A WATER-PURIFICATION UNIT WITH CONSTANT-FLOW VALVE

Abstract: A water-purification unit comprising a module (9) for reverse osmosis with an inlet (8) for non-purified water, an outlet (14) for purified water and an outlet (20a) for non-purified water. In order to ensure in a simple manner that a minimum amount of water flows through the module at all times, the outlet (20a) for non-purified water is connected to a drain (24) via a constant-flow valve (22-23). The same outlet may also be connected to a flushing valve (28) connected parallel with the constant-flow valve (22-23) and to a pressure control valve (27) via which non-purified water can be recycled.

Description: TITlE A WATER-PURIFICATION UNIT WITH CONSTA?(T-FIOW VALVE SECHNICAT FIELD The present invention relates to a water-purification unit comprising a module for reverse osmosis with an inlet for non-purified water, an outlet for purified water and an outlet for non-purified water. Such a module comprises diaphragms of optional shape but of a composition designed to let through substantially only water molecules and molecules of the same order of magnitude. The diaphragms consist preferably of hollow fibres, but they may also take the form of plane films. If such a module contains pure water on the one side of a diaphragm and impure water on the opposite side, the socalled osmotic effect causes pure water to endeavour to force its way across to the impure side to produce dilution and to even out the concentration. The concept of reverse osmosis here means that the pressure on the impure side is increased, so that the osmosis effect is offset and the water instead passes over from the impure side to the pure side. BACKGROUND ART A water-purification unit of the abovementioned type has the disadvantage that it silts up easily, unless sufficiently large amounts of water constantly flush through the same. It has been attempted earlier to achieve this by constantly allowing a portion of the non-purified water to be conducted from the module to a drain and another portion to be recycled from the outlet for the non-purified water to the inlet for the same. These two flows were separately controlled which in practice proved to be very difficult as well as making all servicing and repair work more complicated. DISCLOSURE OF INVENTION The abovementioned problem is solved in accordance with the invention in that the outlet for non-purified water is connected to a drain via a constant-flow valve which produces at least the minimum flow required to pass through the module. In a preferred embodiment a special flushing valve is connected parallel with the constant-flow valve. This flushing valve is adapted so that on flushing of the module it lets through a substantially greater flow than the constant-flow valve. The module can be effectively flushed':: therefore if, in spite of the invention, it should still silt up. This flushing valve is used moreover to achieve an effective flushing through the module after chemical sterilization of the same. In principle a normal#water-main pressure may be used as the input pressure in the unit according to the invention, but it is preferable to arrange a pressure pump connected between the water intake and the module which, like the rest of the unit, is adapted so that it can start only after a pressure pick-off arranged between it and the water intake has established that sufficient pressure exists in the water intake. In this way it is ensured that the module obtains a sufficient amount of water. To ensure the function of the unit it is possible moreover to provide a return pipe starting from the outlet for purified water and which can be connected via a nonreturn valve either to a drain or to a point of the system upstream of the inlet for non-purified water. In this way purified water, if it cannot be used for other purposes, can be returned to the inlet side of the module. It is possible that the efficiency of the module deteriorates in time. To make sure that this is detected, it is appropriate to arrange a first conductivity meter upstream of the inlet for non-purified water and a second conductivity meter downstream of the outlet for purified water. By a comparison of the values read off these meters the purifying efficiency of the module can be evaluated. At the same time a reliable check on the outgoing purified water can be obtained by means of the second conductivity meter. For a check of the pressure in the module and for an economic utilization of the water input, the flow from the outlet for non-purified water can be adapted so that it is divided:':between the said constant-flow valve and an adjustable valve for the control of the pressure in the module. From this adjustable valve the excess water in this case is returned to a point in the system upstream of the inlet for non-purified water. The efficiency of the unit can be improved by providing means for the