Liquid treatment apparatus for filtering liquid under pressure
TECHNICAL FIELD 
     This invention relates to apparatus for providing a flow of pressurized liquid. The apparatus has particular application to the filtering of pressurized liquid to separate the pressurized liquid into a permeate portion and a concentrate portion and may be utilized for the desalinization of sea water. 
     BACKGROUND ART 
     My U.S. Pat. No. 5,482,441, issued Jan. 9, 1996, discloses a system which can be utilized to desalinate sea water. There are, of course, many prior art systems which utilize reverse osmosis to accomplish such objective. Typically, prior art desalinization systems are very expensive to operate and difficult to service. The system of my above-referenced patent addresses this problem. 
     The apparatus disclosed and claimed herein represents another approach to solving the problems inherent in the prior art and has certain features in common with the invention disclosed in my U.S. Pat. No. 5,462,414 including use of a reversible piston which cooperates with filter means to produce desalinated water. 
     While reversible pistons per se are employed in prior art hydraulic circuits generally, the structural combination of a reversible piston and other related mechanism employed in the present filtering system differs in regard to both structure and manner of operation. U.S. Pat. No. 4,793,153, issued Dec. 27, 1988 discloses a typical prior art hydraulic circuit employing a reversible piston to accomplish &#34;energy recovery&#34; in a mixed-phase motor in a refrigeration system. 
     DISCLOSURE OF INVENTION 
     The apparatus of the present invention provides a highly efficient, relatively low-cost approach for desalinization of sea water or for other operations wherein it is desired to filter a liquid under intensified pressure conditions. The apparatus employs a minimal number of seals and can be powered by liquid under low pressure, such as that produced by a conventional low pressure pump. 
     The present apparatus employs a minimal number of operating parts which cooperate to substantially increase the pressure of the liquid as compared to the pressure thereof when introduced into the apparatus or system. High pressures can readily be developed with the present invention, thus making it ideal for cross-flow filtration applications, including reverse osmosis filtration systems, wherein high pressures are necessary. 
     The liquid filtering apparatus of the present invention is for providing a flow of pressurized liquid and includes a hydraulic cylinder defining a cylinder interior. 
     A divider divides the cylinder interior into first and second compartments. 
     A first piston head is within the cylinder interior, the first piston head being movably mounted in the first compartment and forming a liquid-tight seal with the hydraulic cylinder to subdivide the first compartment to a first set of two subcompartments, said subcompartments of the first set of two subcompartments located at opposed sides of the first piston head. 
     A second piston head is within the cylinder interior spaced from the first piston head, the second piston head being movably mounted in the second compartment and forming a liquid-tight seal with the hydraulic cylinder to divide the second compartment into a second set of two subcompartments, said subcompartments of the second set of two subcompartments located at opposed sides of the second piston head. 
     A double-ended ram member is movably mounted within the cylinder interior and extends between the first piston head and the second piston head. A first end of the ram member is connected to the first piston head within a single subcompartment of the first set of two subcompartments and a second end of the ram member is connected to the second piston head within a single subcompartment of the second set of subcompartments. The ram member extends through the divider, is movable relative to the divider, and forms a fluid-tight seal with the divider. 
     The apparatus also includes first liquid flow path defining means defining a first liquid flow path extending between the two subcompartments of the first set of two subcompartments. 
     Second liquid flow path defining means defines a second liquid flow path extending between the two subcompartments of the second set of two subcompartments. 
     Pressurized liquid delivery means is provided having an outlet for pressurized liquid. Control means alternately introduces pressurized liquid from the pressurized liquid delivery means outlet into the first and second compartments to cause reciprocal movement of the piston heads and ram member within the cylinder interior and pressurization and flow of liquid through the liquid flow paths from the subcompartments of the sets of two subcompartments not accommodating a ram member end to their respective subcompartments accommodating a ram member end. 
     Liquid exit flow path defining means defines a liquid exit path communicating with the liquid flow paths for discharging excess pressurized liquid from the subcompartments not accommodating a ram member and not entering the subcompartments accommodating a ram member end. 
     Filter means is operatively associated with the first and second liquid flow path defining means for receiving pressurized liquid from the first and second liquid flow paths and filtering the pressurized liquid. 
     Other features, advantages, and objects of the present invention will become apparent with reference to the following description and accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a schematic view illustrating an embodiment of apparatus constructed in accordance with the teachings of the present invention incorporating a filter, the embodiment shown during one stage of operation thereof; and 
     FIG. 2 is a view similar to FIG. 1 but illustrating the apparatus embodiment during another stage of operation; and 
    
    
     MODES FOR CARRYING OUT THE INVENTION 
     Referring now to FIGS. 1 and 2, apparatus constructed in accordance with the teachings of the present invention includes a hydraulic cylinder 10 defining a cylinder interior 12. A divider 14 is disposed within the cylinder interior and divides the cylinder interior into first compartment 16 and second compartment 18. 
