Method and system for pumping two liquids in equal quantities in an artificial kidney

A method and a system of pumping a first and a second liquid in an artificial kidney in substantially equal quantities at a substantially constant flow. The system includes a main pump having complementary main chambers, and first and second auxiliary pumps each having complementary auxiliary chambers. The pumps are reciprocated in unison and the system further includes a unique configuration of intake and discharge lines and associated control valves which provide a constant and equal flow of first and second liquid into and out of the artificial kidney during reciprocation of the pumps in both directions.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to artificial kidneys, and more particularly, 
to a method and system for pumping two liquids in equal quantities and 
with a continuous flow rate in two separate conduits of an artificial 
kidney. 
2. Description of the Related Art 
Artificial kidneys typically pump two liquids, for example, fresh and used 
dialysis liquid, into and out of a hemodialyser. An example of a known 
apparatus for pumping the two liquids is illustrated in FIG. 1 and 
includes, a pumping device 106 having two complementary chambers 112 and 
113 associated with four valves 126, 127, 128 and 129, disposed, 
respectively, in lines 118, 119, 121 and 120. The operation of such a 
device is effected over two periods. During the first period, the valves 
126 and 127 are closed, and valves 128 and 129 are open. A reciprocating 
piston 109, separating the two complementary chambers 112 and 113, is 
moved in direction A so as to aspirate a first liquid into chamber 112, 
and, at the same time, discharge an equal quantity of a second liquid from 
chamber 113. In the second period, valves 128 and 129 are closed, and 
valves 126 and 127 are open, and piston 109 is moved in direction R to 
discharge from chamber 112 a quantity of the first liquid into line 118, 
and to simultaneously aspirate a quantity of the second liquid into 
chamber 113 from line 119. 
With the device depicted in FIG. 1, it is possible to pump two liquids in 
substantially equal quantities in two separate conduits, but the flows in 
the four lines 118, 119, 120 and 121, are discontinous due to the 
alternating movement of piston 109 during reciprocation. 
To mitigate this drawback, apparatus have been proposed which, effectively, 
comprise two of the devices of FIG. 1 arranged in parallel. Such a system 
is illustrated in FIG. 2 and includes two pumping devices 206 and 206' 
having respective complementary chambers 212, 213 and 212', 213' 
associated with eight valves 226, 226'; 227, 227'; 228, 228'; and 229, 
229', disposed in respective conduits or lines connected to the chambers 
of pumping devices 206 and 206' as shown. 
Operation of the device of FIG. 2 is as follows. In a first period, valves 
226, 227, 228' and 229' are closed; and valves 228, 229, 226' and 227' are 
opened. A pair of reciprocating pistons 209 and 209', disposed in pumps 
206 and 206', respectively, are then moved in direction A. Movement of 
piston 209 in direction A aspirates the first liquid into chamber 212 from 
an intake line 220, and discharges the second liquid from chamber 213 into 
an outlet line 221. Simultaneously, movement of piston 209' in direction 
A, discharges the first liquid from chamber 213' into an outlet line 218, 
and aspirates the second liquid into chamber 212' from an intake line 219. 
In a second period, valves 226, 227, 228' and 229' are opened, and valves 
228, 229, 226' and 227' are closed. Reciprocating pistons 209 and 209' are 
then moved in direction R. Piston 209' upon being moved in direction R, 
aspirates the first liquid into chamber 213', and discharges the second 
liquid from chamber 212' into line 221. Simultaneously, movement of the 
piston 209 in direction R aspirates the second liquid into chamber 213 
from line 219, and discharges the first liquid from chamber 212 into line 
218. 
By means of systems such as illustrated in FIG. 2, substantially continuous 
flow through lines 218, 219, 220, 221 can be attained. 
A system similar to the one described above with reference to FIG. 2 is 
described in German Patent Application DOS 2 634 238. However, the 
embodiments of the device disclosed in that German patent utilize elastic 
members disposed in respective chambers rather than reciprocating pistons. 
The circulation of the fresh and used dialysis liquid comprising the first 
and second liquids is accomplished by two pumps displacing the membranes 
in the chambers to displace the dialysis liquid. 
In principle, these prior art systems allow two liquids in two separate 
conduits to be pumped in substantially equal quantities and with a 
substantially continuous flow. However, small errors occur each time the 
valves (226, 227, 228, 229, 226', 227', 228', 229') are opened or closed. 
