GUIDE
This article provides an overview of the 7 forms of dynamic sealing commonly used in mechanical designs, including gasket sealing, mechanical sealing, dry gas sealing, labyrinth sealing, oil sealing, electrical sealing and spiral sealing.
The issue of sealing in mobile equipment is a constant problem during equipment operation. Today, we specifically organize the various types of sealing forms commonly used in mobile equipment, including their range of use and characteristics, to deepen everyone's understanding of sealing issues.
1. Packaging seal
- 1-bottom bush
- 2- stuffing box
- 3-ring seal
- 4-filling
- 5 glands
- 6 gland screw
According to its structural characteristics, gasket seal can be divided into:
- Soft packaging seal
- Rigid packaging seal
- Molded packaging seal
1). Soft packaging seal
Type: packaging
The problem of sealing mobile equipment is always present during its operation. To help people better understand the problem of sealing, we have organized different types of seals commonly used in mobile equipment, as well as their scope of use and characteristics.
The packaging is normally made of soft yarns interwoven and then filled into a cavity sealed by a strip with a square cross-section. Pressure is created by the gland, which compresses the gasket and forces it to be pressed against the sealing surface (the outer surface of the shaft and the sealing cavity), resulting in a radial force with a sealing effect.
The choice of packaging material affects the effectiveness of the seal. Generally, the materials used for the gasket are limited by the temperature, pressure and pH of the working medium, as well as the surface roughness, eccentricity and linear speed of the mechanical equipment in which the gasket works. These factors will also affect gasket material selection.
Graphite gasket is a highly effective solution for high temperature and high pressure sealing. It is known for its corrosion resistance, excellent sealing performance and stable and reliable operation.
| Applicable medium PH range | 0-14 generally used for dynamic sealing parts |
|---|---|
| Graphite Packaging Temperature | -100℃ -850℃ |
| Graphite Packing Pressure | 0-30.0MPa |
Aramid packaging is a type of high-strength organic fiber. Next, the braided gasket is impregnated with PTFE latex and lubricant.
| Applicable medium PH range | 2-13 Suitable for dynamic sealing parts containing solid particles |
|---|---|
| Graphite Packaging Temperature | 260℃ |
| Graphite Packing Pressure | 10.0 MPa |
PTFE packaging is made of pure PTFE dispersion resin as raw material. The raw material film is produced first, then twisted, braided and woven into packaging material. It is widely used in valves and pumps in industries with high cleanliness requirements, such as food, pharmaceuticals, papermaking and chemical fiber, and can deal with strong corrosive media effectively.
two). Rigid packaging seal
There are two types of rigid gasket seals: opening loop and split loop.
The gap ring is a self-tensioning metal sealing ring used in piston machines as piston rings and in rotary machines as expansion rings. The split ring is a cylindrical surface contact dynamic seal that can be used as a rotary dynamic seal for steam turbines and aircraft engines, as well as an alternative seal for steam engines, internal combustion engines and piston compressors (seal between the piston rod and cylinder).
Stuffing box main structure
- Arranged between the compressor cylinder and the intermediate body
- Vacuum sealing pressure up to 3000bar
- Lubrication, cooling, shielding gas and leak recovery can be configured as needed
Classification of packing rings
- Sealing ring
- Choke ring – used in high temperature and high pressure occasions to prevent deformation and loss of non-metallic sealing rings
- Decompression ring – achieve the purpose of decompression by blocking the flow
2. Mechanical Seal
The mechanical seal normally comprises two components: the rotating component (yellow part) and the stationary component (orange part).
The components move relative to each other, with the stationary surface of the ring serving as the seal's primary sealing surface.
Mechanical seals are also called face seals.
According to relevant national standards, they are defined as devices consisting of at least one pair of end faces perpendicular to the axis of rotation. These end faces are kept in contact and move relative to each other with the cooperation of fluid pressure, the elastic or magnetic force of the compensation mechanism, and an auxiliary seal, thus preventing fluid leakage.
The basic components that make up a mechanical seal are:
- Static ring
- Dynamic Ring
- Gland
- pressure ring
- Spring
- Positioning ring
- axle sleeve
- Dynamic Ring Seal
- Static ring seal ring and other components
3. Dry gas seal
Dry gas seal is a new type of shaft end seal that uses slotted seal technology for gas sealing and falls into the category of non-contact seals.
