Abstract: A pressure vessel designed to hold a plurality of cylindrical cartridges in the form of cross-flow semipermeable membrane filtration elements having central permeate tubes that are interconnected to form a composite permeate passageway that extends axially of the pressure vessel. Several constructions are shown for compensating for assembly clearance and potential pressure vessel growth and uniquely biasing the column of cartridges towards the downstream end of the pressure vessel to prevent axial shuttling movement that could cause wear and deterioration of seals which would result in leakage and deterioration of product while providing for absorption of shock potentially promulgated from the downstream end should feed pressure be suddenly lost.

Abstract: Apparatus and methods for producing potable water from an aqueous feed such as seawater utilizing a pressure vessel designed for operation in the range of about 250 psig to about 350 psig having reverse osmosis (RO) separation elements disposed upstream of at least one nanofiltrate separation element. The supply of seawater at such pressure creates no permeate flow through the RO membranes, so the seawater flushes the feed side of the RO elements on its way to the NF element where very substantial permeate flux occurs, producing a NF permeate substantially depleted in divalent ions and optionally moderately depleted in monovalent ions. The NF permeate is collected in a holding tank having liquid level switches, and when a desired level is reached, a control system causes the pump to draw suction from the holding tank while shutting off feed from the seawater source.

Abstract: Water from a source is fed to a reverse osmosis unit having a membrane which divides the stream into a first permeate product and a first concentrate. The first permeate product is stored in a tank until a selected quantity is collected and then the source is disconnected from the pump which next delivers water from the tank to the reverse osmosis unit to divide the stream into a second permeate product and a second concentrate. In one version of the equipment the second permeate is processed by a different membrane than that producing the first permeate. In another version, the same membrane is used, the second permeate product is stored, and the second permeate product is later run through the reverse osmosis unit to produce a third permeate product and a third concentrate.