During the maintenance of water turbine generator unit, one maintenance item of water turbine is maintenance seal. The seal for maintenance of hydraulic turbine refers to a bearing seal required during shutdown or maintenance of hydraulic turbine working seal and hydraulic guide bearing, which prevents backflow into the turbine pit when the tail water level is high. Today, we will discuss several classifications of turbine seal from the structure of turbine main shaft seal.
The working seal of hydraulic turbine can be divided into
（1） Flat seal. The flat plate seal includes single-layer flat plate seal and double-layer flat plate seal. The single-layer flat plate seal mainly uses a single-layer rubber plate to form a seal with the end face of the stainless steel rotating ring fixed on the main shaft. It is sealed by water pressure. Its structure is simple, but the sealing effect is not as good as that of the double flat plate seal, and its service life is not as long as that of the double flat plate seal. The double-layer flat plate has good sealing effect, but its structure is complex and water leaks when lifting. At present, it is also used in small and medium-sized axial-flow units.
（2） Radial seal. Radial seal consists of several fan-shaped carbon blocks tightly pressed on the main shaft by springs in the steel fan-shaped blocks to form a layer of seal. A small drainage hole is opened in the sealing ring to discharge the leaked water. It is mainly sealed in clean water, and its wear resistance is poor in sediment containing water. The seal structure is complex, the installation and maintenance are difficult, the spring performance is not easy to ensure, and the radial self-regulation after friction is small, so it has been basically eliminated and replaced by the end face seal.
（3） Packing seal. Packing seal is composed of bottom seal ring, packing, water seal ring, water seal pipe and gland. It mainly plays a sealing role by the packing in the middle of the bottom seal ring and gland compression sleeve. The seal is widely used in small horizontal units.
（4） Face seal. Face seal * * * mechanical type and hydraulic type. Mechanical end face seal relies on the spring to pull up the disc equipped with circular rubber block, so that the circular rubber block is close to the stainless steel ring fixed on the main shaft to play a sealing role. The rubber sealing ring is fixed on the top cover (or support cover) of the hydraulic turbine. This kind of sealing structure is simple and easy to adjust, but the force of the spring is uneven, which is prone to eccentric clamping, wear and unstable sealing performance.
（5） Labyrinth ring seal. Labyrinth ring seal is a new type of seal in recent years. Its working principle is that a pump plate device is set on the top of the turbine runner. Due to the suction effect of the pump plate, the main shaft flange is always in the atmosphere. There is no contact between the shaft and the shaft seal, and there is only a layer of air. The seal has a very long service life. The main shaft seal is a non-contact labyrinth type, which is composed of a rotating sleeve close to the shaft, a sealing box, a main shaft seal drainage pipe and other components. Under the normal operation of the turbine, there is no water pressure on the sealing box within the whole load range. The pump plate on the runner rotates with the runner to prevent water and solids from entering the main shaft seal. At the same time, the drainage pipe of the pump plate prevents sand or solid substances from accumulating under the top cover of the water turbine, and discharges a small amount of water leakage through the upper leakage stop ring to the tail water through the drainage pipe of the pump plate.
These are the four main categories of turbine seals. In these four categories, labyrinth ring seal, as a new sealing technology, can effectively prevent water leakage on the sealing box, which has been adopted and used by many hydropower stations, and the operation effect is good.
Post time: Jan-24-2022
