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Seals form, use range and characteristics

浏览:127 发表时间:2020-03-09 13:47:14


The sealing problem of moving equipment always exists along with the operation of equipment. Today, I have sorted out all kinds of commonly used sealing forms, range of use and characteristics of moving equipment, so that we can have a deeper understanding of the sealing problem.



Pack seal


Parts Notes: 1-bottom lined sleeve 2-packings body 3-liquid seal ring 4-packing 5-gland


Packing seal according to its structural characteristics can be divided into:

Soft packing seal

Hard packing seal

Molding packing seal


1

Soft packing seal


The packing is usually made of a softer thread, which is filled in the sealing chamber by a square strip with a cross-sectional area. The gland produces a compacting force, which compacts the packing, forcing the packing to press on the sealing surface (the outer surface of the shaft and the sealing chamber), producing a radial force of sealing effect, and thus plays a sealing role.

 

Occasions suitable for soft packing: the selected materials of packing filler determines the packing sealing effect, generally packing materials is restricted by PH value and the working medium temperature, pressure, and working surface roughness of the machine, eccentric and linear velocity, etc., 



Graphite disc root can withstand high temperature, high pressure, is one of the most effective products to solve the problem of high temperature, high pressure sealing. Corrosion resistance, excellent sealing performance, and stable and reliable.


Aramid root is a kind of high strength organic fiber woven into the root and then impregnated with polytetrafluoroethylene emulsion and lubricant. Polytetrafluoroethylene (ptfe) packing root is made of pure PTFE dispersion resin as raw material, then twisted, woven into the packing root. It can be widely used in food, pharmaceutical, paper chemical fiber and other high cleanliness requirements, and a strong corrosive medium valves, pumps.

Hard packing seal hard packing seal has two kinds of open ring and split ring.



2

 Hard packing seals
There are two types of hard packing seals: open ring and split ring.


Mechanical seal


Machine seal is always composed of rotating parts (yellow part) and stationary parts (orange part), two relative motion of the moving, static torus as the main sealing surface.

 

Mechanical seal also known as end seal, according to the relevant national standards defined as: by at least a pair of end face perpendicular to the axis of rotation in the fluid pressure and compensation mechanism of the elastic (or magnetic force) action and auxiliary seal under the cooperation to keep the stick while combining with relative sliding, and preventing fluid leakage device.




Dry gas seal

Dry gas seal "dry running gas seal" is a new type of shaft end seal which uses slotted seal technology for gas seal and belongs to non-contact seal. Features: good sealing performance, long life, no need for sealing oil system, low power consumption, simple operation and low maintenance cost. Dry gas seal is the main-body seal of high speed centrifugal compressor in petrochemical industry, which does not need any seal end cooling and lubrication oil. Application: high speed and high speed fluid machinery such as centrifugal compressor, suitable for a small amount of process gas leakage into the atmosphere without harm, such as air compressor, nitrogen compressor, etc.



Labyrinth seal


Labyrinth seal is to set a number of successively arranged circular sealing teeth around the rotating shaft, and a series of closure gaps and expansion cavities are formed between the teeth. The sealed medium can produce throttling effect and achieve the purpose of preventing leakage through the gap of tortuous labyrinth.


 Labyrinth seal is the most basic seal form between stages and shaft ends of centrifugal compressors. According to the different structure characteristics, it can be divided into four types: smooth type, zigzag type, stepped type and honeycomb type.  

1

Smooth labyrinth seal

1.Smooth labyrinth seal

Smooth labyrinth seal haswhole type and inserting type., its structure is simple, easy to manufacture, but poor sealing effect.


2

 Winding labyrinth seal

Winding labyrinth seal has integrate and inserting two types. The feature as:l, sealing gears with different extruding height, high and low gears alternately arranged , the matching surface of the shaft, is a special concave and convex groove. The structure of the high and low gear to match the concave and convex chamfer, make smooth seal clearance into winding type, therefore, increases the resistance to flow, improve the sealing performance. However, it can only be used in the cylinder or partition with horizontal section surface, and the sealing body is also made into horizontal section type.  




3

 Step labyrinth seal 

 3.The step labyrinth seal is similar to the smooth labyrinth seal in structure from the analysis of structure, but the sealing effect is similar to the zigzag labyrinth seal, often used for impeller cover and balance plate.

 


4

Honeycomb labyrinth seal

Honeycomb labyrinth seals  seal tooth welded into a honeycomb shape, to form a complex shape of the expansion chamber, its sealing performance better than the general seal form, suitable for the occasions with big pressure difference, such as centrifugal compressor balance disk seal. The manufacturing technology of honeycomb labyrinth seal is complicated, the sealing strength is high and the sealing effect is good.



Oil seal


Oil seal is a self-tightening type with lip shape, its simple structure, small size, low cost, easy maintenance, resistance torque small, can not only prevent medium leakage, also can prevent external dust and other harmful substances entry, and have certain compensation ability to wear, but not resistant to high pressure, so commonly used in the chemical pump on occasion.



Dynamic seal

Spiral seal

Chemical pump in operation,  the pressure head produced by the deputy impeller  balance high-pressure liquid at the main impeller outlet, so as to achieve sealing. When machine stops, the auxiliary impeller does not work, so must be equipped with a parking seal device to solve the problem that the parking may produce chemical pump leakage. Vice impeller seal structure is simple, reliable, long service life, chemical pump operation can be achieved without leakage.


Spiral seal

Helical seal is also a form of dynamic seal, it is in the rotating shaft or in the shaft on the housing processing spiral groove, between the shaft and the housing filled with sealing medium. The rotation of the shaft causes the spiral groove to act like a pump, thus preventing the leakage of the sealing fluid. The size of its sealing capacity and screw Angle, pitch, tooth width, tooth height, tooth length and the size of the clearance between the shaft and sleeve. Due to the lack of friction between the seals, the service life is long, but due to the limitation of structure space, the screw length is generally shorter, so its sealing capacity is also limited. In the use of pump speed, its sealing effect will be greatly reduced.




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