Dialysis machine and constant flow regulator

Abstract

A dialysis machine, in particular for hemodialysis and/or hemofiltration, having a dialyzate system and having a water inlet via which the dialyzate system can be connected to an external water supply. The dialysis machine includes a constant flow regulator that is arranged between the water connection and the dialyzate system.

Claims

1. A dialysis machine, comprising, wherein the dialysis machine is configured to be used for at least one of hemodialysis and hemofiltration: a dialyzate system having a water inlet chamber; a water inlet via which the dialyzate system can be connected to an external water supply providing ultra-pure water; a constant flow regulator provided between the water inlet and the water inlet chamber of the dialyzate system; and said water inlet chamber including a level detection and an inlet valve, with a control of the dialysis machine controlling the inlet valve in dependence on the level detection, said constant flow regulator being configured as a passive flow control element and arranged to provide a substantially constant flow into the water inlet chamber when the inlet valve is open, said constant flow regulator having a flow resistance that changes in dependence on an applied pressure difference such that the substantially constant flow is independent of said pressure difference and results over a predefined operating range.

2. The dialysis machine in accordance with claim 1, wherein the constant flow regulator comprises: a housing which is flowed through by fluid and which has an inlet, a regulator opening and an outlet; a plunger which is displaceably arranged in the housing, with a regulator passage remaining between the regulator opening and the plunger which is dependent on a relative position between the plunger and the regulator opening and which defines a regulation effect; and a spring against whose force the plunger is displaced by a differential pressure between the inlet and the outlet of the housing.

3. The dialysis machine of claim 2, wherein a minimum flowed-through cross-section of the regulator passage changes on a displacement of the plunger relative to the regulator opening.

4. The dialysis machine of claim 3, wherein both a length of the regulator passage and the minimum flowed-through cross-section of the regulator passage changes on the displacement of the plunger relative to the regulator opening.

5. The dialysis machine of claim 3, wherein at least one of the minimum flowed-through cross-section of the regulator passage reduces as the differential pressure increases, and a length of the regulator passage increases as the differential pressure rises.

6. The dialysis machine of claim 3, wherein at least one of a cross-sectional surface and a diameter of the plunger reduces progressively, i.e. at an increasing rate, in a direction of flow in a first part region, with a step region adjoining the first part region in the direction of flow.

7. The dialysis machine of claim 6, wherein the diameter of the plunger reduces at a rate which becomes smaller or does not reduce at all in the step region.

8. The dialysis machine of claim 6, further comprising at least one of: the first part region ends before the regulator opening in an end position of the plunger without differential pressure; the first part region ends before a narrowest point of the regulator opening in an end position of the plunger without differential pressure; the step region extends partly within the regulator opening and partly before the regulator opening in an end position of the plunger without differential pressure; and the step region extends at both sides of the narrowest point of the regulator opening in an end position of the plunger without differential pressure.

9. The dialysis machine of claim 3, wherein the plunger is pressed against an abutment by the spring on an absence of differential pressure, with a flow through or past the plunger being blocked in this position.

10. The dialysis machine of claim 9, wherein the flow through or past the plunger is blocked by a seal.

11. The dialysis machine of claim 2, wherein the regulator opening is tubular, with at least one of a cross-sectional surface and a diameter of the tubular regulator opening increasing in a part region in a direction of flow, and with at least one of a smallest cross-sectional surface and a smallest diameter being arranged at a side of the regulator opening facing the inlet.

12. The dialysis machine of claim 2, wherein the plunger is connected to a guide region which contacts an inner wall of a guide chamber of the housing and is slidingly guided in the guide chamber on the inner wall.

13. The dialysis machine of claim 1, wherein the constant flow regulator has a substantially constant flow between 500 ml/min and 3000 ml/min.

14. The dialysis machine of claim 2, wherein the housing comprises a first part and a second part which are screwed or adhesively bonded to one another, said first part including a guide chamber, the regulator opening and the outlet; and the second part including the inlet.

15. The dialysis machine of claim 14, wherein the second part includes a sealing structure against which the plunger is pressed by the spring on an absence of differential pressure.

16. The dialysis machine of claim 6, wherein a length of the step regions amounts to less than 50% of an adjustment path of the plunger and a length of the first part region amounts to more than 50% of the adjustment path of the plunger.

17. The dialysis machine of claim 12, wherein an abutment for the plunger is formed by an end of the guide chamber at an inlet side against which the guide region is pressed on an absence of differential pressure, with the guide chamber having a larger diameter than the regulator opening.

