Title of Invention

"FLUID OPERATED PUMPS AND APPARATUS EMPLOYING SUCH PUMPS"

Abstract

A fluid-operated pump comprising recriprocable means (1) having a pair of first (30, 31) pressure surfaces and a pair of second (32, 33} pressure surfaces each bounding a respective first (21, 22) and second (19, 20) pressure chamber, control valve means (3, 4, 5, 6) to supply pressure fluid alternately to one said first chamber and to exhaust pressure fluid from the other said first chamber thereby causing the reciprocale means to reciprocate, fluid inlet and outlet valve means (7, 8, 9, 10) communicating with the second chambers (19, 20) whereby the second pressure surfaces are arranged to pump fluid through the second chambers upon reciprocation of the reciprocable means, characterized in that the control valve means comprises a plurality of poppet valves (3, 4, 5, 6) the poppet valves being exposed to the pressure of fluid in the first chambers and each having a bleed valve (23, 24, 25, 26) to permit limited flow past the poppet valve and reduce a force required to operate the poppet valve.

Full Text

-2- The invention relates to a fluid-operated pump suitable for use in a reverse osmosis or filtration system for example a water purifying system, and to an apparatus employing such a pump. The preferred embodiment of the current invention provides a high pressure fluid output flow from two or more lower pressure fluid input flows. It is specifically but not exclusively intended to provide high pressure water for purification by reverse osmosis, where water contaminated by unwanted solutes is forced, at a pressure typically 60 bar, through a semi-permeable membrane, effectively filtering out those solutes. This process is typically used for desalination of seawater. It is a characteristic of reverse osmosis that the flow of contaminated water across the membrane needs to be typically ten times greater than the flow of purified water through the membrane, the excess flow acting to flush away contaminants accumulated at the membrane surface. In the simplest systems, this high pressure flushing flow is released to waste, taking with it, and wasting, typically 90% of the energy used to provide the high pressure input flow. There are established methods to recover the energy contained in the high pressure flushing flow ... It may be used to drive a hydraulic motor mechanically coupled to the pressurizing pump, with the balance of energy input provided by, for example, an electric motor. This method is complex and consequently expensive, with inevitable inefficiencies in the indirect mechanical transfer of energy. Standard, relatively inexpensive, hydraulic motors cannot be used since they are designed for use with hydraulic oils, relying on them for lubrication. -3- It may be used more directly to provide part of the energy used by the pressurizing pump. US patents Re.32,144 and Re.33,135 describe mechanically driven reciprocating- piston pumps where one side of the piston and cylinder act as a a pump and the other side acts as a motor, driven by the flushing flow to provide most of the pumping power. A further characteristic of reverse osmosis is that the contaminated water input flow needs to be thoroughly filtered, to prevent clogging of the membrane by particulates. It is often cost-effective to provide an additional low-pressure pump to drive the contaminated water input flow through the filter, since this allows a higher pressure drop across the filter, typically 1 bar, enabling a smaller and cheaper filter to be used. Without this additional pump, the pressure drop across the filter would be limited to around 0.5 bar by the poor ability of the high pressure pump to suck against low pressures. The additional pump will also be required if, as is often the case, the high pressure pump is not self-priming. The preferred embodiment of the invention is directed to avoiding or mitigating at least some of the disadvantages of these known devices. In one aspect the invention provides a fluid-operated pump comprising recriprocable means having a pair of first pressure surfaces and a pair of second pressure surfaces each bounding a respective first and second pressure chamber, control valve means to supply pressure fluid alternately to one said first chamber and to exhaust pressure fluid from the other said first chamber thereby causing the reciprocable means to reciprocate, fluid inlet and outlet valve means communicating with the second chambers whereby the second pressure surfaces are arranged to pump fluid through the second chambers upon reciprocation of the reciprocable means, characterized in that -4- the control valve means comprises a plurality of poppet valves the poppet valves being exposed to the pressure of fluid in the first chambers and each having a bleed valve to permit limited flow past the poppet valve and reduce a force required to operate the poppet valve. Preferably, the poppet valve is mechanically biased by biasing means, the bleed valve is arranged to modify the pressure in the respective first chamber