Abstract: The pump comprises three distinct series of pumping stages driven on a single shaft by the same motor. Between the first and second series of pumping stages, the liquid is diverted from the pump through a by-pass towards, for example, a filtering device for removing the liquid as many impurities as possible. Then, the filtered liquid is conveyed back to the second series of pumping stages of the pump where the liquid is pumped at high pressure before being conveyed through a by-pass outside of the pump and towards a treatment chamber, such as a chamber for reverse osmosis, nanofiltration, or the like. The permeate (filtered solution) is removed from the installation whereas the solute (concentrated solution) is, in large part, reconveyed towards a third series of pumping stages, at the discharge of which the liquid is mixed with the filtered liquid from the second series of stages and the mixture is then conveyed again towards the treatment chamber. This high yield system eliminates a second and third pump.