The Dv12 (Sv12 and Sr12 until 1977) is the standard Finnish medium-weight diesel-hydraulic road switcher operated by VR. As all the main lines of Finnish railway network have been electrificied, the locomotive is designated mostly to unelectrified, less frequently used side lines. Occasionally it may still pull cargo trains on main lines. It has also been put in service as a shunter, replacing older classes Dv15 and Dv16 as they were retired. A total of 192 locomotives were built by Lokomo and Valmet between the years 1963 and 1984. As of 2025, the oldest Dv12 units still in use are 62 years old.
Technical information
The Dv12 is a general purpose locomotive which was designed for both passenger and cargo train use. Its 1000 kW power is somewhat low by current standards, but it is capable of multiple-unit operation with only one train crew and doublets and triplets are common. It has a low axle load of 15.6 tonnes, which makes it very well suited for branch lines that allow only smaller axle loads. All the axles are interconnected with shafts and universal joints to the Voith L 216 rs hydraulic transmission. Because all axles must rotate at the same speed, the individual slipping of axles is impossible. This translates into a very good tractive effort for a 62 tonne locomotive. The main engine is a Finnish-built Tampella SACM MGO V16 BSHR Diesel with two Brown Boveri-VTR 200 M turbochargers.
The Dv12 has two speed ranges, 85 km/h for cargo use and 125 km/h for passenger use. This mechanical gear can only be switched with the locomotive at standstill.