U.S. patent application number 13/518376 was filed with the patent office on 2012-12-06 for diaphragm metering pump device for medical use.
Invention is credited to Jean-Denis Rochat.
Application Number | 20120308412 13/518376 |
Document ID | / |
Family ID | 43971530 |
Filed Date | 2012-12-06 |
United States Patent
Application |
20120308412 |
Kind Code |
A1 |
Rochat; Jean-Denis |
December 6, 2012 |
Diaphragm Metering Pump Device for Medical Use
Abstract
This pump comprises a chamber and an annular pumping diaphragm
secured to the said chamber and the inner edge of which is secured
to a central drive part. This diaphragm has a convex domed profile
so that its expulsion stroke results essentially in the
energy-generating flexing of the intake stroke. The rigidity of the
diaphragm is chosen so that the absolute pressure of the chamber
lies within the following range:
P.sub.atm-(|.DELTA.P.sub.valve.sub.--.sub.in|+|.DELTA.P.sub..DELTA.h.sub-
.--.sub.in|+|.DELTA.P.sub.pd|).gtoreq.P>P.sub.vap where:
P.sub.atm=atmospheric pressure, P.sub.vap=vapour pressure of the
pumped fluid, .DELTA.P.sub.valve.sub.--.sub.in=pressure difference
between the upstream and downstream side of the inlet valve for
opening it, .DELTA.P.sub..DELTA.h.sub.--.sub.in=pressure difference
in the upstream pipe between its distal end and the upstream side
of the inlet valve as a result of the weight of the column of
fluid, .DELTA.P.sub.pd=pressure drop in the upstream pipe for the
desired flow rate.
Inventors: |
Rochat; Jean-Denis;
(Genolier, CH) |
Family ID: |
43971530 |
Appl. No.: |
13/518376 |
Filed: |
December 20, 2010 |
PCT Filed: |
December 20, 2010 |
PCT NO: |
PCT/CH2010/000319 |
371 Date: |
August 15, 2012 |
Current U.S.
Class: |
417/395 |
Current CPC
Class: |
A61M 5/14224 20130101;
A61M 5/14586 20130101; F04B 43/0054 20130101 |
Class at
Publication: |
417/395 |
International
Class: |
F04B 43/06 20060101
F04B043/06 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 23, 2009 |
CH |
1982/09 |
Claims
1. 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, characterized in that
the said annular pumping diaphragm has, in the said extreme return
position, a convex annular profile domed towards the outside of the
said pumping chamber so that its expulsion stroke results
essentially in the energy-generating flexural deformation of the
intake stroke and in the annular compression/relaxation of
compression of the said convex annular profile upon each outward
stroke of the said diaphragm, the rigidity of the diaphragm being
chosen so 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.sub.atm-(|.DELTA.P.sub.valve.sub.--.sub.in|+|.DELTA.P.sub..DELTA.h.sub.-
--.sub.in|+|.DELTA.P.sub.pd|).gtoreq.P>P.sub.vap where:
P.sub.atm=atmospheric pressure P.sub.vap=vapour pressure of the
pumped fluid .DELTA.P.sub.valve.sub.--.sub.in=pressure difference
between the upstream and downstream side of the inlet valve for
opening it .DELTA.P.sub..DELTA.h.sub.--.sub.in=pressure difference
in the upstream pipe between its distal end and the upstream side
of the inlet valve as a result of the weight of the column of fluid
.DELTA.P.sub.pd=pressure drop in the upstream pipe for the desired
flow rate.
2. Pumping device according to claim 1, in which the said diaphragm
is made of silicone.
3. Device according to claim 1, in which the ratio between the
radial width .DELTA.R of the annular part of the pumping diaphragm
and the exterior radius thereof lies within the range: 0.1 .ltoreq.
