Pile-driving is like hammering nails into wood. Except the nails are 30cm or even metres in diameter and 10 or 50m long, and the wood is the Earth! Once in the ground, piles are joined together and form the foundations of buildings from skyscrapers to wind turbines. There are other ways, but a lot of piles are put in the ground by a falling weight. The weight – the hammer – is simply hauled up and then let drop. Here is how to make a pile-driver run off a vacuum cleaner that can hammer garden stakes and posts into the ground.
A mains vacuum cleaner can put out about 200mbar pressure – 20 per cent of atmospheric pressure – and a flow rate of tens of litres/second. With this kind of power, up to ~10kg force on an 8cm pipe, a wooden hammer-piston of a few kilograms can easily be sucked up a vertical pipe. A big chunk of wood, circular or with circular rings which fit the pipe to within a millimetre or so, makes a...