When researching applied sealing, theoretical analysis and calculation have been carried out repeatedly to form a calculation program, and the result is that this program conforms to the calculation results provided by the sealing material out-sourcing manufacturer. The establishment of the calculation judgment standard can facilitate the sealing structure design and the size confirmation of the sealing block.
Combined Sealing: In order to better guarantee the sealing performance of the main shaft, in the actual design, we often adopt a variety of forms of sealing, that is, combined sealing. There are several combined sealing structures, such as "hydraulic pressure end face sealing + oblique sealing" structure, "pump plate sealing + non-contact clearance sealing" structure, "broach + flat-plate main shaft sealing" structure and so on.
Pump plate sealing + non-contact clearance sealing: This kind of combined sealing structure can be used in the main shaft seal design of mixed-flow turbine with high head and high speed. This sealing is very effective because the upper pump plate of the runner can reduce the amount of water passing through the non-contact clearance to very little or even none, so there is almost no wear in the non-contact seal.
Working Principles of “Pump plate sealing + non-contact clearance sealing”: When the turbine functions properly, the pump plate installed on the wheel rotates together with the wheel. Because of the high rotation speed, the centrifugal effect generated by the rotation and the stirring of the pump plate throws off the water outward, which makes the water on the top stop leakage ring discharged through the pressure relief tube arranged on the top cover. And the water pressure before the main shaft seal is reduced and the amount of water is reduced. The sediment or solid matter is effectively prevented from depositing under the top of the water engine, so that the main shaft is sealed without contacting with the sand and other solid substances in the water, thus effectively preventing the sediment from entering the main shaft seal and reducing the leakage. When the turbine is shut down, the water is sealed through the static seal (that is, the maintenance seal) installed under the sealing box, and the small amount of leakage of the wheel can be discharged through the main shaft sealing drainage pipe.