.DELTA. R R ext .ltoreq. 0.9 ##EQU00002##
4. Device according to claim 1, in which the ratio between the
radial width .DELTA.R of the annular part of the annular pumping
diaphragm and the length of the stroke of the diaphragm between its
extreme return position and its extreme displacement position lies
within the range: 0.05 .ltoreq. .DELTA. R d max .ltoreq. 5
##EQU00003##
5. Device according to claim 1, in which the ratio between the
thickness e of the annular pumping diaphragm and the radial width
.DELTA.R of the annular part thereof lies within the range: 0.01
.ltoreq. e .DELTA. R .ltoreq. 1 ##EQU00004##
6. Device according to claim 1, in which the ratio between the
maximum distance between the chord subtended by the concave side of
the annular part of the diaphragm and the thickness e of this
diaphragm lies within the range: 0 < b e < 10 ##EQU00005##
for an elastic material the elastic modulus E of which ranges
between 0.1 MPa.ltoreq.E.ltoreq.100 MPa.
7. Device according to claim 1, in which said range of operation
lies between 0.7 and 1.2 mm, with a rigidity of the diaphragm
having a gradient of typically 1.10.sup.4 Pa/0.2 mm.
8. Device according to claim 1, in which the pumping chamber is
made of polycarbonate.
9. Device according to claim 1, in which the annular pumping
diaphragm is an element overmoulded on the pumping chamber.
Description
[0001] 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.
[0002] 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.
[0003] 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.
[0004] 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.
[0005] 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.
[0006] 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.
[0007] Meeting all of these conditions, some of which oppose
others, is therefore not straightforward.
[0008] It is an object of the present invention to provide a
solution which is able, at least in part, to meet the
aforementioned conditions.
[0009] To this end, the subject of the present invention is a
metering pump device for medical use according to Claim 1.
[0010] 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.
[0011] FIG. 1 is a schematic general arrangement of the metering
pump device;
[0012] FIG. 2 is a diagram illustrating a typical operating pumping
range using a flat pumping diaphragm;
[0013] FIG. 3 is a cross section through a pumping diaphragm
according to the invention intended to be connected to a pumping
chamber;
[0014] FIG. 4 is a pressure-displacement diagram for a pumping
device using the diaphragm of FIG. 3;
[0015] FIG. 5 is a comparative pressure-displacement diagram of a
pumping device using a flat diaphragm with the same dimensional
ratios as the diaphragm of FIG. 3;
[0016] FIG. 6 is a diagram showing the pressure sensitivity of the
diaphragm of FIG. 3;
[0017] FIG. 7 is a comparative pressure-sensitivity diagram for the
flat diaphragm of FIG. 5;
[0018] FIG. 8 is a diagram of the diaphragm of the pumping device
that forms the subject of the invention, showing the characteristic
dimensions the dimensional ratios of which will be discussed
further in the description.
[0019] The metering pump device that forms the subject of the
invention is illustrated very schematically in FIG. 1, given that
it is the elastically deformable pumping diaphragm 1, and the
geometry and structure thereof, which constitute the innovative
part of this invention.
[0020] 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.
[0021] 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.
[0022] 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:
[0023] 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.
[0024] 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.
[0025] 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.
[0026] We are now going to look at the sizing of the pumping
diaphragm in order to obtain adequate filling.
[0027] 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.
[0028] 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.
[0029] 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.
[0030] 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
FIG. 2. The pressure in the pumping chamber must not drop below the
vaporization pressure of water, represented by the lower line.
Finally, the operating range needs to lie at a pressure below
-2.times.10.sup.4 Pa, in order to counter the pressure of the
liquid on the upstream side of the inlet valve 4 (1.times.10.sup.4
Pa), the height of the water column to be taken in
(5.times.10.sup.3 Pa) and a minimum of 5.times.10.sup.3 Pa in order
to return the drive member 7 to its starting position. The working
zone of the pumping diaphragm 1 is therefore defined by the
rectangle bounded by the two vertical dotted lines and the two
horizontal lines. Nonetheless, in order to take tolerances into
consideration, a margin of 0.1 mm on the displacement of the
pumping diaphragm is provided, as illustrated by the two continuous
vertical lines. The possible operating zone then ranges between 0.3
and 1.3 mm, as illustrated in FIG. 2.
