The present invention relates to a metering pump device for medical use comprising a pumping chamber, an annular pumping diaphragm the outer edge of which is secured to the said pumping chamber and the inner edge of which is secured to a central drive part that is more rigid than the said diaphragm, able to be displaced parallel to itself between an extreme return position and an extreme displacement position in its expulsion stroke and its intake stroke, respectively, these two positions lying one on each side of the plane containing the outer edge of the said annular diaphragm, the said pumping chamber comprising an inlet valve and an outlet valve which are respectively opened by a reduced pressure and by a raised pressure in the pumping chamber as a result of the movements of the said annular pumping diaphragm, the intake stroke of the said diaphragm resulting from the energy accumulated by the elastic deformation of the diaphragm during its expulsion stroke.
Pumps of this type are already known. Production of such a pump as a metering pump for medical use, particularly as a single-use perfusion pump, presents numerous problems that known diaphragm pumps are unable to overcome.
This pump needs to be accurate, and small while at the same time providing optimum flow rate, and needs to represent good value for money because it is not re-usable. The outlet valve of the pump has to provide safety against a free flow of liquid under a certain pressure, which is typically that of the column of liquid between a pouch of perfusion liquid and the pump, or the pressure resulting from accidental pressure applied to the pouch of liquid. Given this safety, the pumping diaphragm has to be able to withstand the working pressure, which is made up of a pressure to open the outlet valve that has to remain closed up to a pressure that is determined by safety standards, of a pressure drop in the downstream pipe and of a service pressure at the end of the downstream pipe.
The pumping diaphragm has to be able to take in the liquid by moving from its extreme displacement position to its extreme return position creating enough of a reduced pressure in the presence of the pressure drop in the upstream and downstream pipes of the pumping device and of the pressure threshold of the inlet valve.
This intake has to be achieved as quickly as possible in order to provide an optimum flow rate given the volume of the pumping chamber. However, in order to avoid shockwaves in the pipes, vaporization of the pumped liquid through a pressure drop greater than the vapour pressure of the liquid, and the effects of cavitation, the reduced pressure created by the return of the diaphragm must not be too great.
Admittedly, the pumping diaphragm could be connected to the actuator for a two-way drive. However, such a solution would make the single use more complicated and therefore more difficult to manufacture and would make it more difficult to fit into the drive device. This method of driving also allows great precision in the control of the position of the diaphragm, and therefore great precision in the flow rate.
Meeting all of these conditions, some of which oppose others, is therefore not straightforward.
It is an object of the present invention to provide a solution which is able, at least in part, to meet the aforementioned conditions.
To this end, the subject of the present invention is a metering pump device for medical use according to Claim 1.
The various specifics and advantages of the invention will become better apparent from reading the following description of two embodiments of the metering pump device that forms the subject of the invention which are given by way of examples and illustrated schematically in the attached drawings.
The metering pump device that forms the subject of the invention is illustrated very schematically in
Aside from the pumping diaphragm 1, this device comprises a pumping chamber 2 into which there open an upstream pipe 3 controlled by an inlet valve 4, a downstream pipe 5 itself controlled by an outlet valve 6. The pumping diaphragm 1 is intended to move between an extreme displacement position that reduces the volume of the pumping chamber 2, leading to a raised pressure able to open the outlet valve 6 and an extreme return position that induces a reduced pressure able to close the outlet valve 6 and to open the inlet valve 4.
It is a more particular object of the invention to determine how to produce a diaphragm that is able to meet a certain number of conditions.
In order to expel the liquid from the pumping chamber 2, a drive mechanism 7, here symbolically depicted by a pushrod, pushes against the pumping diaphragm 1 in the direction of the inside of the pumping chamber. During the intake phase of the pump, it is the elasticity of the diaphragm which produces the return stroke generating, on the one hand, the intake and, on the other hand, returning the drive mechanism 7 to its starting position. As a result, suitable sizing of the diaphragm 1 is of key importance in order:
To have sufficient intake (be capable of creating enough of a reduced pressure) at the time of filling to combat any reduced pressure (pressure drop in a pipe, height of water column, valve with pressure threshold, etc.) and achieve sufficiently rapid filling of the pumping chamber, and to do so over the entire operating range thereof.
However, in order to avoid shockwaves in the lines, effects of vaporization of the liquid contained in the pumping chamber 1 as a result of a pressure drop beyond the vapour pressure of this liquid, or alternatively the effects of cavitation, the intake must not create too great a pressure drop.
Not to be too sensitive to the pressure in the upstream and downstream pipes, so as to maintain the precision of the incremental volumes pumped and therefore the precision of the flow rate, irrespective of the pressures upstream and downstream of the pumping device.
We are now going to look at the sizing of the pumping diaphragm in order to obtain adequate filling.
