Basic principles, structural design and application fields of mechanical seals

Introduction

Mechanical seal is an efficient sealing device used to prevent fluid leakage. It is widely used in rotating equipment such as pumps, compressors, agitators, and reactors. Mechanical seals achieve sealing by mechanical means and have the advantages of high reliability, low leakage rate, and long service life. This article will introduce the basic principles, structural design, performance characteristics, and main application areas of mechanical seals in detail to help users better understand and use mechanical seals.

1. Basic principles of mechanical seals

1.1 Sealing principle

Mechanical seals achieve fluid sealing through a pair or several pairs of friction pairs of dynamic rings and static rings, using the preload force of elastic elements such as springs or bellows. When the rotating shaft rotates, the dynamic ring rotates with the shaft, while the static ring is fixed to the equipment housing. The close contact between the dynamic ring and the static ring forms a sealing line of defense to prevent fluid leakage from the axial direction.

1.2 Sealing pair

Dynamic ring: usually made of materials such as carbon graphite, ceramics, silicon carbide, etc., and rotates with the shaft.

Stationary ring: usually made of wear-resistant materials such as carbon graphite, ceramics, silicon carbide, etc., and fixed to the equipment housing.

Spring or bellows: Provide preload to keep the dynamic ring and the static ring in close contact.

2. Structural design of mechanical seal

2.1 Basic structure

Dynamic ring assembly: includes dynamic ring, spring (or bellows) and dynamic ring seat.

Static ring assembly: includes static ring, static ring seat and fixing bolts.

Auxiliary seals: such as O-rings, V-rings, etc., used to prevent medium leakage and lubricate the sealing pair.

2.2 Design features

Balanced and unbalanced: According to the pressure distribution of the sealing medium, mechanical seals can be divided into balanced and unbalanced types. Balanced mechanical seals are suitable for high-pressure environments and can effectively reduce the load of the sealing pair.

Container design: Integrate the dynamic ring, static ring, spring (or bellows) and auxiliary seals into one component for easy installation and maintenance.

Multi-stage seal: In high-pressure or high-temperature environments, a multi-stage seal design is used to further improve the sealing effect.

3. Performance characteristics of mechanical seals

3.1 High reliability

Mechanical seals achieve sealing through mechanical means, have high reliability, and can operate stably for a long time under various complex working conditions.

3.2 Low leakage rate

The design of mechanical seals makes them have extremely low leakage rate, which is suitable for occasions with strict leakage requirements, such as chemical, pharmaceutical and other industries.

3.3 Long service life

By selecting wear-resistant materials and optimizing design, the service life of mechanical seals is long, reducing the maintenance and replacement costs of equipment.

3.4 Good corrosion resistance

The dynamic and static rings of mechanical seals are usually made of corrosion-resistant materials, which can resist the erosion of various corrosive media and are suitable for chemical, petroleum and other industries.

3.5 Strong adaptability

Mechanical seals can adapt to different pressures, temperatures and media conditions, and are widely used in various industrial fields.

4. Application fields

4.1 Pump equipment

Centrifugal pumps: Mechanical seals are widely used in the shaft seals of centrifugal pumps, such as chemical pumps, clean water pumps, oil pumps, etc.

Positive displacement pump: such as screw pump, diaphragm pump, etc., mechanical seal is used to prevent leakage between pump body and drive shaft.

4.2 Compressor

Reciprocating compressor: Mechanical seal is used to seal between cylinder and piston to prevent gas leakage.

Centrifugal compressor: Mechanical seal is used for shaft seal to prevent leakage of compressed medium.

4.3 Agitator and reactor

Agitator: Mechanical seal is used to seal the agitator shaft to prevent leakage of agitator medium.

Reactor: Mechanical seal is used for the shaft seal of reactor to prevent leakage of reactants and products.

4.4 Other applications

Fan: Mechanical seal is used for the shaft seal of fan to prevent gas leakage.

Swivel joint: Mechanical seal is used for the seal of rotary joint to prevent medium leakage.

Marine equipment: Mechanical seal is used for the shaft seal of ship pumps and compressors to prevent seawater leakage.

5. Selection recommendations

5.1 Applicable environment

Pressure: Select the appropriate mechanical seal type and material according to the working pressure of the equipment.

Temperature: Consider the influence of medium temperature on mechanical seal, and select high temperature resistant or low temperature resistant materials.

Medium: Choose corrosion-resistant materials such as silicon carbide, ceramics, etc. according to the chemical properties of the medium.

Speed: Choose a mechanical seal suitable for the speed of the equipment, considering the wear and thermal effects of the dynamic and static rings.

5.2 Installation and Maintenance

Installation: The installation of the mechanical seal should be carried out according to the instructions provided by the manufacturer to ensure the centering and parallelism of the dynamic and static rings.

Maintenance: Regularly check the operating status of the mechanical seal, replace auxiliary seals and wear parts to extend the service life.

5.3 Economy

Cost and performance: Although the cost of mechanical seals is relatively high, their excellent sealing performance and long life make them highly economical in long-term use.

Conclusion

As an efficient sealing device, mechanical seals have the advantages of high reliability, low leakage rate and long service life. They are widely used in a variety of industrial equipment such as pumps, compressors, agitators, reactors, etc. When selecting a mechanical seal, its performance and cost should be comprehensively considered according to the specific application requirements and environmental conditions to achieve the best use effect. I hope that the detailed introduction in this article can help users better understand and use mechanical seals.

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