Trompe

A trompe is a water-powered air compressor, commonly used before the advent of the electric-powered compressor. A trompe is somewhat like an airlift pump working in reverse. Trompes were used to provide compressed air for bloomery furnaces in Catalonia and the USA. The presence of a trompe is a signature attribute of a Catalan forge, a type of bloomery furnace. Trompes can be enormous. At Canadian Hydro Developers' Ragged Chute facility in New Liskeard, Ontario, water falls down a shaft deep and across to generate compressed air for mining equipment and ventilation. Trompes are very simple devices. They consist of four main parts: water-supply pipe or shaft with an air-inlet inside it, water outflow pipe, separation chamber and takeoff air-pipe. The vertical pipe or shaft goes down from higher point to a separation chamber; a pipe, that is typically narrower than previous one, coming away from that chamber, allows the water to exit at a lower level, and another pipe (air-pipe) coming from the chamber allows the compressed air to exit as needed. Water rushing down the vertical pipe falls through a constriction. The constriction produces a lower pressure because of the venturi effect, and an external port allows air to be sucked in thus creating a constant air supply. The air forms bubbles in the pipe. As the bubbles go down the pipe they are pressurized proportionally to the hydraulic head, which is the height of the column of water in the pipe. The compressed air rises to the top of the separation chamber (wind box). The separation chamber has a compressed-air takeoff pipe, and the compressed air can be used as a power source. The energy of the falling water creates a partial vacuum inside the pipe that is compensated by the air from the outside atmosphere provided through inlet. The air is compressed by surrounding water pressure (which increases under a column due to the discharge to atmospheric pressure). The pressure of the air delivered cannot exceed the hydraulic head of the discharge pipe of the separation chamber.