Liquid film mechanical seal-

Liquid film mechanical seal

　2017-11-29　　

Liquid film mechanical seal:

Liquid film mechanical seals generally refer to full liquid film lubrication non-contact mechanical seals, which can reduce or eliminate the leakage of the sealed medium, and at the same time improve the lubrication condition and operational stability of the seal end face. In the liquid film mechanical seal, the upstream pumping mechanical seal (also called the countercurrent pump mechanical seal) is a typical representative. Compared with ordinary contact mechanical seals, liquid film seals can achieve zero leakage or zero escape of the sealed medium, completely eliminate environmental pollution, and have a service life that is several times longer, operation and maintenance costs are greatly reduced, and economic benefits are obvious And other technical advantages have been gradually used in related fields, such as preventing the leakage of harmful liquids to the external environment, preventing solid particles in the sealed liquid medium from entering the sealing end face, using liquid to seal the gas phase process fluid, or ordinary contact type mechanical seals. Competent high-speed and high-pressure sealing conditions, etc. The linear velocity of this type of sealing application has reached 40m/s, the pumping rate range is 0.1-16mL/min, and the process fluid medium pressure for pumping a small amount of low-pressure isolation fluid has reached 10.34MPa. EA100 mechanical seal

The upstream pumping mechanical seal with liquid film lubrication, to put it simply, is that the end face of the ordinary mechanical seal is replaced by a low-flow, high-pressure 'end pumpThe end surface is transported to the sealed cavity. The upstream pumping mechanical seal is divided into two types: zero leakage upstream pumping mechanical seal and zero leakage upstream pumping mechanical seal. The zero-leak upstream pumping mechanical seal does not need an additional buffer auxiliary system, and is mainly used to seal non-flashing hydrocarbons (such as various normal temperature oils, aqueous solutions) and other non-vaporizable media; and zero-leak upstream pumping machinery The seal needs a buffer fluid auxiliary system, which is suitable for sealing easily vaporized media such as flashing hydrocarbons (such as ethylene, catalytic liquid hydrocarbons, liquefied vapor, liquid ammonia, butane), which can completely eliminate the discharge of media to the outside world in any type At the same time, it allows a small amount of buffer to be pumped into the sealed medium without affecting the process production and product quality.

The working principle of the upstream pumping seal is similar to the gas film seal. The liquid is pumped between the sealed end faces by the viscous shear action of the fluid dynamic pressure groove opened on the end face under the rotating condition, so that the pressure of the liquid film is increased and the two sealed end faces are separated. The difference with the gas film seal is that the fluid dynamic pressure groove on the end face of the upstream pumping seal reverses the sealed medium that leaks from the high pressure side to the low pressure side to the high pressure side, or pumps the buffer fluid on the low pressure side in a small amount. To the high-pressure sealed medium side, the leakage of the sealed medium from the high-pressure side to the low-pressure side can be eliminated. It can be seen that the upstream pumping seal is a pump-out non-contact seal structure.

Figure 3-10 The end face structure of the upstream pumping mechanical seal commonly used

Figure 3-10 shows the structure of the spiral groove end surface. If the outer diameter side of the moving ring is a high-pressure sealed liquid (specified as the upstream side or the high-pressure side), the inner diameter side is a low-pressure fluid (gas or liquid, specified as Downstream side or low pressure side>, when the moving ring rotates in the direction shown in the figure, under the action of the spiral groove viscous fluid dynamic pressure effect, a very thin fluid film is formed between the end faces of the moving and static rings (he shown in the figure) ), keep the end faces of the dynamic and static rings separated, that is, in a non-contact state. Under the action of the pressure difference between the outer diameter and the inner diameter, the high-pressure sealed liquid generates a pressure difference flow Qp from outside to inside, and the spiral groove fluid dynamic pressure effect The direction of the viscous shear flow Qs is from the inner diameter to the outer diameter, which is opposite to the direction of the differential pressure flow Qp, so as to realize the function of upstream pumping. 　　611.html,

Types of non-contact gas film mechanical seals 　　 mechanical seal film pressure distribution