Reverse osmosis system and automatic cycling booster pump therefor
BACKGROUND OF THE INVENTION 
     Reverse osmosis systems are commonly used for removing impurities from water, such as drinking water. A conventional reverse osmosis system includes a reverse osmosis filter having a reverse osmosis membrane. Feed water is supplied to the filter, and the filter delivers filtered product water having a reduced impurity content. Not all of the feed water supplied to the filter passes through the reverse osmosis membrane, and this unfiltered water, or brine, can be discharged to drain or a portion of it can be recycled through the filter. 
     To increase the throughput, i.e., the volume of product water, it is known to employ a pump to increase the pressure of the feed water supplied to the reverse osmosis filter. A conventional electric motor driven pump is used for this purpose. Motor driven pumps increase installation costs by requiring electrical wiring to the pump. In addition, they are subject to higher operational costs due to the cost of electricity and the cost of maintaining and repairing or replacing the electrical motor. 
     SUMMARY OF THE INVENTION 
     This invention overcomes these disadvantages while retaining the desirable results achieved by boosting the feed water pressure supplied to a reverse osmosis filter. With this invention, a pump driven by the feed water itself is used to increase the pressure of the feed water so that the reverse osmosis filter receives the feed water at increased pressure. No electrical wiring needs to be run to the pump. 
     The pump is coupled into a feed water inlet conduit between the source of feed water and the inlet port of the filter. The pump can increase the pressure of the feed water supplied to it by a desired ratio, for example, 3:1. 
     The pump can advantageously include a housing and a piston reciprocable in the housing to increase the pressure of the feed water. The pump of this invention also controls the flow of brine from the reverse osmosis filter to drain. In addition, the brine is used for certain pump control functions. The control of the flow of brine is accomplished by a brine valve. Means is provided for changing the position of the brine valve to control the flow of brine. With this invention, the change of position of the brine valve, e.g., from open to closed or closed to open, is used to reverse the direction of movement of the piston. 
     The position of the brine valve is preferably changed by a resilient coupling between the brine valve and the piston. The resilience, which can be provided by a spring, provides for closing of the brine valve after termination of the return stroke and before initiation of the next pumping stroke. Conversely, the resilient coupling provides for moving the brine valve from a partially open to a full open position after termination of the pumping stroke and before initiation of the return stroke. This resilient coupling and the sequencing of piston and brine valve movement accomplished thereby are instrumental in preventing the piston from &#34;hanging up&#34; at the end of a stroke. In other words, the brine valve, which acts as a reversing valve, allows the piston to complete each of its strokes before the brine valve is fully closed or fully opened. In addition, the resilience of the resilient coupling is energized by the piston in that it is piston movement which compresses or cocks a spring to store energy which is ultimately released to drive the brine valve closed or fully opened. 
     The housing has a cavity, and the piston reciprocates in the cavity and divides the cavity into an inlet chamber communicating with an inlet port and an outlet chamber communicating with an outlet port. To achieve a pressure boost, the piston is a differential area piston and has a first relatively large area face in the inlet chamber and a second smaller area face in the outlet chamber. This enables the fluid in the inlet chamber to drive the piston on a pumping stroke and deliver fluid at increased pressure at the outlet port. 
     In a preferred construction, the motion of the piston on the pumping stroke is terminated, and the piston is reversed by moving the brine valve to the open position. This enables brine to flow from the filter through the brine valve and a drain port on the housing to a reversing chamber in the housing which communicates with the drain port and the piston. This raises the pressure in the reversing chamber to assist reversing movement of the piston. In addition, a spring can be used to urge the piston on its return stroke. 
     In order to recharge the outlet chamber with fluid, which can be elevated to a higher pressure on the next pumping stroke, the pump includes a check valve carried by the piston. The check valve opens on the return stroke to allow fluid from the inlet chamber to flow through the check valve to the outlet chamber. The check valve opens because the opening of the brine valve provides communication between the filter and drain to thereby reduce the pressure in the outlet chamber. The check valve also constitutes a portion of the reversing means because it opens to increase the pressure in the outlet chamber over the pressure that would exist if this valve remained closed. 