to reduce the required operating force to less than the mechanical bias to which the poppet valve is subjected. In an embodiment, the poppet valve may be arranged for admitting pressure fluid to a said first chamber, the valve is arranged so as to be held closed buy a pressure difference across it when the to provide a force for opening the poppet valve when the pressure in the first chamber is relatively high. In another embodiment, the poppet valve is arranged for exhausting pressure fluid from a said first chamber, the valve is arranged so as to be held closed buy a pressure difference across it when the pressure in the first chamber is relatively high, the bleed valve is able to permit the escape of pressure fluid from the first chamber, and the biasing means is arranged so as to provide a force for opening poppet valve when the pressure at the first chamber is relatively low. Preferably, the reciprocable means is a pair of connected pistons. The pistons may be coaxial and the first pressure surfaces of the piston may face in opposite directions. The first chambers bounded by the first pressure surfaces may be arranged between those surfaces and separated by common wall structure. Preferably, the control valve means is arranged so as to be operated by the pistons when the pistons reach the extremities of their stroke: The control valve means is disposed in the common wall structure. -5- The two poppet valves in the common wall structure may comprise a movable element which is common to both valves. The poppet valve preferably comprises a movable element stable only at the extremes of its travel. The second pressure surfaces are of greater effective area than the first pressure surfaces. The present invention also provides a reverse osmosis or filtration system incorporating a pump in which the second pressure surfaces are of greater effective area than the first pressure surfaces and the difference in swept volume between the second chambers and the first chambers provides pressure fluid which passes through a semi-permeable membrane or filter of the system. Preferably, a return flow from the semi-permeable membrane or filter is applied to the pump as said pressure fluid. In a preferred embodiment, a reverse osmosis or filtration system comprising a semi-permeable membrane or filter and a pump as described above is arranged to supply all high pressure fluid delivered to the membrane or filter, the membrane or filter being arranged to deliver part of said fluid as purified or filtered fluid, and to return the remainder to the pump as return fluid, the pump being powered only by the return fluid and by an inlet flow of pressurized fluid to be purified or filtered. It is a feature of the preferred forms of the invention that single moving elements each act as both pump and motor, with a driving pressure applied to one part of each element while another part pressurizes the pumped flow. In a preferred embodiment the pumps provide the high pressure input flow to the semi-permeable membrane, and are driven by the motors. One motor is powered by the high pressure flushing flow leaving the membrane, while the other is powered by the contaminated water input flow. This input flow is provided at moderate pressure, typically 5 to 10 bar by a separate pump, which may be of a conventional type. -6- The benefits provided by the preferred embodiment of the current invention are ... It recovers the energy otherwise wasted in the high pressure flushing flow, increasing system efficiency typically by a factor of 10. It has minimal mechanical losses, since the driving pressure is applied as directly as possible to provide pumping effort. It offers great simplicity, and consequent low manufacturing cost, since mechanical drives and linkages are eliminated. It enables the system to b powered by a single self-printing, externally-driven pump. Since this need deliver only moderate pressure, it may be of a common, mass-produced and consequently inexpensive type. The preferred form of the current invention differs from existing hydraulic intensifies, which provide a single high pressure output flow from a single moderate pressure input flow, in that it receives two input flows, one at high pressure and one at moderate pressure, to provide a single high pressure output. In particular, when used in a reverse osmosis apparatus, it differs from those described in US Patents Re.32,144 and Re.33,135, mentioned above, in that all of the driving power is provided by the contaminated water input flow, and none by other mechanical means. Re.32,144 covers supplementation, only, of mechanical power input by pressurization of the feed fluid, since the mechanical drive is required to maintain the sequence of operations and to drive the valve mechanism. Brief Description of the Accompanying Drawings A preferred embodiment of the invention will now be described by way of example only with reference to the accompanying drawings, in which : -7- Figures 1 to 4 are schematic cross-sections of a preferred pump at various stages of its operating