EnglishFor special media like easily decomposable ones,crystallizable ones and or so, selection of mechanical seals are quite different.The following will do an analysis:
1. Easily decomposable medium
For easily decomposable media, such as some hydrocarbons, when temperature is ≥175℃, it will be carbonized in contact with air;when temperature is ≥260℃,in contact with air it will polymerize and crack to form a viscous wax-like and solid plastics.
The method to prevent this is:
(1) adopt metal bellow mechanical seals,
(2) Use hot steam for quanching, and the steam must be assured to be continuously rushed to the sealing end surface.
(3) For medium with higher temperature, steam cooling is still required when the whole device is stopped.
2. Solid medium at room temperature
For media that are solid at room temperature, such as heavy hydrocarbons, caprolactam, sulfur, etc., the following measures can be considered:
(1)Adopt heating jacket.
(2) Use a static type mechanical seal while at the same time using hot steam quenching, and ensure that the steam is continuously rushed to the sealing end surface.
(3) The sealing seat should also be heated.
(4) Ensure that the medium works in a liquid state when the whole device is in operation.
3. Crystallizable media
For medium that is easy to crystallize when temperature drops, it should be ensured that temperature of the inner sealing face is always above the saturation temperature, and steam quenching should be adopted.
For medium that is easy to crystallize when temperature drops and cannot be melted though heated, such as carbamate and caprolactam, the solution is to use a static type metal bellow mechanical seal, heat the sealing gland, take steam quenching, and set an anti-coking baffle to prevent coking.
4. Incompatible media
Incompatible media refers to media containing two or more mutually insoluble components,such as oil and water.
The following measures can be considered:
(1)Use heavy-duty driving element.
(2)Matching material should be bronze to tungsten carbide or SiC to CW. Because liquid films formed by this kind of medium between end faces of the mechanical seal is extremely unstable,thus forces subjected by the stationary seat and rotary face are also extremely unstable.
5. Polymerizable liquid
Regardless of their other attributes，the following measures must be taken when liquids easy to polymerize are concerned:
(1) Take measures to prevent the occurrence of polymerization.
(2) Generally, pressurized double bellows mechanical seal should be adopted.
(3) Adopt narrow sealing end surface (knife-shaped ones have good performances, of course,they are also fragile).
(4) The mating material should be hard, such as SiC to SiC, or TC rotary face to SiC stationary seat.
1. Easily decomposable medium
For easily decomposable media, such as some hydrocarbons, when temperature is ≥175℃, it will be carbonized in contact with air;when temperature is ≥260℃,in contact with air it will polymerize and crack to form a viscous wax-like and solid plastics.
The method to prevent this is:
(1) adopt metal bellow mechanical seals,
(2) Use hot steam for quanching, and the steam must be assured to be continuously rushed to the sealing end surface.
(3) For medium with higher temperature, steam cooling is still required when the whole device is stopped.
2. Solid medium at room temperature
For media that are solid at room temperature, such as heavy hydrocarbons, caprolactam, sulfur, etc., the following measures can be considered:
(1)Adopt heating jacket.
(2) Use a static type mechanical seal while at the same time using hot steam quenching, and ensure that the steam is continuously rushed to the sealing end surface.
(3) The sealing seat should also be heated.
(4) Ensure that the medium works in a liquid state when the whole device is in operation.
3. Crystallizable media
For medium that is easy to crystallize when temperature drops, it should be ensured that temperature of the inner sealing face is always above the saturation temperature, and steam quenching should be adopted.
For medium that is easy to crystallize when temperature drops and cannot be melted though heated, such as carbamate and caprolactam, the solution is to use a static type metal bellow mechanical seal, heat the sealing gland, take steam quenching, and set an anti-coking baffle to prevent coking.
4. Incompatible media
Incompatible media refers to media containing two or more mutually insoluble components,such as oil and water.
The following measures can be considered:
(1)Use heavy-duty driving element.
(2)Matching material should be bronze to tungsten carbide or SiC to CW. Because liquid films formed by this kind of medium between end faces of the mechanical seal is extremely unstable,thus forces subjected by the stationary seat and rotary face are also extremely unstable.
5. Polymerizable liquid
Regardless of their other attributes，the following measures must be taken when liquids easy to polymerize are concerned:
(1) Take measures to prevent the occurrence of polymerization.
(2) Generally, pressurized double bellows mechanical seal should be adopted.
(3) Adopt narrow sealing end surface (knife-shaped ones have good performances, of course,they are also fragile).
(4) The mating material should be hard, such as SiC to SiC, or TC rotary face to SiC stationary seat.
