A tuyau is a hydrostatic pressure mechanism used in ancient Roman forges to supply compressed air to operate machinery. It involves subsea pipes and a plenum chamber and was easy to install near streams. It changed the location of ironworking operations and allowed forges to be brought closer to water sources.
In French, tuyau means pipe or conduit. Literally therefore, a tuyau is almost any type of rigid or flexible pipe. More commonly, however, a tuyau refers to a specific hydrostatic pressure mechanism involving subsea pipes and a plenum chamber to supply compressed air to operate machinery. The mechanism was used as an early forge device by the Romans and significantly changed the way iron was worked in ancient times. Compression from a tuyau worked much like bellows in more modern forges.
Roman iron forges developed the device further over the centuries, with some forges featuring tuyaux with water hammers to work the molten iron ore. Because the device had no moving parts or wearable seals, it was easy to install near streams and other bodies of water. Deep water allowed the tuyau to produce higher compression and therefore more horsepower. Compressed air from a pipe-only water system is cool and surprisingly dry, even though it is derived from water.
As regards the specific construction, both ancient and modern tuyaux are equipped with a tube with internal nozzles, placed with one end facing upstream. The water flows into the tube as the nozzles help create more air bubbles in the incoming water. The rising water inside the pipe causes the pipe to sink deeper into the water, thus increasing the hydrostatic pressure. Gravity, water depth, and water temperature all determine the amount of pressure produced during this process.
At the opposite end of the tube, a small plenum attracts air bubbles and forces the water to flow sideways. Higher hydrostatic pressure increases the number of air bubbles pushed into the filling chamber. Air bubbles within the plenum burst due to pressure changes, providing compressed air that can be fed through another tube to power forges, water hammers, and other mechanisms. Once the air bubbles burst, the hydrostatic pressure in the tuyau decreases, the tube rises, and the process repeats.
The decrease in hydrostatic pressure combined with the release of compressed air supplies the necessary water discharge during the final processing stage of a tuyau system. The pipes rise out of the water as the pressure drops, in order to pump water into the stream. Each step in the process repeats and overlaps, providing a constant supply of compressed air. While constant in terms of delivery, the force or pressure of compressed air delivery is not always that consistent.
The use of a tuyau system helped change the location of ironworking operations in Roman times. Rather than focusing on fire supplies and then locating forges near forest or coal supplies, operations could instead focus on power generation. Understandably, the forges were thus brought closer to streams and other bodies of water with a good current to take advantage of falling water systems such as a tuyau. Many improvements over the centuries have come from modifying the water supply systems used in mills and other industries.
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