18. The dialysis machine of claim 1, wherein an operating pressure range of the constant flow regulator includes at least one of differential pressures between 0.5 bar and 5.5 bar, and inlet pressures between 1.5 bar and 6 bar.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will now be described in more detail with reference to embodiments and to drawings.

(2) There are shown:

(3) FIG. 1: a dialysis machine in accordance with the prior art;

(4) FIG. 2: an embodiment of a dialysis machine in accordance with the invention in accordance with the first aspect of the present invention;

(5) FIG. 3: an embodiment of a constant flow regulator in accordance with the invention in accordance with the first variant of the second aspect of the present invention;

(6) FIG. 4: a diagram which shows the minimum flowed-through cross-section of the regulator passage in dependence on a differential pressure in the embodiment shown in FIG. 3;

(7) FIG. 5: a schematic representation for illustrating the minimum flowed-through cross-section of the regulator passage in accordance with the invention changed a displacement of the plunger relative to the plunger opening;

(8) FIG. 6: a diagram which shows the influence of differences of the plunger geometry from an optimum desired geometry on the flow through the constant flow regulator in the embodiment shown in FIGS. 3 and 4;

(9) FIG. 7: the shape of a plunger for the constant flow regulator in accordance with a preferred embodiment of the first variant of the second aspect of the present invention together with a schematic representation of the flow produced hereby in dependence on the differential pressure; and

(10) FIG. 8: a further embodiment of a constant flow regulator in accordance with the invention in which the first and second variants of the second aspect are implemented in combination.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(11) Further scope of applicability of the present invention will become apparent, from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

(12) FIG. 2 shows an embodiment of a dialysis machine 10 in accordance with the invention. The dialysis machine has a water inlet 11 with which it can be connected to an external water supply at the installation site. The external water supply can, for example, be an RO ring line, an individual position and/or a reverse osmosis plant. The dialysis machine has a dialyzate system 12 which is only shown schematically in FIG. 2, which has an inlet chamber 14 which can be filled with water via the water inlet 11. For this purpose, the water inlet 11 is connected to the inlet chamber 14 of the dialyzate system 12 via a line 16.

(13) A constant flow regulator 13 is provided in accordance with the invention in the line 16 between the water inlet 11 and the inlet chamber 14 of the dialyzate system. It is designed as a passive flow control element such that it changes its flow resistance in dependence on the pressure difference between the water inlet and the inlet chamber such that an approximately constant flow is adopted over the total operating range. A regulation element is in particular provided which is displaced against the force of a spring by the applied pressure difference between the inlet and the outlet of the constant flow regulator and hereby changes the flow resistance of the constant flow regulator. The regulation element can in particular be a plunger which cooperates with a restrictor opening of the constant flow regulator.

(14) The operating pressure range of the constant flow regulator comprises inlet pressures between 1.5 bar and 6 bar in the embodiment. The constant flow regulator is configured such that it sets a substantially constant flow between 1000 ml/min and 1500 mil/min over the total operating pressure range. A substantially constant flow in the sense of the present invention preferably does not differ from a maximum flow by more than 35%, preferably not by more than 20%.

(15) As further shown in FIG. 2, the inlet chamber 14 of the dialyzate system 12 has a level sensor 17 which is connected to a control 18 of the dialysis machine. An inlet valve 15 is furthermore provided in the line 16 downstream of the constant flow regulator 13. The control controls the inlet valve 15 in dependence on the data of the level sensor 17 to fill the inlet chamber 14. The inlet vale 15 is preferably a switching valve.

(16) A heat exchanger 19 via which the water flowing into the inlet chamber 14 can be heated is furthermore provided in the line 16 downstream of the constant flow regulator 13.

(17) The dialysis machine is preferably a device for hemodialysis and/or hemofiltration. An extracorporeal blood circuit is therefore connectable to the dialysis machine which is typically configured as a disposable. A dialyzer is arranged in the extracorporeal blood circuit which, on the one hand, forms a part of the extracorporeal blood circuit and, on the other hand, is connected to the dialyzate system of the dialysis machine. During a dialysis treatment carried out by the dialysis machine, blood and dialyzate flow through the two halves of the dialyzer which are separated from one another via a membrane in order thus to enable a mass transfer between the dialyzate and the blood. The dialysis machine can in particular have a blood pump and/or a dialyzate pump which is/are controlled by the control 18.