With a high frequency of opening and closing of the valves, the 
accumulation of these small errors leads to an even higher overall error. 
It is therefore an object of the present invention to provide a method and 
an apparatus for pumping equal quantities of two liquids through two 
separate conduits in which the errors associated with the valves opening 
and closing are substantially reduced. 
Additional objects and advantages of the invention will be set forth in the 
description which follows, and in part will be obvious from the 
description, or may be learned by practice of the invention. The objects 
and advantages of the invention may be realized and attained by means of 
the instrumentalities and combinations particularly pointed out in the 
appended claims. 
SUMMARY OF THE INVENTION 
A system is provided for pumping a predetermined quantity of a first liquid 
from a source through the outlet of a discharge line to be attached to an 
appliance such as a hemodialyser of an artificial kidney, and for pumping 
the same quantity of a second liquid from an intake line inlet into 
evacuation means, with both liquids moving at a substantially equal and 
constant flow. The system comprises a main reciprocating pump means having 
first and second complementary main chambers, and first and second 
auxiliary reciprocating pump means. The first auxiliary pump means has 
first and second complementary auxiliary chambers, and the second 
auxiliary pump means has third and fourth complementary auxiliary 
chambers. A drive means is provided for reciprocating the main pump means 
and the first and second auxiliary pump means in unison between a first 
and second direction such that the volume of the first main chamber varies 
inversely with the volume of the second and fourth auxiliary chambers, and 
directly with the volume of the first and third auxiliary chambers. 
A first intake line means is provided for aspirating the predetermined 
quantity of the first liquid into the first main chamber from both the 
fourth auxiliary chamber and from a source of the first liquid during 
reciprocation of the pump means in the first direction, and for aspirating 
the quantity of the first liquid into the fourth auxiliary chamber from 
the source of the first liquid during reciprocation of the pump means in 
the second direction. A first discharge line means is provided for 
discharging the quantity of the first liquid into both the second 
auxiliary chamber and into a discharge line outlet during reciprocation of 
the pump means in the second direction, and for discharging the quantity 
of the first liquid into a discharge line outlet from the second auxiliary 
chamber during reciprocation of the pump means in the first direction. 
A second intake line means is provided for aspirating the quantity of the 
second liquid into the second main chamber from both an intake line inlet 
and the third auxiliary chamber during reciprocation of the pump means in 
the second direction, and for aspirating the quantity of the second liquid 
into the third auxiliary chamber from an intake line inlet during 
reciprocation of the pump means in the first direction. A second discharge 
line means is provided for discharging the quantity of the second liquid 
into both the first auxiliary chamber and a drain during reciprocation of 
the pump means in the first direction, and for discharging the quantity of 
the second liquid into the drain from the first auxiliary chamber during 
reciprocation of the pump means in the second direction. The above 
described system operates such that the same quantity of the first and 
second liquid moves in a substantially constant flow during reciprocation 
of the pump means in both the first and the second direction.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Reference will now be made in detail to the present preferred embodiments 
and method of the invention as illustrated in the accompanying drawings. 
In accordance with the present invention, and as illustrated in FIG. 3, 
there is provided pumping system for an artificial kidney. As embodied 
herein, the pumping system is hooked to a hemodialyser 1 separated into 
two compartments 3 and 4 by a semi-permeable membrane 2 permitting 
dialysis and ultrafiltration of the blood. First compartment 3 is intended 
for the extracorporeal circulation of the blood, and second compartment 4 
is intended for the circulation of the dialysis liquid flowing from a 
source 60, into the hemodialyser, then from the hemodialyser towards an 
evacuation means 62. As embodied herein, evacuation means 62 may include 
regeneration means. 
In accordance with the invention the system includes a main reciprocating 
pump means and first and second auxiliary reciprocating pump means. As 
embodied herein, the main pump means comprises a main pump 6, and the 
first and second auxiliary pump means includes auxiliary pumps 7 and 8, 
respectively. Main pump 6 comprises a cylinder 40 which is separated into 
complementary first and second main chambers 12 and 13 by a piston 9. Each 
auxiliary pump 7 and 8 includes a cylinder 46 and 48, respectively, which 
are separated into first, second, third, and fourth auxiliary chambers 14, 
15, 16, and 17, respectively, by a piston 10 disposed in cylinder 46 and a 
piston 11 disposed in cylinder 48. Each of the pistons is tightly sealed 
about its periphery in its respective cylinder. In the present preferred 
embodiment of the invention, pistons 10 and 11 are coaxial and fixedly 
connected to one another, and to main piston 9, by a rod 30. A drive 
means, which will be described hereinafter, is connected to rod 30 to move 
pistons 9, 10 and 11 in unison in a reciprocating motion between 
directions A and R. 