[0031] 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.sub.atm-(|.DELTA.P.sub.valve.sub.--.sub.in|+|.DELTA.P.sub..DELTA.h.sub-
.--.sub.in|+|.DELTA.P.sub.pd|).gtoreq.P>P.sub.vap
where: [0032] P.sub.atm=atmospheric pressure [0033]
P.sub.vap=vapour pressure of the pumped fluid [0034]
.DELTA.P.sub.valve.sub.--.sub.in=pressure difference between the
upstream and downstream side of the inlet valve for opening it
[0035] .DELTA.P.sub..DELTA.h.sub.--.sub.in=pressure difference in
the upstream pipe between its distal end and the upstream side of
the inlet valve as a result of the weight of the column of fluid
[0036] .DELTA.P.sub.pd=pressure drop in the upstream pipe for the
desired flow rate.
[0037] FIG. 2 again depicts the pressure-displacement curve for the
aforementioned flat diaphragm. It may be noted that a situation is
reached where the reduced pressure generated by the moving
diaphragm x>0.7 mm is far too great, which could give rise to
shockwaves (pressure waves in the upstream pipe 3), to boiling
phenomena resulting from a drop in pressure and/or to cavitation.
In other words, the gradient which is about -1.times.10.sup.4
Pa/0.1 mm is too steep. Conversely, if attempts are made to reduce
the gradient as far as possible, there is a risk of being at a
pressure equal to -2.times.10.sup.4 Pa at the prestress position of
the diaphragm corresponding to a displacement of 0.3 mm and of not
being able to complete the intake, or, put another way, of having
an intake smaller than the pumping volume of the pump.
[0038] 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.
[0039] 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.
[0040] A distinction is made between three types of behaviour as
the central core gradually moves parallel to its plane: [0041] The
diaphragm works chiefly in compression, bending being of secondary
importance. [0042] Compression decreases with the displacement of
the core as far as a threshold where the diaphragm buckles and
compression forces are relaxed. Bending forces increase. [0043] The
compression forces are completely relaxed and the diaphragm works
in tension. The bending forces continue to increase with
displacement.
[0044] Hence, a diaphragm of frustoconical shape has a
pressure-displacement characteristic in the shape of a wave
resulting from the buckling phenomenon.
[0045] A distinction can be drawn between two different types of
behaviour according to the thickness of such a diaphragm: [0046]
When the thickness is very small and the cone angle is pronounced,
the diaphragm undergoes a great deal of buckling, and behaves like
a bi-stable diaphragm, the pressure-displacement characteristic of
which forms a very pronounced S shape. In this case, it is the
tension-compression forces which dominate. [0047] If the thickness
is great and the gradient small, the buckling phenomenon appears
little if at all; this then is a stable diaphragm, the
pressure-displacement characteristic of which does not form an S
shape. It is the bending forces that dominate.
[0048] A combination of these two extreme solutions, like the one
illustrated in FIG. 3, gives an interesting curve. FIG. 4
illustrates the pressure-displacement curve of an annular diaphragm
of the kind in FIG. 3 that forms the subject of the invention and
the geometry of which is essentially characterized by a convex
annular profile domed towards the outside of the pumping chamber.
In this embodiment, the outer edge of the diaphragm 1 is secured to
an annular connecting element 1b which has an annular groove 1c
intended to allow it to be attached to the wall of the pumping
chamber 2.
[0049] The type of profile of pumping diaphragm 1 of FIG. 3 makes
it possible to alter the distance between the plane of the central
core 1a of this diaphragm 1 and the plane that passes through the
outer edge of the annular diaphragm 1, where it is connected to the
pumping chamber by the annular connecting element 1b. The diameter
of the central core 1a can also be varied. Thus, by varying various
geometric parameters of the pumping diaphragm 1, it is possible to
modify the amplitude of the pressure-displacement curve of FIG. 4.