(18) Any desired constant flow regulators can initially be used within the framework of the dialysis machine in accordance with the invention. However, constant flow regulators are preferably used which will be described in more detail in the following.

(19) The constant flow regulators described in the following cannot only be used for dialysis machines, but also in other applications, for example in other medical devices.

(20) FIG. 3 shows a first embodiment of a constant flow regulator in accordance with the invention. The constant flow regulator comprises a housing 20 having an inlet 21, a guide chamber 22, a regulator opening 23 and an outlet 24. A plunger 25 is displaceably arranged in the housing; it cooperates with the regulator opening 23 and hereby produces the regulation effect of the constant flow regulator.

(21) The inlet 21 and the outlet 24 of the housing are each led out of the housing in tubular form so that a respective hose nozzle can be pushed onto the inlet 21 and onto the outlet 24. The inlet 21 and the outlet 24 have a smaller outer diameter for this purpose than the middle part of the housing. The outer surfaces of the tubular section forming the inlet 21 and the outlet 24 each have a cylindrical section 35 to which a clip can be attached and also each have a bead 36 which prevents a removal of the hose nozzle after the attachment of the clip.

(22) The plunger is arranged at a guide region 26 which is displace ably guided in the guide chamber 22. The guide region has a cylindrical outer contour which contacts the likewise cylindrical inner contour of the guide chamber 22 and is guided at it.

(23) The regulator opening is formed by a tubular section 37 of the housing which adjoins the guide chamber 22 and which has a smaller diameter than the guide chamber itself and/or is formed by the narrowest point 32 of this section. The plunger 25 is of pin shape and extends axially from the guide region 26 to the regulator opening. Depending on the position of the guide region 26, the plunger is pushed into the tubular section 37 by different amounts or is moved by different amounts relative to its narrowest point. A regulator passage which is depending on the relative position between the plunger and the regulator opening and which defines the regulation effect is hereby produced between the inner contour of the regulator opening 23 or 32 and the outer contour of the plunger element 25.

(24) A spring 28 is arranged in the guide chamber 22; it extends between the end of the guide chamber 22 at the outlet side and the end of the guide region 26 at the outlet side and preloads the plunger against the direction of flow.

(25) The guide region 26 in the embodiment has a plurality of passage bores 27 through which liquid can flow substantially without any regulation effect. The guide chamber itself has no relevant regulation effect due to the increased cross-section of the guide chamber 22. The flow resistance of the regulator is therefore defined by the regulator passage remaining between the regulator opening 23 or 32 and the plunger 25.

(26) The housing 20 in the embodiment is made up of two elements 29 and 30. The element 29 comprises the outlet 24, the regulator guide 23 or 32 and the guide chamber 22. The second element comprises the inlet 21 as well as an abutment region 33 against which the guide region 26 of the plunger is pressed by the force of the spring 28 in the case of an absence of differential pressure. Both housing elements each have a flange region in which they are screwed together by screws 31. In this respect, a sealing element 34, a sealing ring in the embodiment, is provided which seals the two housing elements with respect to one another. The housing elements and the plunger are preferably designed as injection molded plastic parts. The first housing element 29 is preferably produced from a translucent and/or transparent material to be able also to visually check the function of the constant flow regulator.

(27) In the embodiment, the regulator passage is configured as an annular gap which extends between the outer periphery of the plunger and the inner periphery of the regulator opening. In the embodiment, the regulator opening and the plunger have a rotationally symmetrical contour and are arranged coaxially.

(28) The regulator opening 23 can have a constant diameter in a possible embodiment.

(29) In the embodiment, the diameter of the tubular section comprising the regulator opening in contrast expands in funnel-like shape in the direction of flow. The expansion is, however, only slight, with the expansion of the cross-sectional surface of the tubular section in the embodiment amounting to a maximum of 10% over the total movement range of the plunger starting from the narrowest point 32. In the embodiment, the section 23 comprising the regulator opening merges directly into the outlet 24 of the constant flow regulator.

(30) The narrowest point 32, i.e. the point with the smallest cross-sectional surface or the smallest diameter of the regulator opening 23 is provided at the side of the regulator opening 23 at the inlet side in the embodiment. This point therefore defines together with the diameter of the plunger 25 at this point the minimally flowed-through cross-section of the regulator passage. Despite the only small expansion of the passage, the actually effective regulation arises in a possible embodiment essentially only at this narrowest point 32 so that only it acts as a regulator opening.

