When steam of a certain pressure flows through the steam seal, it must pass through the narrow gaps formed by the teeth of the steam seal and the shoulder of the shaft. When passing through the gap, the flow area decreases, the steam flow rate increases, and the pressure reduce. Then the high-speed steam flow enters the small chamber, the flow area suddenly becomes larger, the flow speed decreases, the steam flow turns, collisions and vortices occur, the speed drops to approximately zero, and the kinetic energy of the steam is converted into thermal energy. As the steam passes through other steam seal gaps, the pressure drops gradually until it is almost the same as atmospheric pressure. Therefore, under a certain pressure difference, the more steam seal teeth there are, the smaller the pressure difference before and after each tooth, and the smaller the amount of steam leakage.