U.S. patent application number 11/801667 was filed with the patent office on 2008-02-07 for valve for controlling flow of a fluid.
This patent application is currently assigned to Beta Micropump Partners L.L.C.. Invention is credited to John Krumme.
Application Number | 20080029393 11/801667 |
Document ID | / |
Family ID | 34217490 |
Filed Date | 2008-02-07 |
United States Patent
Application |
20080029393 |
Kind Code |
A1 |
Krumme; John |
February 7, 2008 |
Valve for controlling flow of a fluid
Abstract
A valve for controlling flow of a primary fluid in a primary
flow channel comprises a valve fluid channel, and a membrane of a
porous dielectric material located in the channel so as to divide
the channel into an inlet part and an outlet part and so that valve
fluid flowing between the inlet and outlet parts flows through the
said membrane. First and second electrodes are located for
electrical communication with valve fluid in the inlet and outlet
parts respectively of the valve fluid channel for application of an
electric potential across the membrane in order to promote
electro-osmotic flow of valve fluid through the membrane. A valve
member can be displaced between open and closed positions as a
result of valve fluid moving in the valve fluid channel through the
membrane, into or out of the outlet part of the valve fluid
channel, in which the valve member causes a reduction in the
capacity for flow of the primary fluid in the primary flow channel
when it is in the closed position compared with when it is in the
open position.
Inventors: |
Krumme; John; (Tahoe City,
CA) |
Correspondence
Address: |
MADSON & AUSTIN
15 WEST SOUTH TEMPLE
SUITE 900
SALT LAKE CITY
UT
84101
US
|
Assignee: |
Beta Micropump Partners
L.L.C.
|
Family ID: |
34217490 |
Appl. No.: |
11/801667 |
Filed: |
May 10, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10651835 |
Aug 29, 2003 |
7217351 |
|
|
11801667 |
May 10, 2007 |
|
|
|
Current U.S.
Class: |
204/600 ;
251/129.01 |
Current CPC
Class: |
F16K 7/10 20130101; F04B
19/006 20130101; G05D 7/0635 20130101; A61K 9/0024 20130101; F16K
31/1266 20130101; B01D 61/425 20130101 |
Class at
Publication: |
204/600 ;
251/129.01 |
International
Class: |
G01N 27/00 20060101
G01N027/00; F16K 31/02 20060101 F16K031/02 |
Claims
1. A valve for controlling flow of a primary fluid in a primary
flow channel, which comprises: a. a valve fluid channel, b. a
membrane of a porous dielectric material located in the channel so
as to divide the channel into an inlet part and an outlet part and
so that valve fluid flowing between the inlet and outlet parts
flows through the said membrane, c. first and second electrodes
located for electrical communication with valve fluid in the inlet
and outlet parts respectively of the valve fluid channel for
application of an electric potential across the membrane in order
to promote electro-osmotic flow of valve fluid through the
membrane, d. a valve member which can be displaced between open and
closed positions as a result of valve fluid moving in the valve
fluid channel through the membrane, into or out of the outlet part
of the valve fluid channel, in which the valve member causes a
reduction in the capacity for flow of the primary fluid in the
primary flow channel when it is in the closed position compared
with when it is in the open position.
2. A valve as claimed in claim 1, in which the outlet part of the
valve fluid channel is closed so that fluid flowing into or out of
the outlet part flows through the membrane.
3. A valve as claimed in claim 2, in which at least part of the
wall of the outlet part of the valve fluid channel is defined by an
expandable diaphragm.
4. A valve as claimed in claim 3, in which the diaphragm is
provided by a resiliently deformable material.
5. A valve as claimed in claim 3, in which the diaphragm is
provided by expandable bellows.
6. A valve as claimed in claim 3, in which the valve fluid channel
has a side wall and an end wall, and in which the diaphragm is
located on the side wall so that the channel can expand
transversely in response to an increase in fluid pressure in the
outlet part of the valve fluid channel.
7. A valve as claimed in claim 3, in which the outlet part of the
valve fluid channel is located at least partially within the
primary flow channel so that an increase in fluid pressure in the
outlet part of the valve fluid channel causes the diaphragm to
expand towards the wall of the primary flow channel to close the
primary flow channel at least partially against flow of the primary
fluid.
8. A valve as claimed in claim 7, in which the diaphragm expands
transversely relative to the valve fluid channel, towards the wall
of the primary flow channel.
9. A valve as claimed in claim 3, in which the valve fluid channel
has a side wall and an end wall, and in which the diaphragm is
located at the end wall so that the channel can expand
longitudinally in response to an increase in fluid pressure in the
outlet part of the valve fluid channel.
10. A valve as claimed in claim 9, in which the primary flow
channel includes an orifice through which the primary fluid can
flow, and in which the end wall of the valve fluid channel is
located adjacent to the orifice so that, an increase in fluid
pressure in the outlet part of the valve fluid channel causes the
diaphragm to expand towards the orifice to close it at least
partially against flow of the primary fluid.
11. A valve as claimed in claim 3, in which the valve member
comprises a mandrel mounted on the diaphragm so that it is
displaced when the diaphragm expands in response to an increase in
fluid pressure in the outlet part of the valve fluid channel.