(31) In this respect, the cross-sectional surface or the diameter of the plunger changes in the region which is led past the narrowest point 32 on a movement of the plunger. The cross-sectional surface or the diameter of the plunger in particular reduces in the direction of flow in this respect. The minimum flowed-through cross-section of the regulator passage remaining between the plunger 25 and the regulator opening 23 hereby depends on the relative position between the plunger 25 and the regulator opening 23.

(32) In accordance with the invention, the plunger 25 is displaced against the force of the spring 28 in the direction of flow by a pressure difference between the inlet 21 and the outlet 24. The minimum flowed-through cross-section of the regulation passage remaining between the plunger 25 and the regulator opening 23 is hereby changed. In a possible embodiment, the length of the regulator passage can also vary and can likewise be used for influencing the flow. The change in the cross-section and, optionally, in the length takes place such that an approximately constant flow results.

(33) In the embodiment shown in FIG. 3, the tip of the plunger is in the region of the narrowest point 32 of the regulator opening in the situation of the constant flow regulator shown in FIG. 3 without differential pressure. In this starting position, the very short regulator passage remaining between the tip of the plunger and the narrowest point of the regulator opening behaves as an annular gap diaphragm. The flow amount is determined by the orifice area A of the regulator passage, i.e. by the minimally flowed-through cross-section of the regulator passage.

(34) The constant flow regulator in accordance with the invention is designed such that the minimum flowed-through cross-section and thus the orifice area A of the regulator passage vary in dependence on the pressure difference. It is effected by a corresponding shape of the plunger.

(35) The minimally flowed-through cross-section of the regulator passage in the embodiment shown in FIG. 3 is shown in dependence on the differential pressure in FIG. 4. As can immediately be seen from FIG. 4, the highest changes of the cross-sectional surface occur at low differential pressures.

(36) Since low pressure differences can occur over the constant flow regulator despite a sufficient inlet pressure by flow resistances downstream of the constant flow regulator such as a heat exchanger, this operation region is actually also relevant on a use in a dialysis machine.

(37) The relationship shown in FIG. 4 between the cross-sectional surface of the constant flow regulator and the differential pressure requires a shape of the plunger in which the diameter of the plunger progressively reduces in the direction of flow or in the direction of movement of the plunger as the differential pressure increases. This means that the diameter reduces, and indeed at a rate increasing in the direction of flow.

(38) The relationships can be derived as follows from the orifice formula. In accordance with the orifice formula, the following relationship results between the flow Q which is to be set to a constant value and the orifice area A of the diaphragm, the differential pressure ΔP between the inlet pressure P1 and the outlet pressure P3 (i.e. ΔP=P1−P3) and the viscosity ρ and a coefficient α:

(39) $Q=\alpha A\sqrt{\frac{2}{\rho }\left(\Delta P\right)}=\mathrm{const}.$

(40) The resulting orifice area A in dependence on the differential pressure ΔP is obtained from the conversion of the formula:

(41) $A=\frac{Q}{\alpha \sqrt{\frac{2}{\rho }\left(\Delta P\right)}}$

(42) The differential pressure acts on the cross-sectional surface of the plunger in the orifice area of the constant flow regulator, i.e. in the embodiment shown in FIG. 3 in the region of the narrowest point 32 of the regulator opening. The plunger is moved so far in dependence on the differential pressure until the spring force and the force effect produced by the differential pressure on the plunger are in equilibrium. The position x of the plunger therefore depends as follows on the spring stiffness R and on the cross-sectional surface A of the plunger in the orifice area:

(43) $x=\frac{F}{R}=\frac{\Delta P*A_i}{R}$

(44) As shown schematically in FIG. 5, the orifice area A is the remaining area of the regulator opening which is not blocked by the plunger. In this respect A.sub.0 is the minimal cross-sectional surface of the regulator opening defined by the minimal diameter d.sub.0 and A.sub.i is the cross-sectional surface of the plunger in the region of the narrowest point 32 given by the diameter d.sub.1 of the plunger at the position x.