heating of the incoming water. This may be done in such a manner that the driving motor of the pressure pump is adapted so that it cools the water input. In this way the efficiency of the module is increased by the heating of the incoming water obtained in this manner. The invention can be used in many fields where the need for abs olutely pure water exists, e.g. in connection with haemodialysis, peritoneal dialysis or haemofiltration. In all these processes water is used for the purification of blood and a more or less high degree of sterility is required. The arrangement in accordance with the invention is appropriately provided therefore with an intake for sterilizing agent arranged near the water inlet. This intake should be provided appropriately with means adapted to ensure that only sterilization programmes can be performed when this intake is connected to a source of sterilizing agent. In this manner a patient cannot be exposed to any risk of coming into contact with the sterilizing agent. BRIEF DESCRIPTION OF DRAWINGS In the following the invention will be described in greater detail with reference to the enclosed drawings which show, by way of example, à preferred embodiment of the same. Figure 1 shows a block diagram for the unit as a whole Figure 2 shows a constant-flow valve included in the unit. BEST i#T)E OF TARRYING OUT THE INVENTION In the block diagram of a preferred embodiment of the subject of the invention shown in fig.1 a water inlet is designated 1. From the water inlet the water flows through an inlet valve 2 shown schematically, which for example may be a conventional solenoid valve. At a point 3 the pressure of the water is measured by means of a pressure gauge 4. From the point 3 the water is conducted further via a branch point 5 a conductivity meter 6 and a pump 7 to the inlet 8 of a module 9 for reverse osmosis. In the course of this the water ie preferably heated by being used at the same time for the cooling of the pump motor 10. The module 9 is divided into a pure water side 11 and an input side 12. These sides are separated by a diaphragm 13 indicated schematically. The purified water is conducted out via an outlet 14 and monitored with the help of a conductivity meter 15. The purified water is passed via a valve 16 to a place of consumption, e.g. an apparatus for haemodialysis. From a branch point 17 the excess water is conducted via a return pipe 18, which contains a non-retllrn valve 19. Through this return pipe 18 the excess water can be returned to the point 5 upstream of the inlet 8 to the module 9. This is done when the unit is used, for example, in haemodialysis. For haemofiltration or peritoneal dialysis, which require a higher degree of sterility, the pipe 18 can be connected instead directly to a drain. This will exclude any risk of impure water being able to pass the module 9 under any circumstances, e.g. through a fault in the non-return valve 19. From the side 12 of the module 9 non-purified water is conducted via an outlet 20a and the pipe 20 to a dis tributing point 21. By means of a constant-flow valve 22-23 connected to this point it is ensured that a small amount of liquid is conducted at all times from the module 9 through the pipe 20 and further to a drain 24. Numerals 22-23 thus designate a constant-flow valve, which may be of the design as shown in fig.2. Lines 22a and 22b together with the spring 23a indicate that the valve is acted upon from one direction by the input pressure, whilst from the opposite direction it is acted upon partly by the secondary pressure and partly by a spring pressure. The liquid may also pass through a throttle 25. The part of the liquid in the pipe 20 which does not go through the constant-flow valve is conducted instead through a pipe 26 and an adjustable valve 27, e.g. a needle valve, back to point 3 and further through point 5 to the inlet 8 of the module 9. The module may nevertheless become silted up or obstructed in some other manner and therefore requires flushing through from time to time. For this purpose a special flushing valve 28 is arranged parallel with the constant-flow valve 22-23. when the valve 28 is opened, larger amounts of liquid can be flushed through the input side 12 of the module 9. To make it possible to sterilize the system, it is provided with an intake 29 for sterilizing agent. This intake is provided with an optical system 30, shown schematically, which is capable of detecting whether or not the intake is connected to a source of sterilizing agent. If such a source is connected, only special sterilization programmes can be carried out, which means that there is no risk then of any patient coming into contact with the sterilizing agent. This sterilizing agent is thus conducted from the intake 29 via a nonreturn valve 31 and a shutoff valve 32 to the point 5 which should be located as near as possible to the inlet valve 2. The constant-flow valve 22-23 