March 18th, 2019

TS Malter - Valve replacement in the diversion tunnel

Dam gate valve during the pressure test at the manufacturer's premises

At the listed Malter Dam, an Intze gravity dam made of quarry stones (construction period 1908-1913, height 36 m, total volume 8. 78 million m³) at the Rote Weißeritz in Saxony, the extreme flooding of 2002 caused a significant hydraulic overload of the operating facilities due to the exceeding of the then valid BHQ 2. 

The values for BHQ 1 and 2 newly determined after 2002 with an N-A model have now risen sharply with regard to peak values and discharge fills, so that the flood safety of the shut-off structure could no longer be demonstrated and the operating facilities have to be extended taking into account the existing plant stock. In addition to the expansion of HWE, the focus was also on increasing the hydraulic performance of the valves in the diversion tunnel. Previously, two butterfly valves with downstream throttle orifice plates were fitted in each of the three pipe sections. This meant that the maximum allowable discharge without damage in the underflow (40 m³/s) could not be exhausted for the pre-relief and cavitation problems arose. 

On behalf of the operator (LTV Sachsen), the existing deficits were therefore eliminated between 2014 and 2018 with the planning and installation of dam gate valves (TSS) in closed design (sliding gate in pressure housing as welded construction made of stainless steel) specially designed for this purpose and location. The installation of the six new TSS was carried out under complicated boundary conditions in the basement of the approx. 31 m deep slide shaft. Two TSS with square flow cross-sections of 1,000 mm x 1,000 mm and controllable disc ventilation valves DN 500, which can be operated up to v = 17 m/s (with ZK) with low vibration, are used for each pipe string. The hydraulic capacity per pipe string is Q approx. 15. 8 m³/s at ZV. The TSS pairs stand in strands on new approx. 60 cm high reinforced concrete foundations and are connected vertically via prestressed threaded rods M27 10. 9. The foundations transfer the horizontal forces occurring with closed TSS and the offset torque into the subsoil via one shear dowel and one continuous tensile pile each ∅ 50 GEWI. The TSS were equipped with hydraulic actuators according to DIN 19704 mounted directly on the slide pressure covers and have a piston rod integrated displacement measuring system with programmable end positions (operating time 1. 0 min/stroke). 

The corrosion protection was renewed in the embedded seal pipes before and after the pipe cellar. The valve replacement is also an important prerequisite for the construction measures planned from summer 2019 for the expansion of HWE. 

Dr. Holger Haufe, Martin Stärker - Dresden