In what follows of the description, the behaviour of an annular diaphragm of flat profile surrounding a central core the thickness of which is chosen such that it deforms as little as possible, ideally not at all bearing in mind the stresses to which it is exposed, will be compared.
The feature of foremost interest to us is the pressure reduction that the diaphragm is capable of supplying as a function of the displacement of its central core.
Dimensioning the pumping diaphragm 1 first of all goes through the step of defining an operating range. In order to allow the diaphragm to pump right from the beginning of its stroke giving rise to a raised pressure, it is necessary for the diaphragm to be subjected to a preload, as will be seen later on.
In the example adopted here, the preload of the diaphragm corresponds to a displacement by 0.4 mm from its rest position, the operating range extending from 0.4 mm to 1.2 mm. This operating zone is delimited by two vertical dotted lines in the diagram of
It is evident from that figure that the annular pumping diaphragm 1 has to have a rigidity such that the absolute pressure in the pumping chamber in the range of operation of the diaphragm situated between the extreme displacement position and the extreme return position lies within the following range:
P
atm−(|ΔPvalve
where:
In order to address this problem, the challenge is to create a diaphragm which can work at the most constant pressure possible over the operating range. That would make it possible, firstly, to operate in the permissible operating zone (an essential condition) and secondly to soften the shockwaves in the upstream pipe 3 and avoid vaporization of the liquid or cavitation.
In order to achieve a diaphragm something like this a diaphragm geometry that had a frustoconical profile in the state of rest was studied, this therefore resulting in the rigid central core of the flat diaphragm moving in a parallel plane, the annular part of the diaphragm then being conical in the state of rest. The forces resulting from the displacement of the rigid central core parallel to its plane in such a frustoconical diaphragm can be broken down into tension-compression forces and to forces of bending of the flexible annular part.
A distinction is made between three types of behaviour as the central core gradually moves parallel to its plane:
Hence, a diaphragm of frustoconical shape has a pressure-displacement characteristic in the shape of a wave resulting from the buckling phenomenon.
A distinction can be drawn between two different types of behaviour according to the thickness of such a diaphragm:
A combination of these two extreme solutions, like the one illustrated in
The type of profile of pumping diaphragm 1 of
One way of reducing pressure sensitivity of the conical annular pumping diaphragm would be to reduce the operating range and to increase the preload, for example by switching from an operating range of 0.3 to 1.3 mm to an operating range of 0.7 to 1.2 mm. In such a case, it would be possible to reduce the rigidity of the diaphragm, the gradient of which would then typically be 1×104 Pa/0.2 mm and which would work over a narrower range, like that of
Nevertheless, a diaphragm such as this would have the following disadvantages:
In order to illustrate this sensitivity to pressure,
In each case, the diagrams illustrate the central core 1a of the diaphragm in two positions parallel to its plane with respect to its outer edge fixed to the pumping chamber.
The diaphragm is illustrated in a first extreme position under preload of the central core 1a, that corresponds to the extreme return position of the diaphragm, once under zero pressure and once under a pressure of −3×104 Pa.
The diaphragm is illustrated in its extreme displacement position corresponding to the end of the stroke used to expel liquid from the pumping chamber, once at zero pressure and once at 1.2×105 Pa.
It may be seen in
The various preferred dimensional parameters for the diaphragm in order to obtain the desired effects as far as the pressure-displacement characteristic is concerned, and as far as the reduction in pressure sensitivity is concerned are indicated in
The dimensional parameters of this diaphragm that contribute to obtaining the aforementioned characteristics are as follows, and need to fall within the following ranges:
for an elastic material the elastic modulus of which ranges between 0.1 MPa≦E≦100 MPa. It is also the parameters b and e that can influence the pressure-displacement curve.
Increasing ΔR/Rext leads to a reduction in the compression/relaxation of compression, a reduction in tension. This increase in ΔR/Rext also has the effect of reducing the pressure amplitude of the pressure-displacement curve (see
Increasing H/Rext has the effect of increasing the compression, relaxation of compression, of increasing the tension, of increasing the possible stroke of the diaphragm and of increasing the pressure amplitude of the pressure-displacement curve.
Increasing e/ΔR increases the bending effects and the rigidity and reduces the amplitude of the pressure-displacement curve (
The table below gives, by way of example, the dimensional and frequency/flow rate parameters of three pumping devices that form subjects of the present invention.
Advantageously, the diaphragm is made of silicone. It could also be made of polyurethane or of EPDM. The pumping chamber is advantageously made of polycarbonate and the diaphragm of
Number | Date | Country | Kind |
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1982/09 | Dec 2009 | CH | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/CH2010/000319 | 12/20/2010 | WO | 00 | 8/15/2012 |