cycle. Figure 5 shows a reverse osmosis system incorporating the pump of Figures 1 to 4. Detailed description of the Accompanying Drawings Figure 1 shows the device at start up. A piston assembly, 1, consists of two pistons, one at either end of a piston rod. The piston assembly can move freely inside a cylinder assembly, 2, with seals to prevent leakage between the cylinders around the piston rod, and between each end of each cylinder around each piston. Water may flow into and out of each end of each cylinder through eight valves, 3 to 10. Valves 7 to 10 are non-return valves held closed by spring means and opened by water pressure. Valves 4 and 5 are rigidly connected to each other, and are operated by spring means which protrude into the cylinders, where they are contacted by the pistons. A spindle, 11, passes through the hole in the valve assembly, 4 and 5, with clearance to allow flow through the hole. At each end of the spindle there are pilot valve means, 24 and 25, which, when one or other are closed, seal the spindle hole. Valves 3 and 6 are flexibly connected together by a spring means, and are operated by contact with the pistons. A spindle, 12, passes through holes in valves 3 and 6, with clearance to allow flow through the holes. At each end of the spindle there are pilot valve means, 23 and 26, which, when closed, seal the adjacent holes. Ports 13 and 14 are connected to a medium pressure water supply. Ports 15 and 16 are connected to the high pressure inlet of a reverse osmosis membrane. Port 17 connects with the high pressure flushing water outlet of the membrane. Port 18 exhausts water to waste at low pressure. -8- When the medium pressure water supply is applied to ports 13 and 14, water flows into the outer cylinders 19 and 20, through valves 7 and 10, then out through valves 8 and 9 to the membrane via ports 15 and 16. Flushing water returning from the high pressure side of the membrane enters the inner cylinders via port 17 and valves 4 and 5. It then exhausts to waste at low pressure via valves 3 and 6 and port 18. Valve pairs 4 and 5,and 3 and 6, are configured to be stable only at their extremes of travel when water is passing through them. This causes, for example, valves 4 and 6 to close while valves 3 and 5 are open. Pilot valves 25 and 26 are also closed by the pressure across them. Closure of these valves stops water flow, causing valves 7, 8, 9 and 10 to close under spring pressure. Figure 2 shows the next stage of operation. The outer cylinders, 19 and 20, and the right hand inner cylinder, 22, are ail at medium pressure. The left hand inner cylinder, 21, is at low pressure, being open to waste via valve 3. The overall pressure differential across the pistons cause the piston assemble to move to the tight, creating water flow which opens valves 7 and 9, while leaving valves 8 and 10 closed. Water from the right hand outer cylinder now flows out to the the membrane through port 16, and returns through port 17 into the right hand inner cylinder. The outward flow is greater than the return flow, since the cross-sectional area of the outer cylinder is greater than that of the inner cylinder, by an amount equal to the cross-sectional area of the piston rod. Because of this, the pressure on the high pressure side of the membrane increases, forcing the excess outward flow through the membrane, purifying it in the process. The piston assembly will continue to move, forcing water through the membrane, provided that... Pm.Ao > Pl.Ai + Ph.Ao - (Ph-dP).Ai where .... -9- Pm = medium pressure, applied to drive the system PI = low pressure, to which waste water exhausts Ph = high pressure, applied to membrane dP = pressure drop of membrane flushing flow Ao = cross-sectional area of outer cylinder Ai = cross-sectional area of inner cylinder (= Ao - cross-sectional area of piston rod) or, rearranging and assuming low pressure = O ... Pm > Ph.(1 -Ai/Ao) + dP.Ai/Ao ... where (1 - Ai/Ao) is the ratio of freshwater output flow to flushing water flow. This would typically be 0.1, while the membrane pressure would be 60 bar, implying a driving pressure of around 7 bar. Figure 3 shows the next stage of operation, where the piston assembly has reached the end of its stroke. The left-hand piston has contacted and closed valves 3 and 23, compressed the spring between valves 3 and 6, compressed the spring on valve 4, and opened pilot valve 25 without closing pilot valve 24, and opened pilot valve 26. The flow through pilot valve 26 is restricted to minimize the loss of high pressure water to waste. Valves 7, 8, 9 and 10 close under spring pressure since the flow through them is stopped. There is high pressure in the right-hand inner and outer cylinders, and medium pressure in the left-hand inner and outer cylinders. Valve 4 is held closed by the pressure differential across it until the left-hand inner cylinder has reached high pressure, via flow through pilot valves 24 and 25. Valve 4 is then opened by its associated spring, and valve 5 closes. Once valve 5 is closed, flow through pilot valve 26 reduces