Main chamber 12 of pump 6 holds the fresh dialysis liquid and is connected 
to dialysis liquid source 60 and to fourth auxiliary chamber 17 by a first 
intake line means. As embodied herein, the first intake line means 
includes lines 20 and 23 and valve means 28 disposed in line 20. 
Main chamber 12 is also connected to an inlet 42 of hemodialyser 1 and to 
second auxiliary chamber 15 by a first discharge line means, which, as 
embodied herein comprises lines 18 and 24, and valve means 26 disposed in 
line 18. 
Main chamber 13 holds the used dialysis liquid and is connected to an 
outlet 44 of hemodialyser 1 and to third auxiliary chamber 16 by a second 
intake line means, which, as embodied herein comprises lines 19 and 25, 
and valve means 27 disposed in line 25. Main chamber 13 is also connected 
to an evacuation or regeneration means 62 for the used dialysis liquid and 
to first auxiliary chamber 14 by a second discharge line means, which, as 
embodied herein, comprises lines 21 and 22, and valve means 29 disposed in 
line 21. 
In each auxiliary pump 7 and 8, second and fourth auxiliary chambers 15 and 
17 cycle fresh dialysis liquid, and first and third auxiliary chambers, 14 
and 16, cycle the used dialysis liquid. 
Auxiliary chamber 14 is connected to line 21 downstream of valve means 29 
by line 22. Auxiliary chamber 15 is connected to discharge line 18 
downstream of valve means 26 by line 24. Auxiliary chamber 16 is connected 
to output line 19 upstream of valve means 27 by line 25. Auxiliary chamber 
17 is connected to intake line 20 upstream of valve means 28 by line 23. 
Auxiliary chambers 14 and 16 regulate the flow of the used dialysis liquid, 
while auxiliary chambers 15 and 17 regulate the flow of the fresh dialysis 
liquid. The design of pumps 6, 7 and 8 is selected such that simultaneous 
displacement of the pistons disposed therein displaces a quantity of 
liquid in each main chamber 12 and 13 which is twice the quantity of 
liquid displaced in each auxiliary chamber 14, 15, 16 and 17. In the case 
where pumps 6, 7, and 8 have a circular cross section, auxiliary pumps 7 
and 8 may be configured with a cross section equal to half the cross 
section of main pump 6. 
Operation of the apparatus illustrated schematically in FIG. 3 is discussed 
below. Rod 30 is connected to each piston 9, 10 and 11 and is driven in a 
rectilinear reciprocating motion by any type of suitable motor or drive 
menas schematically represented by 50 to reciprocate pistons 9, 10 and 11 
between a first direction represented by arrow A, and a second direction 
represented by arrow B. 
In a first stage called the aspiration stage, valve means 26 and 27 are 
closed, and valve means 28 and 29 are open. Rod 30 is driven such that 
pistons 9, 10 and 11 are displaced in the direction of arrow A. The 
displacement of the pistons in direction A draws fresh dialysis liquid 
into chamber 12 and ejects used dialysis liquid from chamber 13. One half 
of the dialysis liquid drawn into chamber 12 comes from the source of 
fresh dialysis liquid 60, through line 20 and valve 28, and one-half of 
the fresh dialysis liquid drawn into chamber 12 comes from auxiliary 
chamber 17 via lines 23, 20 and valve 28. 
With movement of pistons 9, 10 and 11 still in direction A, one-half of the 
dialysis liquid discharged from chamber 13 is drawn into auxiliary chamber 
14 via lines 21, 22 and valve 29 by simultaneous displacement of pistons 9 
and 10; and the other half of the dialysis liquid is discharged through 
line 21 and valve 29 to evacuation or regeneration means 60. Displacement 
of piston 10 in direction A simultaneously delivers the fresh dialysis 
liquid from auxiliary chamber 15 to hemodialyser 1 via lines 24 and 18 
since valve 26 is closed. Displacement of the piston 11 in direction A 
aspirates used dialysis liquid from hemodialyser 1 into auxiliary chamber 
16 via lines 19 and 25 since valve 27 is closed. 
