Pumps for filtration systems
Improvements in product water throughput from a reverse osmosis (RO) membrane filter achieved by thinner feed spacers in the RO element, enhanced recovery (ratio of permeate to feed), pressure recovery of the retentate fluid pressure opposing the feed water pressure, and fluid pulsing of the RO element feed stream. The system of the invention preferably comprises a dual head reciprocating pump, an RO element, and a differential pressure activated (“DPA”) valve. The DPA valve, in combination with connecting the two pump heads to reduce required pump pressures, generates energy recovery. The frequency and amplitude of the reciprocating pump create a pulse wave in the RO element that improves permeate quality and throughput. A control system preferably monitors system parameters to optimize the reciprocating pump speed and amplitude in order to obtain maximum throughput and permeate quality from any given RO element configuration. Also a highly compact, portable RO system comprising a piston and a DPA valve. The piston separates the feed chamber from the retentate chamber. The pressure difference between the two chambers determines the pressure recovery of the system. The DPA valve opens and closes hydraulically to automatically control the retentate discharge as the system is pumped.
1. A membrane filtration system comprising:
a first piston, said first piston separating a feed chamber from a retentate chamber;
a membrane filtration element; and
a differential pressure activated (DPA) valve which controls retentate discharge, said DPA valve disposed downstream of said membrane filtration element and said retentate chamber with respect to a flow of retentate, said DPA valve comprising:
a single housing comprising a port in fluid connection with an inlet to said filtration element, an inlet port for receiving retentate from said filtration element, and a retentate discharge port; and
a single second piston slideably disposed within said single housing, said second piston positively sealing said inlet port when a feed pressure on a first face of said second piston exceeds a retentate pressure on a second face of said second piston;
wherein pressure recovery is provided by a pressure difference between the feed chamber and the retentate chamber acting on said first piston.
2. The membrane filtration system of claim 1 wherein the DPA valve is hydraulically operated.
3. The membrane filtration system of claim 1 wherein operation of the DPA valve is determined by relative pressure in the feed chamber and the retentate chamber.
4. The membrane filtration system of claim 3 wherein the DPA valve operates automatically in accordance with pumping of said first piston.
5. The membrane filtration system of claim 1 wherein said first piston comprises a piston shaft.
6. The membrane filtration system of claim 5 wherein a recovery ratio of the membrane filtration element is determined by a cross-sectional area of the piston shaft.
7. The membrane filtration system of claim 6 wherein the piston shaft is easily replaceable, thereby enabling rapid change of the recovery ratio.
8. The membrane filtration system of claim 1 further comprising a pressure relief valve.
9. The membrane filtration system of claim 1 comprising a single cylinder.
10. The membrane filtration system of claim 1 having a diameter of less than approximately four inches.
11. The membrane filtration system of claim 10 having a diameter of less than approximately two inches.
12. The membrane filtration system of claim 1 having a length of less than approximately twenty-four inches.
13. The membrane filtration system of claim 12 having a length of less than approximately fifteen inches.
14. The membrane filtration system of claim 1 having a weight of less than five pounds.
15. The membrane filtration system of claim 14 having a weight of less than three pounds.
16. The membrane filtration system of claim 1 wherein said membrane filtration element comprises a reverse osmosis element.
17. The membrane filtration system of claim 16 wherein said reverse osmosis element comprises a spiral wrapped element.
18. The membrane filtration system of claim 17 wherein said spiral wrapped element comprises:
at least one membrane; and
at least one thin feed spacer.
19. The membrane filtration element of claim 18 wherein said at least one thin feed spacer comprises a plastic web mesh.
20. The membrane filtration system of claim 18 wherein said at least one thin feed spacer is less than approximately 0.025 inches thick.
21. The membrane filtration system of claim 20 wherein said at least one thin feed spacer is less than approximately 0.011 inches thick.
22. The filtration system of claim 18 wherein said at least one thin feed spacer provides for a reduction in an amount of total dissolved solids at a surface of said membrane.
23. The filtration system of claim 1 wherein the pressure recovery is great enough to enable manual operation of the system.
24. The filtration system of claim 23 wherein the pressure recovery is about fifty percent.
25. A method of filtering a substance comprising the steps of:
pumping the substance with a first piston, wherein the first piston separates a feed chamber and a retentate chamber;
passing the substance through at least one membrane filtration element, thereby separating the substance into permeate and retentate; and
discharging the retentate using a differential pressure activated (DPA) valve, the DPA valve disposed downstream of the membrane filtration element and the retentate chamber with respect to a flow of the retentate, the DPA valve comprising:
a single housing comprising a port in fluid connection with an inlet to said filtration element, an inlet port for receiving retentate from said filtration element, and a retentate discharge port; and
a single second piston slideably disposed within said single housing, said second piston positively sealing said inlet port when a feed pressure on a first face of said second piston exceeds a retentate pressure on a second face of said second piston.
26. The method of claim 25 wherein the passing step comprises passing the substance through a reverse osmosis filtration element.
27. The method of claim 25 wherein the discharging step comprises operating the DPA valve hydraulically.
28. The method of claim 25 wherein the discharging step comprising operating the DPA valve according to the relative pressure in the feed chamber and the retentate chamber.
29. The method of claim 28 wherein the discharging step comprising operating the DPA valve automatically as the substance is pumped.
30. The method of claim 25 wherein the pumping step comprises utilizing a pressure difference between the feed chamber and the retentate chamber acting on said first piston to reduce the force necessary to pump the substance.