     A first piston head 20 is movably mounted in the first compartment 16 and subdivides the first compartment into a first set of two subcompartments 22, 24 located at opposed sides of the first piston head 20. A seal 26 is disposed about first piston head 20 to maintain a fluid-tight seal with the hydraulic cylinder. 
     A second piston head 30 having a seal 32 thereabout is movably mounted in second compartment 18 forming a liquid-tight seal with the hydraulic cylinder and dividing the second compartment into a second set of two subcompartments 36, 38. Subcompartments 36, 38 are located at opposed sides of the second piston head 30. 
     A double-ended ram member 40 is movably mounted within the cylinder interior and located between piston heads 20, 30. One end 42 of the ram member is connected to the first piston head within subcompartment 22. The other end 44 of the ram member is connected to the second piston head 30 within subcompartment 36. 
     The ram member 40 extends through divider 14, is reciprocally movable relative to the divider, and forms a fluid-tight seal with the divider. An O-ring 46 is illustrated for such latter purpose. 
     A conduit or flow line 50 defines a liquid flow path extending between subcompartments 22 and 24. A conduit or flow line 52 extends between subcompartments 56 and 58. 
     A pump 54 has an outlet 56 communicating with flow lines 58, 60, the pump pumping liquid from a source or supply thereof 62. The liquid may, for example, be sea water. Flow lines 58, 60 communicate respectively with flow lines 50, 52 through check valves 64 and 66. Check valves 68, 70 are disposed in flow lines 50, 52, respectively, as illustrated. 
     Flow lines 50 and 52 converge at a common flow line 72 leading to the input of a reverse osmosis filter 74 which may be of any suitable well known construction. Reverse osmosis filter 74 will serve to separate out a permeate portion in the form of fresh water if the sea water introduced thereinto is pressurized to a certain extent. Arrow 76 in the drawings indicates the flow of a permeate or product portion out of the filter. 
     The remaining portion, the concentrate or brine portion, flows through a conduit 78 and thence through a retrack valve 80. A segment of flow line 50 between retrack valve 80 and cylinder 10 delivers the concentrate or brine portion to the subcompartment 24 as indicated by the arrows. 
     The positioning of retrack valve 80 is determined by the positioning of an associated pilot valve 82. In FIG. 1, both the retrack valve 80 and pilot valve 82 are in their respective right-most positions wherein pressurized liquid from pump 54 will pass from line or conduit 58 through pilot valve 82 and thence through a conduit 84 to the left end of retrack valve 80. 
     Also with reference to FIG. 1, the pressurized liquid from pump 54 will displace check valve 66 and pass into subcompartment 38 as indicated by the arrows. This will cause a build-up of liquid pressure in the subcompartment 38 urging second piston head 30 to the left as shown in FIG. 1. The second piston head will cause the ram member 40 to move left along with first piston head 20 at end 42 of the ram member. 
     Piston head 20 will cause displacement of liquid in first compartment 16 into flow line or conduit 50 and displacement of check valve 68. 
     The liquid displaced from first compartment 16 will then enter filter 74 with a portion thereof passing as previously described through conduit 78 and retrack valve 80 into subcompartment 24. It will be appreciated, however, that not all of the liquid displaced from subcompartment 22 will enter subcompartment 24, because a portion of the ram member occupies the subcompartment 24. That is, the volume of subcompartment 22 will decrease at a faster rate than the volume of subcompartment 24 increases. This will result in substantial pressurization of the liquid exiting subcompartment 22, with the difference in the amount of liquid being forced to pass out of the reverse osmosis filter 74 as permeate due to closure of check valve 70 in line 52. 
     During this stage of the operation, the pressure of the liquid in subcompartment 36 will be essentially zero since the liquid contents thereof (brine in the case of salt water) will pass through a discharge line 84 through retrack valve 80. In the arrangement illustrated a relief/control valve 81 is disposed between the brine out line leading from retrack valve 80 and line 52. Such valve has been found to be of value not only for system pressure control but also as a bypass used when flushing the system after use. 
     In summary, the liquid in subcompartment 38 will be at the outlet or pressure of pump 54, e.g. 80 psi. The pressure in subcompartment 36 will be essentially zero, and the pressure of liquid in subcompartments 22, 24 will be considerably higher, e.g. 800 psi. The amount of increase will generally correspond to the ratio of the cross-sectional area of the ram to the cross-sectional area of the cylinder. 
     FIG. 2 illustrates the situation which exists sometime after second piston head 30 has contacted pilot valve 82 and displaced same to the left along with consequent displacement to the left of retrack valve 80. Now the pump 54 directs pressurized liquid to subcompartment 22 with piston heads 20 and 30 and ram member 40 moving to the right to pressurize liquid in subcompartments 36, 38 with consequent discharge of highly pressurized liquid from subcompartment 38 through filter 74, retrack valve 80 and into subcompartment 36, the excess highly pressurized liquid exiting the filter 74 as a permeate portion in the form of fresh water. Of course, this entire cycle will keep repeating itself as long as pump 54 delivers drive pressure fluid to the rest of the system.