Must a mechanical seal operate in a liquid environment?
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I’ve heard that mechanical seals must operate in a liquid environment; otherwise, they tend to wear out easily. It is said that when operating in a liquid environment, a liquid film forms on the mechanical seal, and it is this liquid film that meets the sealing requirements. I wonder if it’s like this? Additionally, I’ve seen many vertical reactors in which the material inside is liquid; however, there is a gas chamber at the top, and the mechanical seal does not come into contact with the liquid. Moreover, it can be seen that the mechanical seal is exposed to the air outside the reactor. I really don’t understand how it can still function properly. Please advise, experts.
Mechanical seals are used in pumps; therefore, the gas present inside the container above mentioned has nothing to do with mechanical seals. A mechanical seal is a dynamic seal, as the pump shaft rotates; friction rings are used for sealing in order to prevent leakage from the pump. A mechanical seal indeed requires a liquid to fill the friction surfaces, creating a liquid film that serves for lubrication and sealing. Pumps are equipped with a liquid system for such mechanical seals; the liquid in question is the material that the pump transports. This liquid needs to be under certain pressure in order to fulfill its sealing and lubricating functions. Therefore, liquid is generally taken from the pump’s outlet as the input fluid for the sealing system.
Even mechanical seals used in reaction vessels have an isolation fluid. If exposed directly, it will burn up very quickly. Are you sure what you saw was a mechanical seal rather than a bearing?
The principle of mechanical seals relies on a thin layer of liquid film for sealing; this film possesses dynamic and static pressures, as well as a certain load-bearing capacity. It prevents direct contact between the surfaces of the rotating and stationary rings, reducing the friction coefficient and thereby ensuring effective sealing. In the case of dry friction, it is difficult to form such a liquid film on the surfaces of the rotating and stationary rings, and reliance solely on the lubricity of these surfaces itself does not constitute an ideal friction condition. As for the mechanical seals used in vertical reaction vessels, sealant needs to be added to them; they do not rely on the liquid inside the vessel for lubrication, which is different from pumps. Since the mechanical seals in reaction vessels are of the external type, it is natural that their housing can be seen.
Generally, that’s the case, but dry gas seals are an exception; they also belong to the category of mechanical seals
Generally, the rotation speed of the stirring device in a reaction vessel is low; since the mechanical seal of the reaction vessel does not come into contact with the liquid phase, it is usually not damaged. Although the mechanical seal of a reaction vessel and that of a pump share the same sealing principle, there are significant differences between them in terms of structure and material
Thank you for your detailed explanation; that’s exactly what they said to me when I bought a mechanical seal. Thank you. :)
1. Mechanical seals are divided into contact type, non-contact type, and semi-contact type. The liquid film mentioned by the poster is of the non-contact type. 2. Non-contact: During operation, the stationary and rotating rings of the mechanical seal do not come into direct contact; instead, a liquid film is formed due to the hydrodynamic pressure effect, which prevents the medium from passing through. 3. As for the liquid mentioned by the original poster, if non-contact is intended, then the liquid is necessary, as it is needed to form a liquid film ； If it refers to flushing, then it is not necessary, as flushing is an auxiliary measure that serves purposes such as cleaning and cooling. If the pressure of the medium is not high, the environment is clean, and the working conditions are mild, then flushing may also be omitted. 4. Contactless machine seals: some use a liquid film, while others use a gas film, with air being used to create a layer.
Then just buy a modular mechanical seal – it’s convenient, there’s no need to adjust the compression level manually, and it’s easy to disassemble, replace, and install.