Channel Tunnel Engineer examines a Piston Relief Duct (PRD) - used for controlling air pressure - in a French rail tunnel.
When a train passes along a close-fitting tunnel, air pressure builds up in front of the train which eventually affects economy and passenger comfort. In a land-based tunnel, this air is usually allowed to escape to the surface through special air ducts but, under the sea, this isn't possible. The Eurotunnel system ingeniously allows this air pressure build-up to escape into the opposite rail tunnel through a series of 2m diameter piston relief ducts situated every 250m and looping over the service tunnel.
Size: 4157px × 4130px
Location: 40m under seabed between UK and France, Europe
Photo credit: © qaphotos.com / Alamy / Afripics
License: Licensed
Model Released: No
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