In a second stage called the delivery stage, rod 30 is driven such that 
pistons 9, 10 and 11 are displaced in the direction of arrow R. Valve 
means 26 and 27 are open, and valve means 28 and 29 are closed. 
The decrease in volume of main chamber 12 by movement of piston 9 in 
direction R aspirates equal quantities of fresh dialysis liquid into 
auxiliary chamber 15 via lines 18, 24 and valve 26 on the one hand, and on 
the other hand, into hemodialyser 1 through line 18, valve 26, and first 
discharge line outlet 42. The increase in volume of chamber 13 and 
decrease in volume of chamber 16 by movement of pistons 9 and 11 in 
direction R aspirates used dialysis liquid into chamber 13 via outlet line 
19 and valve 27 from hemodialyser 1, and from chamber 16 into chamber 13 
via lines 19, 25 and valve 27. 
In effect, the movement of pistons 9, 10 and 11 in direction R discharges 
used dialysis liquid from auxiliary chamber 16 and simultaneously 
aspirates fresh dialysis liquid into auxiliary chamber 17 via line 20 and 
line 23. At the same time, used dialysis liquid from auxiliary chamber 14 
is discharged into line 21 from chamber 14 via line 22. 
The successive closing and opening of the valve means 26, 27, 28 and 29 in 
the sequence described above, as well as the change in the direction of 
displacement of rod 30 and pistons 9, 10 and 11, may be actuated by means 
of end of travel contacts integral with rod 30 and associated with a 
guidance system (not shown) of any known type, such as a microprocessor 
for controlling the sequential opening and closing of the valves. 
With reference to the graphs of FIGS. 4 and 5 illustrating the flows in the 
various lines, it will, on the one hand, be observed that the quantity of 
the fresh dialysis liquid, or first liquid, drawn into respective chambers 
is equal to the quantity of the used dialysis liquid, or second liquid, 
delivered into respective chambers by the pumping system according to the 
present invention, and, on the other hand, that the flows of the dialysis 
liquid are continuous in the lines 18 and 19, that is to say, at outlet 42 
and at inlet 44. 
All the graphs illustrated in FIGS. 4 and 5 indicate time on the x axis 
subdivided into successive aspiration and delivery stages of the system, 
and the flow, expressed in units of flow 0, +1, -1, and 2 on the y axis. 
For example, one may choose a flow unit to be equal to 500 ml/min. 
The graphs lines of FIG. 4 correspond to the variations of flow in the 
lines which deliver fresh dialysis liquid to hemodialyser 1, and the graph 
lines of FIG. 5 correspond to the variations of flow in the corresponding 
lines which expel the used dialysis liquid. 
Graph line 1 of FIG. 4 represents flow through line 20 upstream of the 
junction with line 23 and shows that the supply of fresh dialysis liquid 
is effected at a constant flow rate. Regardless of whether the system is 
in the aspiration stage or in the delivery stage, there is always one unit 
of flow in line 20 upstream from the junction with line 23. This unit of 
flow is delivered alternately, in accordance with the direction pistons 9 
and 11 are moved, to either first main chamber 12 or fourth auxiliary 
chamber 17, depending on whether valve 28 is open or closed. 
The graph line 2 represents the circulation in line 20 downstream from the 
junction with line 23. It will be seen that when valve 28 is open, that is 
to say, in the aspiration stage with pistons 9, 10 and 11 moved in 
direction A, the flow rate of the dialysis liquid is two units, one unit 
coming from auxiliary chamber 17 via line 23, and one unit coming from the 
dialysis liquid source 60. In the delivery stage of the apparatus, that 
is, movement of pistons 9, 10 and 11 in direction R, the flow in line 20 
is zero since valve 28 is closed. 
On the other hand, in graph line 3, it is seen that in line 18 upstream of 
the junction with line 24, the flow rate is zero in the aspiration stage 
since valve 26 is closed, and is equal to two units in the delivery stage 
with valve 26 open. The two units of flow in line 18 during the delivery 
stage are supplied from main chamber 12 as piston 9 moves in direction R. 
