Reverse osmosis method and apparatus

A pumping apparatus for a membrane separation apparatus for separation of a feed fluid into permeate fluid and concentrate fluid fractions which respectively are permeated and rejected by selective membrane means, the pumping apparatus being characterized by:

• (a) a reciprocating pump means having a cylinder and moveable piston means, the piston means dividing the cylinder into a pumping chamber in which the feed fluid is pressurized and an expansion chamber in which the concentrate fluid fraction is depressurized, the piston means cooperating with piston rod means extending through the expansion chamber with sealing means to prevent leakage of fluid from the cylinder, the cylinder and piston rod means having relative diameters which define cylinder/piston rod proportions such that ratio of swept volume of piston rod means to swept volume of the piston means determines recovery ratio of permeate fluid fraction to total feed fluid flow,
• (b) inlet conduit means communicating with the pumping chamber to admit feed fluid into the pumping chamber,
• (c) outfeed conduit means adapted to communicate the pumping chamber with the membranes so as to conduct pressurized feed fluid from the pumping chamber to the membranes,
• (d) return conduit means adapted to communicate the membranes with the expansion chamber so as to conduct the concentrate fluid fraction from the membranes to the expansion chamber,
• (e) means communicating with the outlet and return conduit means to reduce fluctuations in pressure and feed fluid flow across the membrane means,
• (f) first and second valve means, the first valve means communicating with the expansion chamber and having a closed intermediate position between first and second positions, the second valve means being non-return valve means communicating with the pumping chamber, the first and second valve means cooperating with the conduit means so as to direct fluid flow from a feed fluid source and to and from the membrane means,
• (g) reciprocable mechanical drive means mechanically connected to the pump means and the first valve means so that the first valve means is responsive to force applying the reciprocation action to the pump means in such a manner that reciprocating force transmitted to the pump means is reacted in part by the first valve means such that reversal of force reverses the valve means,
• (h) dwell means associated with the pump means to ensure that the first valve means is shifted during an interval of substantially zero fluid transfer in the expansion chamber, the dwell means being characterized by a hydraulic bias effect acting on the piston means to inhibit relative motion of the piston means in one direction as determined by the position of the first valve means and to permit relative piston motion in the opposite direction, such that following reversal of force applied to the pump means, the first valve means shifts between the first and second positions thereof prior to reversal of pumping action,
• so that in a first position of the first valve means pressurized feed fluid from the pumping chamber is fed to the membranes through the second valve means while concentrate fluid is discharged into the expansion chamber through the first valve means, so that depressurization of the concentrate fluid returning from the membrane means assists in pressurizing of the feed fluid, and in a second position of the first valve means depressurized concentrate fluid is exhausted from the expansion chamber through the first valve means while feed fluid is inducted into the pumping chamber through the second valve means.