Pump and a desalination system including the pump

A desalination system for desalinating sea water, the system including a supply pump drawing a supply of raw sea water, a filter receiving raw feed water from the supply pump, a feed pump receiving filtered sea water from the filter, a membrane unit receiving filtered sea water at high pressure from the feed pump, and discharging fresh water at one outlet and a high pressure concentrate at another outlet, the feed pump receiving the high pressure concentrate, applying energy from the high pressure concentrate to pumping the filtered sea water, and discharging lower pressure concentrate, the feed pump comprising:

• four cylinders, a double acting piston in each cylinder, thereby defining a feed chamber and a recovery chamber, all connected to a common drive by a connection, wherein there is no lost motion mechanism associated with each piston, the connection to the common drive being such that the pistons reciprocate in a sequence equally spaced in time, valving for each piston driven by the common drive to be 90 degrees out of phase with the respective piston, the valving being such as to connect the recovery chamber alternately to an inlet manifold for an intake stroke of the piston relative to the recovery chamber, and to an outlet manifold for a discharge stroke of the piston relative to the recovery chamber, with a brief period of closure coinciding with top dead centre and bottom dead centre of the piston, during which the recovery chamber is blocked off from both the inlet and outlet manifolds, the valving being midway between its top dead centre and bottom dead centre during the period of closure.