One unit of flow is delivered to auxiliary chamber 15 through line 24, and 
one unit is delivered through first discharge line outlet 42. 
The graph line 4 represents the flow rate in line 24. In the aspiration 
stage, the flow rate is a positive one unit, that is to say, the dialysis 
liquid flows from chamber 15 towards line 18 since valve 26 is closed, 
while in the delivery stage, the flow rate is a negative one unit in line 
24, the negative signifying that the liquid then flows from first main 
chamber 12 through lines 18 and 24 into auxiliary chamber 15 with valve 26 
open. 
The graph line 5 represents the flow rate of the dialysis liquid that 
passes through first discharge line outlet 42. It may be considered as the 
sum of the flow rates of the graph lines 3 and 4. It will then be seen 
that the flow rate at outlet 42 is continuous and equal to the flow 
provided by the source of the fresh dialysis liquid. During movement of 
pistons 9, 10 and 11 in direction R, one unit of flow is delivered to 
first discharge line outlet 42 from first main chamber 12, and during 
movement of the pistons in direction A, one unit of flow is delivered to 
outlet 42 from second auxiliary chamber 15. 
Referring to the graph line 6 of FIG. 5, it will be seen that the flow rate 
of the used dialysis liquid through inlet 44 of second intake line 19 from 
the hemodialyser, upstream from the junction of line 25 is continuous and 
equal to one unit. This flow may be considered to be the sum of the flows 
of the graph line 7 and of graph line 8 described below. 
The graph line 7 represents the flow rate of the dialysis liquid in line 
25. In the aspiration stage, that is, movement of the pistons in direction 
A, the flow rate is a positive one unit, that is the liquid flows from 
inlet 44 through line 19 towards auxiliary chamber 16 since valve 27 is 
closed, while in the delivery stage the flow rate is a negative one unit, 
that is, the liquid flows from auxiliary chamber 16 into main chamber 13 
since valve 27 is open. 
The graph line 8 represents the flow rate in line 19 downstream from the 
junction with line 25. In the aspiration stage, that is to say when the 
valve 27 is closed and the pistons are moved in direction A, the flow rate 
is zero; and in the delivery stage, that is to say when the valve 27 is 
open and the pistons are moved in direction R, the flow rate is equal to 
two units, one unit coming from auxiliary chamber 16 via line 25 and one 
unit coming from hemodialyser 1 through line 19. 
The graph line 9 represents the flow rate in line 21 upstream from the 
junction with line 22. In the aspiration stage, that is to say when the 
valve 29 is open, the flow rate is equal to two units delivered from first 
main chamber 13 as piston 9 moves in direction A. In the delivery stage, 
that is to say when the valve 29 is closed, the flow rate is zero. 
The graph line 10 represents the flow rate in line 21 downstream from the 
junction with the line 22, this is, the flow of the used dialysis liquid 
directed to the evacuation or regeneration means 62. The flow rate in line 
21 downstream of the junction with line 22 is continuous and equal to 1 
unit. During movement of pistons 9, 10 and 11 in direction A with valve 29 
open, one unit is delivered from main chamber 13, and during movement of 
the pistons in direction R with valve 29 closed, one unit is delivered 
from first auxiliary chamber 14. 
A comparison of the graph lines 1 and 10 shows that the quantity of liquid 
entering the system through line 20 is equal to the quantity of liquid 
emerging from the system through line 21. Furthermore, the graph lines 5 
and 6, representing the circulation of the dialysis liquid in lines 18 and 
19, respectively, demonstrate that the dialysis liquid passes through 
hemodialyser 1 in a continuous flow. 
The quantity of the dialysis liquid drawn in and delivered during each 
successive aspiration and delivery stage depends on the amplitude or 
stroke of piston 9. The total quantity of the dialysis liquid passing 
through the circuit during the treatment session as a whole, depends on 
the value of the flow rate and hence on the frequency of the aspiration 
and delivery stages, that is to say, on the speed at which the rod 30 is 
driven. 
With continued reference to FIG. 3, an ultrafiltration pump 31 may be 
provided to draw off a quantity of dialysis liquid which is equal to the 
quantity of liquid which one wishes to eliminate from the patient's blood 
by ultrafiltration. 
