Abstract: A novel control for use with a reverse osmotic treatment system is disclosed. The unit (9) provides the desired flow of product solution from the system by controlling a "single" valve (3) disposed on a secondary line for conveying a concentrated solution coming out of a reverse osmotic apparatus (4). One application of this control unit is in desalination of salt water. Once the desired level of the flow of desalinated water (Q.sub.1) is initially set, the control unit (9) determines automatically the necessary opening (A.sub.v) of the valve in accordance with the performance characteristics (21 to 28) of the components of the desalination system [centrifugal pump (1), reverse osmotic apparatus (4) and the system line]. In response to this determination, the valve develops the desired pressure at the inlet of the reverse osmotic apparatus (4), which then produces desalinated water at a flow rate substantially equal to the initially set value (Q.sub.1).

Abstract: This invention relates to a membrane separator which separates matters with a semipermeable membrane to obtain a dilute solution or a concentrated solution or both. In such a membrane separator, the most economical operation is attained by the condition in which the maximum amount of the desired solution is obtained by the minimum energy, that is, the required energy per unit amount of the solution obtained. Heretofore, the minimum power has been sought at the maximum pressure corresponding to the performance of the semipermeable membrane with the result that the required energy could not be minimized.