Key features include:
- Excellent sealing performance
- Long service life
- No need for a sealing oil system
- Low energy consumption
- Easy operation
- Low maintenance costs
As a maintenance-free sealing system that does not require lubricating or cooling oil for the sealing end surfaces, the Dry Gas Seal is rapidly replacing the floating seal ring and labyrinth seal as the primary shaft seal for compressors. high speed centrifuges in the petrochemical industry.
Forms:
The Dry Gas Seal is ideal for use on centrifugal compressors and other high speed fluid machines where a small amount of process gas leakage into the atmosphere is acceptable, such as air compressors and nitrogen compressors.
4. Labyrinth Seal
The labyrinth seal is a series of annular seal teeth arranged in sequence along the rotating shaft. These teeth create a series of interception gaps and expansion cavities between them.
The Labyrinth Seal features a series of annular sealing teeth arranged in a circular pattern along the rotating shaft. These teeth create a series of gaps and cavities that act as seals.
Labyrinth seals are the simplest form of sealing between the stages and shaft ends of centrifugal compressors.
Based on their structural characteristics, Labyrinth seals can be classified into four types: smooth, zigzag, stepped and honeycomb.
1). Soft labyrinth seal
The Smooth Labyrinth Seal comes in two structures: integral and panel. It has a simple design and is easy to manufacture, but its sealing performance is limited.
two). Zigzag labyrinth seal
The Zigzag Labyrinth Seal also has two structures: integral and panel.
This type of labyrinth seal is characterized by its alternating arrangement of high and low seal teeth, with different protrusion heights. The corresponding surface of the shaft is a special concave-convex groove.
The arrangement of high and low teeth with the concave and convex grooves transforms the smooth sealing gap into a zigzag shape, resulting in greater flow resistance and better sealing efficiency.
However, it can only be used on cylinders or partitions with a horizontal dividing surface and must be constructed as a horizontal dividing type.
3). Stepped labyrinth seal
Step Labyrinth Seal has a similar structure to Smooth Labyrinth Seal, but its sealing performance is similar to Zigzag Labyrinth Seal. It is commonly used on impeller cover and balance plate.
4). Honeycomb labyrinth seal
The teeth of the Honeycomb Labyrinth Seal are welded together to form a complex honeycomb-shaped expansion chamber.
This type of labyrinth seal offers superior sealing performance compared to other forms of sealing and is ideal for applications with significant pressure differences, such as sealing the balance plate of a centrifugal compressor.
Honeycomb Labyrinth Seal has a complex manufacturing process, but has a high strength seal sheet and excellent sealing capabilities.
5. Oil Seal
Oil Seal is a self-tightening lip seal that features simple design, small size, low cost, easy maintenance and low resistance torque.
This type of seal is used to prevent the leakage of a medium and the intrusion of external dust or other harmful substances. It also has limited compensation for wear, but is not suitable for high pressure applications.
As a result, it is commonly used in low pressure applications in chemical pumps.
6. Energy Seal
During operation, the pressure generated by the auxiliary impeller of the chemical pump balances the high-pressure liquid at the outlet of the main impeller, achieving a seal. However, when the pump stops, the auxiliary impeller stops working, so it must be equipped with a parking seal to resolve possible leaks that may occur during downtime.
The auxiliary impeller has a simple sealing structure, providing reliable sealing and long service life. With its ability to prevent fluid leakage, it is often used in chemical pumps that transport media containing impurities.
7. Spiral Seal
Spiral seals are a type of dynamic seals.
A spiral groove is machined into a rotating shaft or a shaft containing sleeve, and a sealing medium is filled between the shaft and the sleeve.
The rotation of the shaft causes the spiral groove to have a pump-like effect, thus preventing leakage of the sealing fluid.
Its sealing performance depends on spiral angle, pitch, tooth width, tooth height, tooth length and gap between shaft and sleeve.
As there is no friction between the seals, it has a long service life. However, due to structural space limitations, the length of the spiral is generally short, thus limiting its sealing capacity.
When the pump is operated at reduced speeds, its sealing effectiveness is greatly reduced.
