Water purification by reverse osmosis

An apparatus for the reverse osmosis purification of water under high pressure comprising:

• (a) an elongated housing of the same cross-sectional size throughout its length and having a closed front end and a closed rear end;
• (b) a piston-like movable partition disposed transversely in the housing and separating the housing into two separate and non-communicating chambers, said partition having a front face and a rear face;
• (c) an actuating rod having an inner end portion connected to the rear face of the movable partition with the rod extending therefrom to the rear end of the housing and having an outer end portion sealingly slidably disposed through the rear end of the housing and power drive means operatively connected to the outer end portion for reciprocably moving the partition in the housing between the ends thereof;
• (d) said front face of the partition facing the front end of the housing and defining therewith a variable feed liquid chamber;
• (e) inlet means communicated with the feed chamber for supplying a supply of liquid, such as seawater, to the feed chamber;
• (f) valve means for said inlet means to prevent the return of supply liquid therethrough from the feed liquid chamber;
• (g) a reverse osmosis module comprising a housing divided by a semipermeable osmostic membrane, a separate liquid inlet and outlet in the housing on one side of the membrane and an outlet for fresh water in said housing on the other side of the membrane;
• (h) outlet means from the feed chamber separate from the inlet means and connected to the liquid inlet for the osmosis module housing;
• (i) valve means for said outlet means to prevent the return of liquid from the osmosis module housing to the feed chamber;
• (j) said rear face of the partition facing the rear end of the housing and defining therewith a variable return liquid chamber;
• (k) said partition being moved by the power drive means with the opposite faces thereof being under high liquid pressure and with substantially the same pressure existing on the opposite faces of the partition;
• (l) the rear face of the partition being of a cross-sectional area less than that of the front face to the extent of the cross-sectional area of the actuating rod with the ratio of such cross-sectional area of the actuating rod to the front face of the partition being substantially the same as the extraction ratio of the purified water to the supply liquid entering the feed liquid chamber and with said areas of said faces of the partition being in accordance with the extraction ratio so as to avoid a pressure difference across the partition.
• (m) a liquid connection between the outlet in the osmosis module housing and the return liquid chamber and communicating said outlet with the return liquid chamber so that return from the osmosis module housing is applied to the rear face of the partition;
• (n) first valve means allowing the flow of the return liquid from said outlet into the return liquid chamber as the partition is moved by the actuating rod toward the front end of the housing to force the supply liquid into the osmosis module housing;
• (o) outlet means from the return liquid chamber for the discharge therefrom of return liquid;
• (p) second valve means allowing the flow of the return liquid through said outlet means as the partition is moved rearwardly in the housing and supply liquid enters the feed chamber;
• and,
• (q) control means controlling the alternate opening and closing of the first and second valve means in accordance with the movement of the partition toward the ends of the housing whereby the partition circulates the supply liquid through the osmosis module housing on each forward stroke, with the high pressure being approximately balanced on opposite faces of the partition throughout the operating movements of the partition, and on the return stroke draws fresh supply liquid into the feed chamber and passes the return liquid from the return chamber thus ensuring that the pressures on the opposite faces of the partition are substantially balanced.