Probably you are all familiar with the Feifel air filtration system on early Tiger tank. Tiger 131 from the Tank museum, sport this system and as part of it, it has air filtration units mounted on either side of the rear. The air filtration units suck in air using ducts placed on the engine deck. A pair of ducts is used to get air to the filtration unit and back to the engine, where the clean air is used to supply the engine. The ducts themselves have an iconic angular shape to them.
To my surprise these ducts aren’t unique to the Tiger at all. I found the same type of duct used in another air filtration solution, as commonly used in German bunkers. In the images below you see this type of duct used on a Heeres Einheits Schutzlüfter (HES) air filtration device. This device is able to pull air trough different types of air filters – the devices pictured below have a rating of 1,2 m³ air per minute. The HES could either be hand cranked or be driven by an electric motor mounted on the underside of the device.
The bunker complex at Bunkermuseum Kornwederzand, The Netherlands encompasses a few German built bunkers where I spotted this system. The ducts themselves are not very flexible at all and are quite hard to bend into a given direction due to the friction between the individual links.