Renovating the dam gates at the Tainionkoski power plant demanded diverse and comprehensive reengineering skills
Unlike the other forms of energy, hydropower is pure regulating power and therefore perhaps even more important than its relative share in the electricity production in Finland. That is why maintaining and renovating old hydroelectric power plants and dams is important and makes good economic sense. Oulu-based OMP Works and ATA Gears together carried out the first phase of the renovation of the gates at both ends of the spillway channels during 2024-2025. ATA Gears supplied the large gear racks and wheels required for the gate opening mechanism.
It started with a blurry photo and a small cup of input data
“Hydropower is a challenging working environment. You have to acknowledge the basic principles,” says Jaakko Kotajärvi, Production Director at OMP Works. “When the drop height of the dam structure can be anything between 5 and 50 meters, so many different work beds and scaffoldings are built and careful account must always be taken of the risk of falling. Excavation and diving are involved – so perhaps not exactly standard work,” describes Kotajärvi, who led the project. Understanding the structure of the old dam gate brought its own challenges to the project, because after 75 years the original calculations were no longer available. “In addition, the old gate had already been melted down, so we first had to do a lot of detective work to determine the correct functional dimensions, basically based on a photo and decidedly inadequate input data.”
In addition to the project leader, OMP’s Tainionkoski team had its own people in charge of design, production and installation, and a variable number of people working on site, depending on the project phase. Regarding the gear components, OMP’s team worked closely with ATA’s designers. The gear wheels of the Tainionkoski roller gate were implemented as full semi-circles using modern involute gear profile instead of the old design based on straight tooth surfaces. The dam gate itself was completed in May 2025 and the gate lifting mechanism was installed during October-November.
With reverse engineering into an involute
Water flow is regulated by moving the floodgate vertically. The movement is achieved via rack/pinion components supplied by ATA at both ends of the floodgate. “The original racks/pinions were based on an approximately 100-year-old design, in which a gear sector of approximately 180°, divided into four parts, rolled against the rack,” says Jesse Rontu, Chief Gear Engineer responsible for the Tainionkoski project at ATA Gears, and continues: “Manufacturing technology has advanced since then, so the gear design of the Tainionkoski dam gates was rethought and designed from scratch. The old components had straight-sided, presumably cast, teeth, while the new design was based on involute tooth profile machined using modern methods. In addition, the gear wheels were manufactured as one-piece 180° sectors instead of a structure consisting of several parts. This made the manufacturing more cost-effective, the end result more precise, and the assembly simpler, because there are no additional connecting surfaces.”
In other words, the project went from a 100-year-old, cast, straight-toothed, four-part structure to a modern, machined, involute-toothed, single component: a great example of ATA Gears’ reverse engineering expertise.