Swiss Federal Railways: servicing of the Eau Noire water intake

Swiss Federal Railways (CFF) asked us to service the Eau Noire water intake, an integral part of the Emosson complex. They gave us a comprehensive commission, including on-site disassembly, servicing in our workshops, and reassembly on the site of the plant, all with a relatively tight deadline.

The construction of the Vernayaz hydroelectric power plant between 1924 and 1927 followed the commissioning of the first turbines at Châtelard, fed by water from the Barberine dam.  To increase production in summer, river water intakes were constructed at Trient and in the place known as Eau Noire, close to the French border. 

The Eau Noire intake, constructed in 1925 by Ateliers Mécaniques (engineering workshops) of Vevey, comprises three stop logs (A-B-C) driven by rack and pinion. The Operator’s observations showed that the stop log seals were no longer fully watertight, leading to water losses, and that stop log A was often sticking in its slides.

In the autumn of 2018, major consolidation works on the right bank required the plant to temporarily cease operation, enabling  the operator to plan servicing of the stop logs.   CFF gave us a comprehensive commission, including on- site disassembly, service in our workshops, and reassembly on the site of the plant, all with a relatively tight deadline.

Their technical specifications for the service provided for the following works:

  • Supply and replacement of the six slides,
  • Machining of stop log A to improve its movement in the slides,
  • Non-destructive testing of the stop logs,
  • Complete renewal of the anti-corrosion protection,
  • Supply and replacement of wooden seals and rubber joints.

Observations with the client in the workshop after complete disassembly identified deterioration of the stop logs that was much more serious than expected. By agreement with CFF we undertook additional work to ensure optimal future operation of the plant:

  • Servicing of the rack and pinion drives,
  • Servicing of the fixed mountings of the stop logs,
  • Reinforcement and repair of the stop logs by welding.

Following the action in the workshop, our assembly team carried out reassembly of the serviced stop logs within the client’s deadlines The geographical proximity of our workshops and our excellent working relationships enabled CFF’s technicians to take rapid decisions, so as not to miss the deadline for the return to operation, which was essential in this project.

Vernayaz power plant

  • 3 horizontal twin-jet Pelton turbine sets
  • First commissioned in 1928, restored in 1974 and 1989
  • Height of fall 645m
  • Flow 17 m3/s
  • Speed of rotation 501 min-1 
  • Power 92 MW



HYDRO Exploitation SA
Rue de l’Industrie 10
CP 315 - CH-1951 Sion
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HYDRO Exploitation SA
Rue de l’Industrie 10 CP 750 - CH-1951 Sion +41 (0)27 328 44 11
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