The following effects are noted according to the characteristics of
the diaphragm 1 of FIG. 3: [0050] The more acute the cone angle,
the more the tension-compression forces dominate and the more the
pressure-displacement characteristic of the diaphragm adopts a
pronounced S shape. [0051] The thicker the annular diaphragm 1, the
more the bending forces dominate: [0052] the less the
pressure-displacement characteristic adopts a pronounced S shape
[0053] the steeper the gradient of the pressure-displacement
characteristic [0054] the narrower the operating range of the
diaphragm [0055] The more domed the shape of the annular diaphragm
1, the more the bending forces dominate and the lesser the extent
to which the pressure-displacement characteristic adopts a
pronounced S shape.
[0056] 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.times.10.sup.4 Pa/0.2 mm and which would work over a narrower
range, like that of FIG. 5.
[0057] Nevertheless, a diaphragm such as this would have the
following disadvantages: [0058] The preload of the diaphragm is
increased, which means that the forces within the diaphragm are
greater. [0059] The flow rate of the pumping device is reduced in
the same ratio as the operating range. [0060] A device such as this
is far more sensitive to pressure because the thickness of the
diaphragm has been reduced in order to reduce the gradient of the
pressure-displacement curve which means that the pressure
sensitivity of such a diaphragm is greatly increased, this
significantly reducing the precision of the flow rate.
[0061] In order to illustrate this sensitivity to pressure, FIGS. 6
and 7 indicate the pressure sensitivity of the diaphragm of FIG. 3,
as compared with a flat annular diaphragm with the same ratios of
inside/outside diameters:
[0062] 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.
[0063] 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.times.10.sup.4 Pa.
[0064] 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.times.10.sup.5 Pa.
[0065] It may be seen in FIG. 6 that the diaphragm according to the
present invention is not very sensitive to pressure. Specifically,
very little difference can be observed between the curve in
continuous line and the curve in dotted line in which it is
subjected to a reduced pressure of -3.times.10.sup.4 Pa or even
between the curves in chain line and the curve in dashes and
crosses in which it is subjected to a pressure of
1.2.times.10.sup.5 Pa. By contrast, in FIG. 7, a large effect that
pressure has on the shape of the diaphragm can be seen under the
same measurement conditions.
[0066] 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
FIG. 8 which is a cross section through half of the diaphragm 1
from its centre to its periphery.
[0067] The dimensional parameters of this diaphragm that contribute
to obtaining the aforementioned characteristics are as follows, and
need to fall within the following ranges:
H > 0 ##EQU00001## 0.1 .ltoreq. .DELTA. R R ext .ltoreq. 0.9
##EQU00001.2## 0.0 .5 .ltoreq. .DELTA. R d max .ltoreq. 5
##EQU00001.3## 0.01 .ltoreq. e .DELTA. R .ltoreq. 1 ##EQU00001.4##
0 < b e < 10 ##EQU00001.5##
for an elastic material the elastic modulus of which ranges between
0.1 MPa.ltoreq.E.ltoreq.100 MPa. It is also the parameters b and e
that can influence the pressure-displacement curve.
[0068] Increasing .DELTA.R/R.sub.ext leads to a reduction in the
compression/relaxation of compression, a reduction in tension. This
increase in .DELTA.R/R.sub.ext also has the effect of reducing the
pressure amplitude of the pressure-displacement curve (see FIG. 4),
making it flatter.
[0069] Increasing H/R.sub.ext 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.
[0070] Increasing e/.DELTA.R increases the bending effects and the
rigidity and reduces the amplitude of the pressure-displacement
curve (FIG. 4), flattening it.
[0071] 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.
TABLE-US-00001 Volume [.mu.l] 75 10 1 E.sub.diaphragm [MPa] 3.5 3.5
3.5 R.sub.ext [mm] 6.0 2.5 1.0 R.sub.central [mm] 3.5 1.5 0.6 H
[mm] 0.5 0.4 0.3 Stroke [mm] 1 0.8 0.5 Freq.sub.min [Hz] 0.004
0.003 0.003 Freq.sub.max [Hz] 4 15 30 Flow rate.sub.min [ml/h] 1
0.1 0.01 Flow rate.sub.max [ml/h] 1000 500 100
[0072] 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 FIG. 3 is
welded.
* * * * *