Of simple and robust construction, these pumps of the volumetric type are autonomous and can use all gases under pressure compatible with the process like driving fluid. Specifically conceived for the transfer of the liquids, under pressure or vacuum close relations of their vapor tension (such as, for example, steam condensates), they remove any risk of cavitation and are thus practically without maintenance. Without electric energy need, they are particularly adapted to dangerous or wet environments. These pumps are available, according to the models, out of cast iron, steel or stainless steel and cover a beach of flows from 0 to 30 m3/heure.