Compressed air storage tank (reservoir, wet tank), a cylindrical high-pressure reservoir of the air brake system for road vehicles. The compressed air brake system of heavy trucks, buses, tractors and other commercial vehicles consists of parking brakes, service brakes, a control pedal, and air storage tanks. The parking brakes are applied by spring pressure, and air pressure is required to release them. When the engine is running, a compressor produces compressed air, filling the air reservoir and releasing the parking brakes. When the brake pedal is pushed, compressed air is routed to the service brakes, causing the brake drums or discs to be engaged. Any air pressure lost in the process, is restored by the compressor drawing filtered air from the atmosphere and forcing it into the air storage tank. A sudden loss of air pressure will cause the parking brakes to engage and emergency brake the vehicle. Truck drivers are instructed to downshift and use the engine brake downhill to maintain sufficient air pressure in the air brake. Spectacular accidents and runaway truck ramps with gravel traps are a constant reminder of the importance of downshifting.
The used ROCO 1:87 scale model of the German Faun 10 ton artillery tractor pictured above was sold without the compressed air storage tanks on the left side of the vehicle. The original part has two rectangular connectors which fit into sockets beneath the truck bed of the Faun L 908/425 A. This plug-and-play connection is quite good, but it will not hold the part in place forever. Once MiniTanks' small parts land on the floor they are only too eager to disappear in a vacuum cleaner. The replacement part, which looks more realistic than the original, is easily scratch-built from 2 mm and 2.5 mm polystyrene rod with supports made of 0,25 mm polystyrene sheet taken from a yoghurt cup and small rectangular pieces of scrap plastic sprue.