the right hand inner cylinder pressure to low pressure and valve 6 is opened by the spring connecting it to valve 3 At this point there is high pressure in the left-hand inner and right-hand outer cylinders, low pressure in the right-hand inner cylinder, and medium pressure in the left- -10- hand outer cylinder, causing the piston assembly to start moving to the left. As soon as this happens, valve 10 opens to admit medium pressure to the right-hand outer cylinder and valve 8 opens to release high pressure to the membrane. This state is shown in Figure 4, and is a mirror image of the state shown in Figure 2, while the stroke reversal at the end of the leftward-moving stroke is a mirror image of that described for Figure 3. The piston assembly thus continues to oscillate. Figure 5 shows diagrammatically a reverse osmosis system utilizing the pumps of Figures 1 to 4. A semi-permeable membrane 50 is disposed in a pressure vessel 52, so that a proportion of brine delivered to one (high pressure) side 54 of the membrane permeates through the membrane to the other (low pressure) side 56 thereof and is thereby purified as known per se. The pure water thereby obtained is taken to a storage tank 58. The brine is abstracted from the sea 60 (the system typically may be installed in a yacht or other vessel) by a conventional electrically, or mechanically driven medium pressure sea-water pump 62 and delivered to an inlet 13, 14 (Figures 1 to 4) of high pressure pump or intensifier 64, which is as already described. High pressure brine is delivered from outlets 15, 16 to the vessel 52. That proportion of the brine which does not pass through the membrane flushes through the high pressure side 54 of the vessel 52 and returns still under high pressure to inlet 17 of pump 64. The flushing flow, and the medium pressure flow to inlets 13 and 14, drive the pump 64 as its sole source of power. The flushing flow discharged from outlet 18 of the pump 64 is returned to the sea 60. It will be appreciated that the pump as described may be employed with any form of reverse osmosis or filtration system in which the flow leaving the osmosis or filtration element is still under significant pressure. -11- Each feature disclosed in this specification (which term includes the claims) and/or shown in the accompanying drawings may be incorporated in the invention independently of other disclosed and/or illustrated features. The appended abstract is repeated as part of the specification. A reverse osmosis or filtration system uses one or more hydraulic intensifiers (integrated motor and pump) to provide all the high pressure fluid to a semi-permeable membrane or filter, the intensifier being powered by the high pressure flushing flow leaving the membrane or filter, and by a pressurized inlet flow of fluid to be purified or filtered. The intensifier or pump comprises reciprocable means having a pair of first pressure surfaces and a par of second pressure surfaces each bounding a respective first and second pressure chamber, control valve means to supply pressure fluid alternately to the chamber bounded by one of the first surfaces and to exhaust pressure fluid from the chamber bounded by the other of the first surfaces thereby causing the reciprocable means to reciprocate, fluid inlet and outlet valve means communicating with the chambers bounded by the second surfaces whereby the second surfaces pump fluid through the second chambers upon reciprocation of reciprocable means, the control valve means comprising a plurality poppet valves each having a secondary bleed valve to reduce a force necessary to operate the valve. -12- WE CLAIM : 1. A fluid-operated pump comprising recriprocable means (1) having a pair of first (30, 31) pressure surfaces and a pair of second (32, 33) pressure surfaces each bounding a respective first (21, 22) and second (19, 20) pressure chamber, control valve means (3, 4, 5, 6) to supply pressure fluid alternately to one said first chamber and to exhaust pressure fluid from the other said first chamber thereby causing the reciprocable means to reciprocate, fluid inlet and outlet valve means (7, 8, 9, 10) communicating with the second chambers (19, 20) whereby the second pressure surfaces are arranged to pump fluid through the second chambers upon reciprocation of the reciprocable means, characterized in that the control valve means comprises a plurality of poppet valves (3, 4, 5, 6) the poppet valves being exposed to the pressure of fluid in the first chambers and each having a bleed valve (23, 24, 25, 26) to permit limited flow past the poppet valve and reduce a force required to operate the poppet valve. 2. A pump as claimed in claim 1, wherein a said poppet valve (3, 4, 5, 6) is mechanically biased by biasing means, the bleed valve (23, 24, 25, 26) being arranged to modify the pressure in the respective first chamber to reduce the required operating force to less than the mechanical bias to which the poppet valve is subjected. 