A trompe is a water-powered gas 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.
In Paris they were used for a time to compress air to drive the city's first electricity generation scheme, and in the Alps they were used in France and Switzerland to provide compressed air for early alpine tunnels.
Trompes can be enormous. At Canadian Hydro Developers' Ragged Chute facility in New Liskeard, Ontario, water falls down a shaft 351 feet (107 m) deep and 9 ft (2.7 m) across to generate compressed air for mining equipment and ventilation.
Trompes are very simple devices. A vertical pipe or shaft goes down to a separation chamber, a pipe coming away from that chamber allows the water to exit at a lower level, and another pipe coming from the chamber allows the compressed air to exit as needed.