     During the return stroke, feed water at boosted pressure is no longer being supplied to the filter. With this invention, the length of time required to accomplish the return stroke is minimized. 
     The brine valve is normally maintained in a closed position by differential fluid pressure. This can be accomplished, for example, by providing surfaces on the brine valve exposed to brine and fluid at drain pressure, respectively, with the brine being at the higher pressure to maintain the brine valve closed. In addition, the surface of the brine valve exposed to brine cooperates with the housing to define a valve chamber, and a bleed passage leads to the chamber. When the valve chamber is filled with fluid, e.g., brine, it cooperates with the bleed passage to serve as a dashpot to retard movement of the valve to the open position. This is particularly compatible with the resilient coupling which tends to move the valve to the fully opened position relatively slowly. 
     The invention, together with additional features and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying illustrative drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a schematic view partially in section illustrating a reverse osmosis system and a preferred embodiment of pump, which is driven by feed water under pressure. The piston is shown at the beginning of the pumping stroke. 
     FIG. 2 is a fragmentary sectional view showing a portion of FIG. 1, with the piston at the end of its pumping stroke. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The drawing shows a reverse osmosis system 11 which comprises a reverse osmosis filter 13 and a pump 15. The reverse osmosis system 11 is conventional and includes a reverse osmosis membrane 17 within a housing 19. The housing 19 has an inlet port 21, a product water outlet port 23 and a brine outlet port 25. 
     The pump 15 includes a housing 27 having a feed water inlet port 29, a feed water outlet port 31, brine inlet port 33, a brine outlet port 35 and a drain or reversing port 37. The inlet port 29 is coupled to a source 39 of feed water under pressure by a conduit 41, and the outlet port 31 is coupled by a conduit 43 to the inlet port 21 of the filter 13. Together, the conduits 41 and 43 constitute an inlet conduit which extends between the source 39 of feed water and the inlet port 21 of the filter. 
     A conduit 44 joins the brine outlet port 25 with the brine inlet port 33. A conduit 45 joins the brine outlet port 35 with the drain port 37. A drain conduit 47 extends from the conduit 45 to drain. A restricted orifice 49 is provided in the drain conduit 47. 
     Although various constructions are possible, in the preferred embodiment, the housing 27 includes a main body 51, an end section 53 containing the port 31 and attached to the main body by a retaining ring 55 and an end section 57 containing the ports 33 and 35 and suitably attached to the other end of the main body 51 in any suitable manner. The end section 53 has a sleeve portion 59. The interior of the housing 27 is hollow, and a partition 61 is retained between the main body 51 and the end section 57 and divides the interior of the housing into cavities 63 and 65 on opposite sides of the partition. 
     A piston 67 is reciprocable in the cavity 63, and divides the cavity into an inlet chamber 69 communicating with the inlet port 29, an outlet chamber 71 communicating with the outlet port 31, and a reversing chamber 73 communicating with the drain port 37. The piston 67 is a differential area piston and has a relatively large area face 75 in the inlet chamber 69 and a smaller area face 77 in the outlet chamber 71. The piston 67 also has a reversing face 78 in the reversing chamber 73. The faces 75 and 78 are on an enlarged head 79 that sealingly slides along the peripheral wall of the inlet chamber 69 and the reversing chamber 73. The face 77 is provided, in this embodiment, as an end face of a tubular stem 81 which is sealingly slidable within the sleeve portion 59 of the end section 53. The main body 51, the sleeve portion 59 and the stem 81 are preferably coaxial. The stem 81 has an annular internal shoulder 83 adjacent the face 77. A shoulder 85 is adjacent the face 75 and, in this embodiment, is provided by an end surface of a snap ring carried by the piston 67. A coil compression spring 87 acts between the end section 53 and the head 79 of the piston 67 to urge the piston downwardly as viewed in the drawing. 
