Hydro-turbines are critical to converting water’s mechanical energy into electricity, and a crucial component within these massive systems is the main shaft axial seal. The primary function of this seal is to control the flow of water around the rotating shaft. While in theory, a perfectly sealed system would eliminate leakage, this is not economically feasible for large-scale turbines. The design priority is therefore to limit leakage to an acceptable level, balancing cost with performance. 

In contrast, axial seals, also known as mechanical or face seals, are better suited for high-pressure, large-scale applications. The key innovation in recent years has been the use of elastomeric polymer materials, such as Thordon SXL, to replace traditional carbon-based seals. Elastomeric polymers offer several advantages: they are non-brittle, highly resistant to abrasion, and provide a longer service life in abrasive environments. Moreover, they are more economical and easier to manufacture in large sizes compared to carbon. 

The principle behind axial turbine shaft seals lies in managing leakage while maintaining mechanical stability. In small systems, the sealing surfaces are machined to extreme flatness, but this is impossible for large hydro-turbines. Instead of aiming for microscopic flatness, axial seals for turbines feature macroscopic waves on the sealing surface. This undulation helps create a hydrodynamic film, reducing friction but allowing some leakage. As the turbine operates, the sealing surfaces undergo “commissioning wear,” where they gradually flatten and develop into continuous contact surfaces over time. 

Although leakage cannot be entirely prevented, with careful design and material selection, elastomeric polymer axial seals can control leakage within acceptable limits. Records show leakage rates can be achieved from 10 to 90 L/min depending on shaft size, turbine pressure, and operating conditions. 

As we’ve explored, the design and functionality of hydro-turbine axial seals are critical for controlling leakage and ensuring efficient operation. However, while understanding the principles behind these seals is important, the real value comes from choosing the right materials to meet the demands of large-scale turbines.

In the next post, we’ll dive deeper into the advantages of using elastomeric polymer seals, particularly the innovative Thordon SXL, and how this material is transforming turbine performance. Stay tuned to discover why elastomeric polymers are becoming the go-to solution for modern hydro-turbine systems!