may be of any type. However, in practice the valve 23a shown in fig.2 has proved to be suitable. This valve 23a is provided with an inlet side 33 and an outlet side 34. In between are a pressure chamber 35 and a spring 36. The pressure chamber is separated from the inlet side 33 by a piston 37 which has a throughhole 38 and is encircled by a sealing ring 39. The piston 37 is arranged so that it partially covers a duct 40 between the pressure chamber 35 and the outlet 34. Then the pressure on the input side 33 is increased, the duct 40 is throttled, so that the pressure is automatically increased also in the pressure chamber 35. This in turn gives rise to a substantially constant flow through the ducts 38 and 40. Theoretically the constant-flow valve can be explained in the following manner. Force on the primary side of the piston: F1 = P1 x Apiston Force on the secondary side of the piston: F2 = (P1 - AP) X ApistOn Fspring; When the system is in equilibrium F1 = F2, that is to say P x A = (P1Apiston -AP) x Apiston spring or simplified: AP Piston t spring Since the piston area is constant,p will be directly proportional to the Fspring. The spring force varies very little within the working range and we obtain therefore a A P which is practically constant. Owing to > p being essentially constant, and in combination with a fixed throttling, 2 constant flow is therefore obtained. Whilst the valve described above has proved to be suitable, it will nevertheless be clear. to those versed in the art that other types of conventional constant-flow valves may also be used. With regard to the cooling of the motor-driven pump, reference is made to the Dàtent application submitted at the same time, entitled "A water-purification unit with lisuid-cooled pump motor". Naturally, the invention is not limited exclusively to the embodiment described above, but can be varied within the scope of the following claims.

Claims: CIAISTS 1. A water-purification unit comprising a module (9) for reverse osmosis with an inlet (8) for non-purified water, an outlet (14) for purified water and an outlet (20a) for non-purified water, c h a r a c t e r i z e d i n t h a t the outlet (20a) for non-purified water is connected to a drain (24) ,via a constant-flow valve (22-23). 2. A unit in accordance with claim 1,. c h a r a c t e r i z e d by a flushing valve (28) connected parallel with the constant-flow valve (22-23) which is adapted so that on flushing of the module (9) it lets through a substantially greater flow than the constant-flow valve (22-23). 3. A unit in accordance with claim 1 or 2, c h a r a c t e r i z e d by a pressure pump (7) connected between the water intake (1) and the module (9) which like the rest of the unit is adapted so that it can start only after a pressure pick-off (4) arranged between it and the water intake has established that sufficient pressure exists in the water intake. 4. An arrangement in accordance with any one of the preceding claims, c h a r a c t e r i z e d b y a return pipe (18) arranged so as to start from the outlet (14) for purified water and which can be connected via a non-return valve (19) either to a drain (e.g. 24) or to a point (5) of the system upstream of the inlet (8) for non-purified water. 5. An arrangement in accordance with any one of the preceding claims, c h a r a c t e r i z e d b y a first conductivity meter (6) arranged upstream of the inlet (8) for non-turified water and a second conductivity meter (15) arranged downstream of the outlet (14) for purified water, whose values can be compared in order to evaluate the purification efficiency of the module (9). 6. An arrangement in accordance with any one of the preceding claims, eh a r a c t e r i z e d i n t h a t the flow from the outlet (20a) for non-purified 1water is adapted, so that it is divided between the said constant-flow valve (22-23) and an adjustable valve (2i) for the control of the pressure in the module (9). 7. An arrangement in accordance with any one of the preceding claims, c h a r a c t e r i z e d b y means (10) for the heating of the incoming water. 8. An arrangement in accordance with claims 3 and 7, c h a r a c t e r i z e d i n t h a t the driving motor (10) of the pressure pump (7) is adapted so that it is cooled by the incoming water, as a result of which the efficiency:*of the module (9) is increased through the heating obtained in this manner. 9. An arrangement in accordance with any one of the preceding claims, c h a r a c t e r i z e d b y an intake (29) for sterilizing agent arranged near the water inlet (1) and provided with means (30) adapted to ensure that only sterilization programmes can be performed when this intake (29) is connected to a source of sterilizing agent.

Inventors: JONSSON, ULF LENNART PERCY, Jönsson, Ulf Lennart Percy
Applicants: GAMBRO LUNDIA AB
Application year: 1982
Main classification: C02F1
IPC codes: B01D61, C02F1, A61M1, B01D65