     A check valve 89 is carried by the piston 67 at the face 77. The stem 81 has a passage 91 extending through it, and the check valve 89 closes and opens the upper (as viewed in the drawing) end of the passage 91. The check valve 89 may be of any kind which will open when the pressure in the passage 91 is greater than the pressure in the outlet chamber 71. In the embodiment illustrated, the check valve 89 comprises an open cage 93 suitably attached to the stem 81 at the face 77 and a resilient valve element 95 loosely axially retained within the cage and on the face 77. Accordingly, when the fluid pressure in the passage 91 exceeds the fluid pressure in the outlet chamber 71, the fluid pressure in the passage 91 forces the valve element 95 upwardly as viewed in the drawing to allow fluid flow from the passage 91 to the outlet chamber 71. Conversely, when the pressure differential across the valve element is reversed, the valve element 95 is seated tightly against the face 77 to preclude flow between the outlet chamber 71 and the passage 91. 
     A brine valve 97 controls the flow of brine from the brine inlet port 33 to the brine outlet port 35. Although the brine valve 97 may be remote from the piston 67, in this embodiment, they are closely adjacent and within the same housing. The brine valve 97 also performs a control function for the pump 15 and, therefore, may be considered as part of the pump and within the pump housing even if it is located remotely from the piston 67. 
     The brine valve 97 includes a valve element 99 and a valve seat 101 of a soft, compliant material on the end section 57 of the housing 27. The valve element 99 is movable between a closed position shown in the drawing in which the valve element 99 seats on the valve seat 101 and an open position in which the valve element 99 is moved upwardly as shown in the drawing and is axially spaced from the valve seat 101 to thereby allow the flow of brine from the brine inlet port 33 to the brine outlet port 35. The valve element 99 cooperates with the housing to define a valve chamber 102 above (as viewed in FIG. 1) the valve element. A bleed passage 103 between the valve element 99 and the partition 61 allows for the flow of brine from the brine inlet port 33 into the chamber 102. Thus, the valve element 99 has a face in the chamber 102 which is exposed to brine at brine pressure and an opposite face which is exposed to fluid at drain pressure existing in the conduit 45. 
     The brine valve 97 is opened and closed by movement of the piston 67, and for this purpose, the brine valve and the piston are resiliently drivingly coupled together. Although this can be accomplished in different ways, in this embodiment, the connection is provided by a rod 105 coupled to the valve element 99 and extending in sealed relationship through a bore of the partition 61 into the passage 91. The coupling means also includes collars 107 and 109 slidable on the rod 105 between retaining rings 111 and 113, which are fixed on the rod 105, and a coil compression spring 115 between the collars and resiliently urging the collars away from each other. The coupling means also includes the shoulders 83 and 85. 
     In use, feed water is supplied from the source 39 through the conduit 41 and the feed water inlet port 29 to the inlet chamber 69. As shown in the drawing, the piston 67 is at the lowermost position, and water at drain pressure acts in the reversing chamber 73 against the face 78 of the piston in conjunction with the spring 87 to tend to hold the piston in this lowermost position Assuming that the outlet chamber 71 is charged with feed water, the feed water at inlet pressure acting over the relatively large face 75 is sufficient to move the piston 67 on a pumping stroke (upwardly as viewed in the drawing.) to pressurize the water in the outlet chamber 71 and to force the pressurized feed water through the conduit 43 to the inlet port 21 of the filter 13. In so doing, the pump 15 boosts the pressure of the water at the source 39 to a higher pressure and delivers it to the filter 13. During the pumping stroke of the piston 67, the brine valve 97 remains closed due to the differential fluid pressure acting across the valve element 99 and the pressure on the upper end of the rod, and initially the spring 115 is compressed between the collars 107 and 109 to further urge the valve 97 toward the closed position. However, the spring 115 expands to move the collar 107 into engagement with the ring 111 as the pumping stroke progresses. 
     The reverse osmosis membrane 17 removes impurities from the water supplied to the filter 13 and delivers it to the outlet port 23 as filtered product water. Because the brine valve 97 is closed, no brine can flow from the filter 13 to drain, and consequently, the piston 67 moves on the pumping stroke to provide make up feed water at the same rate that product water is discharged at the outlet port 23. 