In fact, in the case where the dialysis liquid circuit is a non-deformable, 
closed circuit, any quantity of liquid withdrawn from the dialysis liquid 
circuit produces a low pressure in the circuit which creates a pressure 
gradient at the level of the hemodialyser on either side of membrane 2. 
This pressure gradient causes a quantity of ultrafiltrate from the 
patient's blood to pass across semi-permeable membrane 2 of hemodialyser 
1. This quantity of ultrafiltrate is equal to the quantity of liquid 
withdrawn from the dialysis liquid circuit. 
The dialysis liquid can be withdrawn from line 19, upstream from the 
junction with line 25, as represented in FIG. 3, but may also be withdrawn 
from line 18 downstream from the junction with line 24. 
Although not represented in the drawings, provision may moreover be made in 
the dialysis liquid circuit for degassing devices, pressure transducers or 
flow detectors or any other accessory which is non-critical as far as the 
present invention is concerned. 
According to a second preferred embodiment of the invention illustrated in 
FIG. 6, auxiliary pumps 7 and 8 are no longer disposed coaxially with main 
cylinder 6. The pistons are not driven by means of a single rod, but, for 
instance, by means of three rods 30a, 30b, 30c linked to a rod 30 which is 
driven in a rectilinear reciprocating motion by any known means familiar 
to one skilled in the art such as an electromagnetic motor. 
In the case where, as illustrated in FIG. 6, the pumps 6, 7 and 8 are 
comprised of cylinders having a circular cross section, pistons 10 and 11 
are preferably configured with a cross section having a surface area equal 
to half the surface area of the cross section of piston 9. Thus, when 
pistons 10 and 11 are driven with the same motion and the same amplitude 
as piston 9, the quantity of the liquid displaced in each of main chambers 
12 and 13 is twice the quantity of liquid displaced simultaneously in each 
one of auxiliary chambers 14, 15, 16 and 17. 
FIG. 6 illustrates, moreover, that the functions of the auxiliary chambers 
15 and 17 may be reversed. In effect, according to this embodiment of the 
invention, chamber 15, complementary to chamber 14, is connected by a line 
23 to aspiration line 20 for the first liquid. Auxiliary chamber 17, 
complementary to the auxiliary chamber 16, is connected by a line 24 to 
the delivery line 18 for the first liquid. In the same manner, it is 
possible to reverse the functions of the chambers 14 and 16 with respect 
to aspiration and delivery stages of each as compared to the embodiment of 
the invention illustrated in FIG. 3. 
The circuit diagram of FIG. 7 illustrates another relative arrangement of 
auxiliary chambers 14, 15, 16 and 17. In this case, auxiliary pistons 10 
and 11 are displaced at the same time and with the same amplitude as 
piston 9, but in opposite directions. Thus, when main piston 9 is 
displaced in the direction of arrow A, auxiliary pistons 10 and 11 are 
displaced in the direction of arrow R and vice versa. This relative motion 
may be obtained, for instance, by means of mechanisms using crank 
connecting rod systems. 
In the embodiment of FIG. 7, auxiliary chamber 14 is connected by a line 22 
to delivery line 21, downstream from valve 29. Auxiliary chamber 15, which 
is complementary to auxiliary chamber 14, is connected by a line 23 to 
aspiration line 20 upstream from valve 28. Auxiliary chamber 16 is 
connected by a line 25 to aspiration line 19, upstream from valve 27, and 
auxiliary chamber 17, which is complementary with auxiliary chamber 16, is 
connected by a line 24 to delivery line 18. The operation of the device 
according to this mode of embodiment is as follows. 
In the aspiration stage, valves 26 and 27 are closed and valves 28 and 29 
are open. Main piston 9 is displaced in the direction of arrow A and 
auxiliary pistons 10 and 11 are displaced in the direction of arrow R. 
The increase in volume of main chamber 12 entails aspiration of the first 
liquid into chamber 12, one-half of the first liquid entering chamber 12 
coming from aspiration line 20, and one-half from chamber 15 via line 23. 
The simultaneous decrease in volume of main chamber 13 entails the 
delivery of an equal volume of the second liquid from chamber 13, one-half 
into chamber 14 via line 22 and one-half into the evacuation or 
regeneration means via line 21. Simultaneously, movement of the piston 11 
in direction R delivers the first liquid from auxiliary chamber 17 into 
delivery line 18 via line 24 and draws the second liquid coming from the 
aspiration line 19 into auxiliary chamber 16 via line 25. 
