World's first 500MW impulse turbine ball valve passes pressure test in Tibet

There’s a quiet engineering race unfolding in the mountains of Tibet, and China just hit a milestone worth watching.

Dongfang Electric has completed on-site assembly and pressure testing of the world’s first 500-megawatt impulse turbine ball valve at the Dacha (Zala) hydropower station. The valve, the inlet gate for Unit 1, passed hydrostatic pressure tests across all operating conditions, meeting design requirements for sealing performance.

The Dacha station sits at high altitude under extreme conditions — high water head, massive capacity, thin air. It will house two 500MW impulse turbine units, with Dongfang Electric supplying one complete set. The ball valve itself is a piece of heavy machinery: 2.9-meter bore diameter, 9 megapascals design pressure, over 300 tons assembled weight. It’s built from a large and small valve half, a rotating plug (the “活门” or moving gate), and valve shafts.

Assembling something this size in a remote mountain site is not straightforward. The project team developed a “four-point positioning” method specifically for the valve’s oversized dimensions, solving what they describe as an industry-wide headache: aligning the valve shaft with the shaft bore while maintaining concentricity within precision-grade tolerances. The technique worked well enough to meet all design specs.

The project is listed under China’s National Energy Administration as a first-set major technical equipment initiative. It’s currently the only domestic project capable of developing and demonstrating 500MW-class, high-head impulse turbines — and by most accounts, it’s the most technically challenging impulse hydro project under construction anywhere in the world.

The photo released by Dongfang Electric shows the completed assembly on the project site.