First, the dry gas seal Overview Dry gas seal is the late 1960s from the dynamic pressure gas bearings developed on the basis of a new type of non-contact seal. The seal utilizes the principle of fluid dynamics to realize the non-contact operation of the sealing end surface by providing the dynamic pressure groove on the sealing end surface. After years of research, the British company John Crane took the lead in the late seventies to apply dry gas seals to gas delivery equipment on offshore platforms and achieved success. Dry gas seal was originally developed to solve the shaft seal problem of high-speed centrifugal compressors. Due to the non-contact operation of the seal, the friction material of the seal is basically not limited by the PV value and is particularly suitable as a shaft seal for high-speed and high-pressure equipment. With the increasingly mature dry gas sealing technology, its application is also more and more broad, at present, dry gas seal is gradually being applied in centrifugal pumps and blenders. In short, where the use of mechanical seals can be used dry gas seal occasions. Compared with the mechanical seal, dry gas seal has the following advantages: 1, long sealing life, stable and reliable operation; 2, the sealing power consumption is small, only about 5% of the contact mechanical seal; 3, with other non-contact seals Compared to dry gas seal gas leakage is small; 4, the media can achieve zero escape, is an environmentally friendly seal; 5, seal auxiliary system is simple, reliable, use does not require maintenance; Second, the centrifugal pump with dry gas Sealed centrifugal pump to transport the medium for the liquid. According to different working conditions, the following types of seals can be used: 1, double-sided dry gas seal Double dry gas seal can be used in the vast majority of centrifugal pump shaft seal, it has the following characteristics: 1) "Instead of the traditional" liquid obstruction "principle, that is, using pressurized sealing gas instead of pressurized sealing liquid to ensure that the process medium to achieve" zero escape "; 2) complete sealing non-contact operation, the power consumption is only traditional double- 5%, the service life of more than 5 times longer than the traditional seal; 3) A simple structure of the auxiliary system to ensure that the process media is not contaminated and the process medium does not leak to the atmosphere, completely out of the traditional double-sided mechanical seal on the oil system. Sealed gas using industrial nitrogen or industrial instrumentation, the pressure is higher than the medium 0.15-0.2MPa. Pumps with double-sided dry gas seal of the deficiencies are: 1) need a certain pressure of the gas source, gas pressure at least higher than the medium pressure 0.2MPa; 2) a trace of gas into the process. 2, series dry gas seal pump series dry gas seal has the following characteristics: 1) dry gas seal and contact type mechanical seal used in tandem, the mechanical seal is the main seal, dry gas seal is the secondary seal; 2) dry gas seal and The main seal between the access to nitrogen, to ensure that the main seal has a certain back pressure, greatly extending the service life of the main seal; 3) The main seal leakage of process gas discharged into the torch with sealed gas to ensure that the process medium does not leak to the atmosphere, is a Environmental protection; 4) After the failure of the main seal, dry gas seal play a major role within a short time to prevent a large number of process media to the atmosphere leak. 5) The life of this type of seal depends on the service life of the mechanical seal, which is usually about 2-3 years. 6) The seal is mainly used for volatile media occasions, such as liquid hydrocarbon media; less demanding on the seal gas pressure. The inadequacies of this seal are: 1) The seal is not yet a completely dry-gas seal, with the overall performance being between the mechanical seal and the dry seal. 2) The seal is suitable for volatile media occasions, the use of a narrow range.