The function of the steam seal

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The function of the steam seal (1): A turbine consists of two main parts: the stator and the rotor. During operation, the rotor rotates at high speed while the stator remains fixed; therefore, a certain gap must be maintained between the rotor and the stator to prevent friction between them. As steam passes through the various stages of the turbine, the pressure and temperature decrease at each stage, resulting in a pressure difference on either side of the partition. When the moving blade has reaction degree, there is also a pressure difference before and after the moving blade. Apart from the majority of the steam flowing through the channels of the guide vanes and moving vanes to do work, a small portion flows through various gaps without doing any work, resulting in losses that reduce the efficiency of the unit. (II) The rotor must also extend out of the cylinder and be supported by bearings, and a gap must be provided in this area as well. At both ends of the high-pressure cylinders and at the front end of the medium-pressure cylinders, the steam pressure inside the cylinders is greater than the external atmospheric pressure; as a result, steam leaks out from these areas, which reduces the efficiency of the unit and causes some loss of condensed water. At the exhaust end of the medium-pressure cylinder and at both ends of the low-pressure cylinder, since the steam pressure inside the cylinders is lower than the external atmospheric pressure, air will leak into the cylinders through the gaps where the main shaft passes through the cylinders. Since air cannot condense in the condenser, this reduces the vacuum level and diminishes the steam’s capacity to do work. (III) In order to reduce air leakage in the gaps mentioned above while ensuring the normal and safe operation of the turbine, various steam seals have been installed. These steam seals can be divided into three main categories: flow-through steam seals, diaphragm steam seals, and shaft-end steam seals. In terms of working principle, all three types of steam seals belong to the labyrinth-type steam seal category. 1--Diaphragm steam seal 2--Encircling belt steam seal