions with a horizontally split surface, and the sealing body should also be made of a horizontally split type.

4) Honeycomb labyrinth seal The sealing teeth of the honeycomb labyrinth seal are welded into a honeycomb shape to form a complex-shaped expansion chamber. Its sealing performance is better than the general sealing form, and it is suitable for occasions with large pressure difference, such as Balancing disc seals for centrifugal compressors. The honeycomb labyrinth seal has a complex manufacturing process, high strength of the sealing sheet, and good sealing effect. (a) Oil seal oil seal is a self-tightening lip seal with simple structure, small size, low cost, convenient maintenance and small resistance torque, which can not only prevent medium leakage, but also prevent external dust and other harmful Material intrusion, and has a certain ability to compensate for wear, but it is not resistant to high pressure, so it is generally used in chemical pumps in low pressure occasions. (b) Dynamic seal When the chemical pump is in operation, the pressure head generated by the auxiliary impeller balances the high-pressure liquid at the outlet of the main impeller, thereby achieving sealing. When parking, the auxiliary impeller does not work, so it must be equipped with a parking sealing device to solve the possible leakage of the chemical pump during parking. The auxiliary impeller has a simple sealing structure, reliable sealing and long service life, and can achieve no leakage during the operation of the chemical pump. Therefore, it is often used in the chemical pump for conveying impurity-containing media. (c) Spiral seal Spiral seal is also a form of dynamic seal, which is to process a spiral groove on the rotating shaft or on the containing sleeve of the shaft, and the sealing medium is filled between the shaft and the sleeve. The rotation of the shaft causes the helical groove to act like a pump, thereby preventing the leakage of the sealing fluid. The size of its sealing ability is related to the helix angle, pitch, tooth width, tooth height, action length of the tooth and the size of the gap between the shaft and the sleeve. Since there is no friction between the seals, the service life is long, but due to the limitation of the structure space, the length of the spiral is generally short, so the sealing ability is also limited. When the pump is used at a reduced speed, its sealing effect will be greatly reduced.

5. Dry gas seal Features of dry gas seal: Good sealing performance, long service life, no need for sealing oil system, low power consumption, simple operation and low operation and maintenance cost. As a maintenance-free sealing system that does not require any seal end face cooling and lubricating oil, dry gas seals are replacing floating ring seals and labyrinth seals and become the main seal of high-speed centrifugal compressor shaft seals in the petrochemical industry. Applicable occasions for dry gas seals: High-speed and other high-speed fluid machinery such as centrifugal compressors, suitable for working conditions where a small amount of process gas leaks into the atmosphere without harm, such as air compressors, nitrogen compressors, etc.