Proposed is a pump assembly designed to generate pressure for an incompressible-fluid consumer unit in which the resistance to fluid flow can vary, in particular for supplying the reverse-osmosis membrane of a sea-water desalination plant. The assembly includes a high-pressure pump (1) with a low-pressure pump connected in series with it on the aspiration side. The invention calls for the low-pressure pump to be a jet pump (7') whose driving-jet inlet is connected to the pressure side of the high-pressure pump by a line (9) and a tee-junction (11). The assembly includes at least one pressure-control valve (14, 17).