3. A pump as claimed in claim 2, wherein a said poppet valve (4) is arranged for admitting pressure fluid to a said first chamber, the valve being arranged so as to be held closed by a pressure difference across it when the pressure in the first chamber (21) is relatively low, the bleed valve (24) being able to supply pressure fluid to said first chamber, and the biasing means (34) being arranged so as to provide a force for opening the poppet valve when the pressure in the first chamber is relatively high. 1. -13- 4. A pump as claimed in claim 2 or claim 3, wherein a said poppet valve (6) is arranged for exhausting pressure fluid from a said first chamber (22), the valve being arranged' so as to be held closed by a pressure difference across it when the pressure in the first chamber is relatively high, the bleed valve (26) being able to permit the escape of pressure fluid from the first chamber, and the biasing means (36) being arranged so as to provide a force for opening poppet valve when the pressure at the first chamber is relatively low. 5. A pump as claimed in any one or more of claims 1 to 4, wherein the reciprocable means (1) is a pair of connected pistons. 6. A pump as claimed in claim 5, wherein pistons are coaxial and the first pressure surfaces (30, 31) of the piston face in opposite directions. 7. A pump as claimed in claim 6, wherein the first chambers (21, 22) bounded by the first pressure surfaces (30, 31) are arranged between those surfaces and are separated by common wall structure (37). 8. A pump as claimed in any one or more of claims 1 to 7, where the control valve means (3, 4, 5, 6) is arranged so as to be operated by the pistons when the pistons reach the extremities of their stroke. 9. A pump as claimed in claim 7 or claim 8, wherein said control valve means (3, 4, 5, 6) is disposed in the common wall structure (37). 10. A pump as claimed in claim 9, wherein two said poppet valves (4, 5) in the common wall structure (37) comprise a movable element which is common to both valves. 4. -14- 11. A pump as claimed in any one or more of claims 1 to 10, wherein a said poppet valve (3, 4, 5, 6) comprises a movable element stable only at the extremes of its travel. 12. A pump as claimed in claimed in any one or more of claims 1 to 11, wherein the second pressure surfaces (32, 33) are of greater effective area than the first pressure surfaces (30, 31). 13. A reverse osmosis or filtration system (52, 62, 64) incorporating a pump (64) as claimed in any one or more of claims 1 to 12. 14. A system as claimed in claim 13, wherein the pump (64) is as claimed in claim 12 and the difference in swept volume between the second chambers (32, 33) and the first chambers (31, 31) provides pressure fluid which passes through a semi-permeable membrane or filter (50) of the system. 15. A system as claimed in claim 13 or claim 14, wherein a return flow from the semi-permeable membrane or filter (50) is applied to the pump (52) as said pressure fluid. 16. A reverse osmosis or filtration system comprising a semi-permeable membrane or filter (50), a pump as claimed in any of claims 1 to 12 arranged to supply all high pressure fluid delivered to the membrane or filter, the membrane or filter being arranged to deliver part of said fluid as purified or filtered fluid, and to return the remainder to the pump as return fluid, the pump (64) being powered only by the return fluid and by an inlet flow of pressurized fluid to be purified or filtered. 17: A fluid-operated pump, substantially as herein described, particularly with reference to and as illustrated in the accompanying drawings. -15- 18. A reverse osmosis or filtration system, substantially as herein described, particularly with reference to and as illustrated in the accompanying drawings. Dated this 21st day of November 1997. A fluid-operated pump comprising recriprocable means (1) having a pair of first (30, 31) pressure surfaces and a pair of second (32, 33} pressure surfaces each bounding a respective first (21, 22) and second (19, 20) pressure chamber, control valve means (3, 4, 5, 6) to supply pressure fluid alternately to one said first chamber and to exhaust pressure fluid from the other said first chamber thereby causing the reciprocale means to reciprocate, fluid inlet and outlet valve means (7, 8, 9, 10) communicating with the second chambers (19, 20) whereby the second pressure surfaces are arranged to pump fluid through the second chambers upon reciprocation of the reciprocable means, characterized in that the control valve means comprises a plurality of poppet valves (3, 4, 5, 6) the poppet valves being exposed to the pressure of fluid in the first chambers and each having a bleed valve (23, 24, 25, 26) to permit limited flow past the poppet valve and reduce a force required to operate the poppet valve.

Documents:

02201-cal-1997-abstract.pdf

02201-cal-1997-claims.pdf

02201-cal-1997-correspondence.pdf

02201-cal-1997-description (complete).pdf

02201-cal-1997-drawings.pdf

02201-cal-1997-form-1.pdf

02201-cal-1997-form-2.pdf

02201-cal-1997-form-3.pdf

02201-cal-1997-form-5.pdf

02201-cal-1997-pa.pdf

02201-cal-1997-priority document.pdf