Español
Pусский
Liquid hydrocarbon in cryopump is a low temperature liquefied gas, which has characteristics of low boiling point, low viscosity, and high vapor pressure. In mechanical seal used under this working condition, the seal material will appear cold and brittle, water vapor in the atmosphere will freeze on atmospheric side of the sealing device, and liquid film on end surface of the friction pair is easy to vaporize.Especially when the medium leaks slightly, the leaked liquid hydrocarbons will immediately vaporize on the atmospheric side, taking away a lot of heat, and the temperature of the mechanical seal environment will drop sharply.
General sealing materials, such as rubber or polytetrafluoroethylene, will generally become brittle, resulting in sealing failure and increased leakage.
Some companies use double mechanical seals to set up an isolation chamber between the medium and the atmosphere, and seal oil between them to alleviate the effects of low temperatures. However, the mechanical seal of this structure is complicated to install, and it also needs to be equipped with a sealing liquid system, the use temperature is also limited, and the cost is relatively high.
According to actual experience, adopting metal bellow mechanical seals is better. It is mainly manifested in use of metal bellows and flexible graphite instead of auxiliary sealing rings, which solves the problems of cold brittleness and loss of elasticity and buffering of the sealing ring materials, such as the use of DBM, YH604/606/609 type ect.
The following points should be paid attention to when selecting metal bellow mechanical seals for liquid hydrocarbon pumps: 1. Since gasification at the end face of the friction pair has a great influence on the performance of the mechanical seal under low temperature conditions, in addition to selecting more suitable materials, a reasonable end face pressure should be selected.
This mainly refers to compression of the bellows, which is generally 15%-30% larger than the compression given in normal use. Cooling water at about 25°C should be passed into the mechanical seal element close to the atmosphere to improve the lubrication environment of the friction pair;
The metal bellows material should be made of Hastelloy-C (heat-resistant nickel-based alloy), AM350, Carpenter20, etc for they are of low temperature resistance and good toughness; The selection of friction pair materials in two special situations: ① For continuous-running equipment, if the medium contains much solid particles, it is better to use the "hard-to-hard" structure. In practical applications, if YG6 YG6 is adopted, general continuous operating life is more than 800Oh; ②For intermittent operating equipment, use tungsten carbide or silicon carbide vs special graphite as friction pairs are ok.
When installing the cryopump, the mechanical seal, impeller, bearing and other pump parts must be cleaned with solvent and dried before installation. Water and grease are strictly prohibited.
General sealing materials, such as rubber or polytetrafluoroethylene, will generally become brittle, resulting in sealing failure and increased leakage.
Some companies use double mechanical seals to set up an isolation chamber between the medium and the atmosphere, and seal oil between them to alleviate the effects of low temperatures. However, the mechanical seal of this structure is complicated to install, and it also needs to be equipped with a sealing liquid system, the use temperature is also limited, and the cost is relatively high.
According to actual experience, adopting metal bellow mechanical seals is better. It is mainly manifested in use of metal bellows and flexible graphite instead of auxiliary sealing rings, which solves the problems of cold brittleness and loss of elasticity and buffering of the sealing ring materials, such as the use of DBM, YH604/606/609 type ect.
The following points should be paid attention to when selecting metal bellow mechanical seals for liquid hydrocarbon pumps: 1. Since gasification at the end face of the friction pair has a great influence on the performance of the mechanical seal under low temperature conditions, in addition to selecting more suitable materials, a reasonable end face pressure should be selected.
This mainly refers to compression of the bellows, which is generally 15%-30% larger than the compression given in normal use. Cooling water at about 25°C should be passed into the mechanical seal element close to the atmosphere to improve the lubrication environment of the friction pair;
The metal bellows material should be made of Hastelloy-C (heat-resistant nickel-based alloy), AM350, Carpenter20, etc for they are of low temperature resistance and good toughness; The selection of friction pair materials in two special situations: ① For continuous-running equipment, if the medium contains much solid particles, it is better to use the "hard-to-hard" structure. In practical applications, if YG6 YG6 is adopted, general continuous operating life is more than 800Oh; ②For intermittent operating equipment, use tungsten carbide or silicon carbide vs special graphite as friction pairs are ok.
When installing the cryopump, the mechanical seal, impeller, bearing and other pump parts must be cleaned with solvent and dried before installation. Water and grease are strictly prohibited.