     As the piston 67 nears the end of the pumping stroke, i.e., approaches the position of FIG. 2, the shoulder 85 engages the collar 109 to compress the spring 115. This exerts an upward force on the valve element 99 and when this upward force is sufficient to overcome the valve closing force resulting from the differential pressure acting across the valve element 99, the valve element 99 is lifted off the seat 101 and is driven by the spring 115 to the fully open position after termination of the pumping stroke. 
     In any event, with the brine valve 97 open, brine can now flow through the conduit 44, the brine inlet port 33, the brine outlet port 35 and the conduit 45 to both the reversing chamber 73 and the orifice 49. Although the conduit 45 is open to drain via the conduit 47, the presence of the restricted orifice 49 in the conduit 47 prevents the pressure in the conduit 45 and the pressure within the reversing chamber 73 from dropping all the way to drain pressure, which may be essentially zero psig. Consequently, there is a significant pressure increase in the reversing chamber 73, and this pressure acts across the relatively large area face 78. In addition, the opening of the brine valve 97 reduces the pressure in the filter 13, the conduit 43 and the outlet chamber 71 to less than the pressure of the feed water in the inlet chamber 69. Consequently, the differential pressure acting across the check valve 89 lifts the valve element 95 to allow water to flow from the inlet chamber 69 to the outlet chamber 71. 
     The effect of this is twofold. First, the opening of the check valve 89 places the face 77 essentially at the pressure of the feed water from the source 39, and this is a pressure increase relative to the pressure which existed in the outlet chamber 71 immediately prior to opening of the check valve 89. Accordingly, the increased pressure in the outlet chamber 71 and the reversing chamber 73 in conjunction with the force of the spring 87 are sufficient to move the piston 67 downwardly on its return stroke against the force of the feed water acting against the face 75. 
     Secondly, the opening of the check valve 89 enables the outlet chamber 71 to be recharged with feed water on the return stroke. Consequently, on the next pumping stroke, the outlet chamber 71 is charged with water which can be delivered at boosted pressure to the filter 13. 
     As the piston 67 nears the end of the return stroke, the shoulder 83 contacts the collar 107 and compresses the spring 115 to thereby provide a resilient closing force on the valve element 99. When the spring is compressed sufficiently, it generates an adequate closing force to move the valve element 99 downwardly into sealing engagement with the seat 101 to thereby close the brine valve 97. However, the spring 115 closes the valve 97 after termination of the pumping stroke. This restores the conditions which existed at the beginning of the first pumping stroke described above so that the operation can be repeated. 
     From the foregoing, it is apparent that movement of the piston 67 is used to open and close the brine valve 97. Also, opening of the brine valve 97 brings about termination of the pumping stroke, and closing of the brine valve 97 brings about termination of the return stroke. Reversal of movement of the piston 67 at the end of the pumping stroke is brought about by increasing the pressure within the cavity 63 and chamber 71. 
     The valve chamber 102 and the bleed passage 103 act like a dashpot to retard movement of the valve element 99 toward either the open or closed position. This relatively slower movement of the valve element 99 in conjunction with the spring 115 assures that the piston 67 will complete its stroke before movement of the valve element 99 is completed. 
     During the return stroke, feed water at boosted pressure is no longer being supplied to the filter 13. Consequently, the length of time to accomplish the return stroke and to reseat or close the brine valve 97 should be minimized. With this invention, the forces acting on the piston 67 as described above enable the return stroke to be accomplished in a minimum length of time, such as, for example, 1.5 to 2 seconds. By way of example, the pumping stroke may last 1.5 minutes, and in this event, the portion of the cycle time devoted to the return stroke and to closing of the brine valve 97 is minimal. 
     Although an exemplary embodiment of the invention has been shown and described, many changes, modifications and substitutions may be made by one having ordinary skill in the art without necessarily departing from the spirit and scope of this invention.