WHAT DO YOU KNOW ABOUT THE ADVANTAGES AND DISADVANTAGES OF MECHANICAL SEALS AND THEIR DEVELOPMENT HISTORY?

The mechanical seal is a shaft seal device used for rotating fluid machinery. It is used for equipment such as centrifugal pumps, centrifuges, reactors, compressors, etc., there is a circumferential gap between the shaft and the equipment cavity, and the equipment medium leaks from it. Therefore, a leakage blocking device must be equipped. Since the mechanical seal has advantages of less leakage and long life, it has become the main shaft sealing method, also known as end seal.

Definition in relevant national standards: it is a device for preventing fluid leakage, which is consists of at least one pair of end faces perpendicular to the axis of rotation, under the joint action of fluid pressure and elastic force (or magnetic force) of the compensation mechanism, and the cooperation of the auxiliary seal ring, the pair of end faces remain attached and relatively slide.

1. Development History of Mechanical Seals

The machine that promoted the development of the industrial revolution was the steam engine, and its basic movement is reciprocating. It wasn't until the invention of the electric motor that the rotary motion equipment really appeared.

The sealing of reciprocating machines and equipment was achieved by various compression packing or improvement of compression tools, such as herringbone rings. The materials are all natural, such as leather, cotton and hemp fibers. Even if artificial materials are used instead of natural materials, the sealing method of reciprocating equipment is basically the same as before.

The earliest fluid conveying pipelines were aided by gravity, and many early post-industrial revolution factories were built on some natural slopes. If the drainage ditch is at the bottom of the slope, the conveying will become easier.

However, in addition to the scarcity of natural resource advantages, there are many other reasons that make the pump become the main method of liquid delivery gradually. It was initially used in reciprocating machines and then used in rotary motion equipment. At that time, pump seals appeared.

The original form of rotary pump packing is compression packing, which is still in use today. However, until the 1930s, pump manufacturers and compression packing manufacturers had a new idea of using a moving ring to rotate against a static ring to make a liquid seal. So the mechanical seal was born.

Although from the current perspective, the design of the early mechanical seal is very rough compared to the current new-generation mature product. But the basic principles and components are similar. The material is bronze or brass.

In the 1940s and 1950s, with the rapid development of the petroleum, chemical and pharmaceutical industries, the demand for machinery and equipment was increasing, and the demand for sealing products also increased greatly, such as spring seals, elastomer bellow seals, etc. Of course, the development of mechanical seals is also keeping pace with the times, but the development is more limited to structural materials rather than design. Therefore, our mechanical seal today has truly become an extremely important and exquisite mechanical equipment, especially with the consideration of environmental issues, the improvement of function becomes particularly important.

2. Advantages and Disadvantages of Mechanical Seals

Advantages:

1) Reliable sealing in long-term operation. The sealing state is very stable, and the leakage is very small. According to rough statistics, the leakage is generally only 1/100 of the soft gland packings.

2) Long service life. It is generally up to 1 ~ 2 years or more in oil and water media, and usually more than half a year in chemical media.

3) Low friction power consumption. The friction power of the mechanical seal is only 10% to 50% of the soft gland packings.

4) The shaft or bushing is basically free from friction.

5) Long-term maintenance cycle. It can automatically compensate after the end face is worn. Under normal circumstances, no frequent maintenance is required.

6) Good vibration resistance. It is not sensitive to the vibration, deflection of the rotating shaft and the deflection of the shaft to the sealed cavity.

7) Wide application range. Mechanical seals can be used for sealing at low temperature, high temperature, vacuum, high pressure, different speeds, and various corrosive media and media containing abrasive particles.

Disadvantages:

1) The structure is relatively complex, and the requirements for manufacturing and processing are high.

2) Installation and replacement are more troublesome and require workers to have a certain level of installation skills.

3) When an accident occurs, it is more difficult to handle.

4) High one-time investment.