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How does mechanical seal work

How does mechanical seal work

2023-11-29

Mechanical seal is a shaft seal device that relies on one or several pairs of end faces that slide relatively perpendicular to the shaft to maintain fit under the action of fluid pressure and the elastic force (or magnetic force) of the compensation mechanism and are equipped with auxiliary seals to achieve leakage prevention.


  Commonly used mechanical seal structures are composed of stationary ring (stationary 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 compensating rings or non-compensating rings depending on whether they have axial compensation capabilities.


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


  The C and D leakage channels are the seals between the static ring and the gland, and the gland and the shell respectively. Both are static seals. The B channel is the seal between the rotating ring and the shaft. When the end face is rubbed and worn, it can only follow the compensation ring to make a slight movement in the axial direction. In fact, it is still a relatively static seal. Therefore, these leakage channels are relatively easy to seal. The most commonly used static sealing elements are rubber O-rings or polytetrafluoroethylene V-rings. As the rotating ring or static ring of the compensation ring, rubber, polytetrafluoroethylene or metal bellows that have the function of elastic elements are sometimes used as auxiliary seals. Structure.


Channel A is a dynamic seal in which the end faces of the rotating ring and the stationary ring are in contact with each other and slide relative to each other. It is the main seal in the mechanical seal device and is also the key to determining 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 high, it is difficult to form a stable lubricating liquid film and will accelerate the deterioration of the end face. Wear; if the pressure is too small, the leakage will increase. Therefore, in order to obtain good sealing performance and sufficient service life, when designing and installing a mechanical seal, it is necessary to ensure that the pressure value per unit area of the end face is within the most appropriate range.


Compared with soft packing seals, mechanical seals have the following advantages:


①Reliable sealing


  During 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; ② Long service life


In oil and water media, it usually lasts for 1 to 2 years or more, and in chemical media, it usually lasts for more than half a year;


③Low friction power consumption


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


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