Volumetric pressure exchanger for a seawater desalination plant and desalination plant

A volumetric pressure exchanger comprising

• at least one pressure exchange unit,
• wherein said pressure exchange unit comprises a hollow cylindrical body, a piston sliding in said body, said piston comprising a piston head separating the inside of said cylindrical body into a downstream chamber and an upstream chamber, said piston comprising a rod fixed to said piston head, arranged on the side of the downstream chamber and crossing through said downstream chamber, said downstream chamber being provided with an intake and discharge device for water to be treated, said upstream chamber being provided with a three-way valve with a rotary gate, said rotary gate being rotated by motorized driving means, said gate comprising an orifice for supplying a pressurized concentrate, an orifice for discharging said concentrate, and an opening for communicating with said upstream chamber, wherein the volumetric pressure exchanger is configured to not mix the water to be treated with the pressurized concentrate, and wherein the speed of rotation of the gate is adjusted such that the piston does not reach an upper end of travel, so that the volumetric pressure exchanger is made self-adapted to an incoming flow rate.