As a rotating machine, the mechanical seal device of water pump in thermal power plant must have a gap between the rotating shaft and the pump casing. In order to prevent liquid from flowing out of the pump or air from leaking into the pump, the shaft seal device is generally set between the shaft and the pump casing in the pump (the inlet is vacuum). With the development of thermal power plant units towards ultra-high parameters and large capacity, power plant pumps are also progressing towards large-scale, high parameters and energy conservation. In pump machinery, shaft end seal is one of the key technologies.

　　The leakage of shaft seal not only wastes energy and raw materials, but also pollutes the environment. Therefore, people pay more and more attention to the sealing technology. Especially the mechanical seal, which is an advanced shaft seal form for energy conservation, leakage control, pollution prevention and safety protection. Expanding and popularizing the use of mechanical seals is an effective way to solve the problems of running, emitting, dripping and leaking, improve environmental protection, improve work efficiency and reduce production costs, and is one of the indispensable means to achieve industrial modernization.

　　The improvement of medium parameters also puts forward higher requirements for shaft end seals of pumps of different purposes and types in thermal power plants. The traditional soft packing seals (mainly asbestos packing and carbon packing seals) of pump equipment are more replaced by mechanical seals with low energy consumption, reliable performance and superior sealing effect. At present, the shaft seal devices used generally have the following forms: packing seal, mechanical seal, labyrinth seal, floating ring seal, and mechanical seal is used for most single-stage cantilever centrifugal pumps in many thermal power plants.