In the delivery stage, valves 26 and 27 are open and valves 28 and 29 are 
closed. Piston 9 is displaced in the direction of arrow R and pistons 10 
and 11 are displaced in the direction of arrow A. 
The first liquid which is expelled from main chamber 12 by piston 9 moving 
in direction R is delivered into auxiliary chamber 17 via line 24, and 
into delivery line 18. The increase in volume of main chamber 13 entails 
the aspiration of the second liquid into chamber 13, one-half of the 
volume of liquid entering chamber 13 coming from auxiliary chamber 16 via 
line 25, and one-half from aspiration line 19. Simultaneously, movement of 
the piston 10 in direction A entails delivery of the second liquid from 
auxiliary chamber 14 towards the delivery line 21 via line 22, as well as 
aspiration of the first liquid into the chamber 15 from aspiration line 20 
via line 23. 
The embodiment of the present invention illustrated in FIG. 7 makes it 
possible to pump equal quantities of a first and a second liquid while 
maintaining a continuous flow in aspiration lines 19 and 20, and in 
delivery lines 18 and 21. 
Many variations of the embodiments described and illustrated are within the 
grasp of one skilled in the art without thereby departing from the scope 
of the present invention. Thus the drive means of the pistons may be 
mechanical drive, but may also be a magnetic, electromagnetic or hydraulic 
drive. 
With reference to FIG. 3, in the case of a hydraulic drive, that is to say, 
by means of pumps for example, one pump may be disposed in aspiration line 
20 for the first liquid upstream from the junction with line 23, and one 
pump may be disposed in aspiration line 19 for the second liquid upstream 
from the junction with line 25. In this arrangement pumping device 6 no 
longer performs a motor function for the pumping. It is also possible, 
while remaining within the scope of the present invention, to replace the 
pistons by leakproof membranes or diaphragms. 
Valves 26, 27, 28 and 29 are preferably control valves, such as 
electrovalves. However, these valves need not be control valves but may be 
replaced by any type of conventional obturating device, such as one-way 
valves. However, when using one-way or check valves in combination with 
hydraulic drives, there would be the risk of the first liquid continuously 
passing from aspiration line 20 towards delivery line 18, and the further 
risk of the second liquid passing from aspiration line 19 towards delivery 
line 21. The set of four valves 26, 27, 28 and 29 may also be replaced by 
any equivalent means such as a distributor allowing a selection of the 
lines of passage for the dialysis liquid. 
In the modes of embodiment represented in FIGS. 3, 6 and 7, a cylindrical 
shape with a circular cross section was adopted for the cylinder of pumps 
6, 7 and 8, with the area of the cross section of main cylinder 40 being 
twice the area of the cross section of each of the auxiliary cylinders. It 
is, however, possible to choose a non-circular cross section for the 
auxiliary cylinders, and accordingly modify the amplitude of the movement 
of the auxiliary pistons so that the quantity of the liquid simultaneously 
displaced in each of the corresponding auxiliary chambers with 
displacement of auxiliary pistons 10 and 11 is one-half the quantity of 
liquid displaced in each main chamber by main piston 9. 
It is also possible that one or more of the cylinders of pumps 6, 7 and 8 
be divided into two complementary chambers by means of an equalizer system 
designed in such a way that the two associated chambers should be 
complementary to each other. 
Among the possible applications of the method and of the apparatus 
according to the present invention, there has been described the pumping 
of equal quantities of a fresh dialysis liquid and of a used dialysis 
liquid, as illustrated with reference to FIG. 3. 
However, the objects of the present invention may also be attained within 
the framework of haemofiltration with reinjection. In fact, in that 
technique, the quantity of the liquid withdrawn from the blood by 
ultrafiltration is replaced, save for the adjustment of the patient's 
weight, by an equal quantity of a substitution liquid which is injected 
into the blood. The first liquid pumped is then the ultrafiltrated liquid 
and the second liquid is the substitution liquid. 
Additional advantages and modifications will readily occur to those skilled 
in the art. Therefore, the invention in its broader aspects is not limited 
to the specific details, representative devices, and illustrative examples 
shown and described. Accordingly, departures may be made from such details 
without departing from the spirit or scope of the general inventive 
concept as defined by the appended claims and their equivalents.