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How Mechanical Seals Work

How Mechanical Seals Work


The mechanical seal is a shaft seal device that relies on a pair or several pairs of end faces that are perpendicular to the shaft to slide relative to each other under the action of fluid pressure and the elastic force (or magnetic force) of the compensation mechanism, and is matched with auxiliary seals to achieve leakage prevention.

  The common mechanical seal structure is composed of static ring (static ring) 1, rotating ring (moving ring) 2, elastic element 3, spring seat 4, set screw 5, rotating ring auxiliary sealing ring 6 and stationary ring auxiliary sealing ring 8 and other components , The anti-rotation pin 7 is fixed on the gland 9 to prevent the stationary ring from rotating. Rotating rings and stationary rings are often also called compensation rings or non-compensation rings according to whether they have axial compensation capabilities.

  There are four channels A, B, C, and D in the mechanical seal where the fluid may leak.

  C and D leakage channels are respectively the seals between the stationary ring and the gland, and between the gland and the shell, both of which are static seals. Channel B is the seal between the rotating ring and the shaft. When the end face is worn out by friction, it can only follow the compensating ring for a small amount of movement along the axial direction. In fact, it is still a relatively static seal. Therefore, these leakage channels are relatively easy to plug. The most commonly used static sealing components are rubber O-rings or polytetrafluoroethylene V-rings, and the rotating ring or stationary ring as a compensation ring for auxiliary sealing, sometimes rubber, polytetrafluoroethylene or metal bellows with the function of elastic components Structure.

Channel A is a dynamic seal in which the end faces of the rotating ring and the stationary ring fit together to slide relative to each other. It is the main seal in the mechanical seal device and is also the key to the performance and life of the mechanical seal. Therefore, the processing requirements for the sealing end face are very high. At the same time, in order to maintain the necessary lubricating liquid film between the sealing end faces, the pressure per unit area on the end face must be strictly controlled. If the pressure is too large, it is difficult to form a stable lubricating liquid film, which will accelerate the end face. Wear and tear; pressure is too low, leakage increases. Therefore, in order to obtain good sealing performance and sufficient life, when designing and installing the mechanical seal, it is necessary to ensure that the pressure per unit area of the end face is in the most appropriate range.

Compared with soft packing seal, mechanical seal has the following advantages:

①Reliable sealing

  In the 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 packing seal; ②Long service life

In oil and water medium, it can generally last for 1 to 2 years or longer, and in chemical medium, it can usually last for more than half a year;

③Frictional power consumption is small

The friction power of the mechanical seal is only 10% to 50% of that of the soft packing seal.

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