(45) The diameter of the plunger d.sub.1 at the position x is therefore given by the difference from the constant outer diameter do of the narrowest point of the regulator opening which is predefined by the housing and the diaphragm area required in accordance with the above formula. In this respect, the following applies to the orifice area A which is used in formulas 1 and 2:

(46) $A=A_0-A_i=\frac{\pi }{4}\left(d_0^2-d_i^2\right)$

(47) The following dependence of the diameter d.sub.i of the plunger on the position x hereby results:

(48) $d_i\left(x\right)=\sqrt{\frac{4A_0}{\pi }+\frac{Q^2\rho }{2{\alpha }^2\pi \mathrm{Rx}}}-\frac{2Q}{\alpha \sqrt{\frac{8\pi \mathrm{Rx}}{\rho }}}$

(49) Since the force acting on the surface A.sub.i through the differential pressure ΔP is in a linear relationship with the position x, a curve is essentially produced for the progression of the diameter d.sub.i in dependence on the position x which corresponds to the inverse progression of the orifice area A shown in FIG. 4. The diaphragm surface thus changes to a very high degree over the first millimeters. This initial region corresponds to the operating point at small differential pressure.

(50) The inventor of the present invention has now recognized that tolerances of the plunger diameter and of the spring length can produce large deviations of the flow in this critical region. Flows which are too high in particular arise in the low differential pressure range when the plunger surface is too low due to production tolerances or when the plunger covers too small a distance due, for example, to sticking friction and/or to a spring which is too stiff or too long. FIG. 6 shows a simulation result which represents the deviation from a desired flow in dependence on tolerances.

(51) It can be seen in FIG. 6 that with tolerances in the direction of too large a diaphragm surface the deviation in the flow is substantially more dramatic than with the same tolerances in the direction of too small a flow.

(52) In the further embodiments of a constant flow regulator in accordance with the invention shown in FIGS. 7 and 8, measures have therefore been taken to reduce such great deviations in the direction of high flows and thus to make the constant flow regulator more robust with respect to production tolerances and factors of influence such as sticking friction, etc.

(53) FIG. 7 shows an alternative geometry for the plunger tip. In this respect, the geometry of the plunger differs from the above-described ideal line of the orifice equation in the region of the tip, and indeed in the direction toward larger diameters. For this purpose, instead of the great reduction in the diameter at the position x=0, i.e. at that point which is arranged in the position without differential pressure in the region of the narrowest point 32 of the regulator passage, a step 40 is provided construction-wise which prevents the diameter d.sub.i from falling below a certain value. The diagram in FIG. 5 shows in an exaggerated manner the effect of this step or edge on the flow. A region 41 in which the diameter d.sub.i follows the ideal line and thus progressively decreases in the direction of flow, i.e. against the arrow indicating the position x, then adjoins the step region 40. Conversely, the diameter d.sub.i increases degressively in the region 41 in dependence on the position x. The region with the greatest change of the diameter d.sub.i is therefore that one which directly adjoins the step region 40.

(54) In the embodiments shown, the position x defines that position of the plunger which is located in the region of the point 32 having the narrowest diameter of the regulator opening. The above-named relationships can, however, alternatively also be defined in relation to the inlet of the regulator opening. This is in particular the case when the regulator opening has a constant diameter.

(55) Furthermore, as shown in FIG. 8, the risk of an absent deflection due to sticking friction or too stiff/long a spring is prevented construction-wise. For this purpose, the plunger has a seal at the rear side of the guide element 26 which is pressed against the end of the guide chamber at the inlet side by the spring in the position without differential pressure, with the seal being able to comprise an elastomer, for example. The end of the guide chamber at the inlet side is equipped with a sealing geometry 44, in the embodiment with a sealing bead surrounding the inlet 21 and which is pressed against the seal 43 at the plunger. A flowing through of the flow bores 27 of the guide region 26 is hereby prevented in the position without differential pressure and equally a flowing around of the guide region. This arrangement has the result that the plunger has to be moved to release the flow path. It is hereby ensured that small pressure differences are sufficient to overcome the sticking friction. It is a further advantage of this arrangement that the constant flow regulator has been supplemented by a non-return function.

(56) The dialysis machine in accordance with the present invention has the advantage that the feed flow of water into the dialysis system of the machine is regulated automatically. A manual setting of the pressure as currently on the putting into operation is thus no longer necessary. Furthermore, an inexpensive and simple design is ensured. In this respect, the constant flow regulator is a passive component which is service-free.

(57) The constant flow regulators in accordance with the invention in accordance with the second aspect of the present invention are optimized for low differential pressures and high flow precision. The second variant furthermore has an integrated check valve function.

(58) The invention being thus described, it will be apparent that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be recognized by one skilled in the art are intended to be included within the scope of the following claims.