12. A valve as claimed in claim 3, in which primary flow channel
comprises a tube which can be compressed transversely so as to
reduce the cross-sectional area thereof, the said tube being
located relative to the valve fluid channel so that it is
compressed by the action against it of the diaphragm when it
expands in response to an increase in fluid pressure in the outlet
part of the valve fluid channel.
13. A valve as claimed in claim 1, in which the valve member
comprises a compressible tube which forms part of the primary flow
channel, the compressible tube being located within a chamber which
is in fluid communication with the outlet part of the valve fluid
channel so that an increase in fluid pressure in the said chamber
as a result of flow of valve fluid into the outlet part of the
valve fluid channel can cause compression of the compressible tube,
to reduce the flow of the primary fluid through the compressible
tube.
14. A valve as claimed in claim 1, in which the inlet part of the
valve fluid channel is closed so that fluid flowing into or out of
the inlet part flows through the membrane.
15. A valve as claimed in claim 14, which includes a quantity of a
valve fluid located within the valve fluid channel and a primary
fluid in the primary flow channel, in which the compositions of the
valve fluid and the primary fluid are different from one
another.
16. A valve as claimed in claim 1, in which the inlet part of the
valve fluid channel is in communication with the primary flow
channel.
17. A valve as claimed in claim 1, which includes a valve member
housing in which the valve member can move between the said open
and closed positions.
18. A valve as claimed in claim 17, in which the valve member
housing has a housing inlet and a housing outlet which communicate
with the primary flow channel so that primary fluid flowing along
the primary flow channel flows through the valve member housing,
through the said housing inlet and housing outlet.
19. A valve as claimed in claim 18, in which the direction of flow
of primary fluid through the valve member housing is generally
transverse to the direction in which the valve member moves between
its open and closed positions.
20. A valve as claimed in claim 17, in which the valve member is a
close fit within the valve member housing so that a seal is formed
between facing surfaces of the valve member and the valve member
housing to minimise mixing of the primary fluid and the valve
fluid.
21. A valve as claimed in claim 20, in which the valve member
provides a flow path which can be aligned with the housing inlet
and the housing outlet when the valve member is in the open
position for the primary fluid to flow through the housing.
22. A valve as claimed in claim 21, in which the flow path is
defined by a region of the valve member with a reduced
cross-section.
23. A valve as claimed in claim 21, in which the flow path is
defined by an aperture extending through the valve member.
24. A valve as claimed in claim 17, in which the valve member
housing has a first end towards which the valve member moves when
moving towards its open position from its closed position and an
opposite second end towards which the valve member moves when
moving towards its closed position from its open position, and in
which the valve member housing has a first opening at or towards
the first end thereof which communicates with the inlet part of the
valve fluid channel and a second opening at or towards the second
end thereof which communicates with the outlet part of the valve
fluid channel.
25. A valve as claimed in claim 1, which is incorporated as a
driver valve in a pump for controlling the flow of a primary
fluid.
26. A pump for controlling flow of a primary fluid in a primary
flow channel, which comprises: a. a driver valve comprising: i. a
valve fluid channel, ii. a membrane of a porous dielectric material
located in the channel so as to divide the channel into an inlet
part and an outlet part and so that valve fluid flowing between the
inlet and outlet parts flows through the said membrane, iii. first
and second electrodes located for electrical communication with
valve fluid in the inlet and outlet parts respectively of the valve
fluid channel for application of an electric potential across the
membrane in order to promote electro-osmotic flow of valve fluid
through the membrane, iv. a valve member which can be displaced
between open and closed positions as a result of valve fluid moving
in the valve fluid channel through the membrane, into or out of the
outlet part of the valve fluid channel, in which the valve member
causes a reduction in the volume of the primary flow channel when
it is in the closed position compared with when it is in the open
position, b. an inlet valve located upstream of the driver valve,
for controlling flow of primary fluid into the primary flow channel
where it is acted on by the driver valve, and c. an outlet valve
located downstream of the driver valve, for controlling release of
primary fluid from the primary flow channel where it is acted on by
the driver valve.
27. A pump as claimed in claim 26, which includes a latching valve
to control flow of the valve fluid in the valve fluid channel.
28. A pump as claimed in claim 27, in which the latching valve is a
valve as claimed in claim 19.
29. A pump as claimed in claim 26, in which at least one of the
inlet valve and the outlet valve comprises a valve as claimed in
claim 1.
Description
CROSS-REFERENCED RELATED APPLICATIONS
[0001] This application is a continuation of prior application Ser.
No. 10/651,835, filed Aug. 29, 2003. This invention relates to a
valve for controlling flow of a fluid in a flow channel, and to a
pump for controlling flow of a fluid in a flow channel.
BACKGROUND OF THE INVENTION
[0002] The flow of fluids through conduits can be controlled using
components such as pumps and valves. Pumps and valves can operate
to control parameters such as flow rate; adjustment of relative
flow rates of constituents in a mixture can be used to vary the
composition of the mixture.
[0003] Accurate control of flow of a fluid can be important in many
medical applications, for example in drug delivery and in the
modulation of body fluid drainage. Devices in which flow control is
important include pumps for dispensing drugs such as insulin and
opiates, and hydrocephalus shunts for drainage of spinal
fluids.
[0004] Accurate control over the flow of drugs and fluids in
medical applications can help to minimise complications in the
patient treatment, especially if controlled quantities of drugs can
be supplied locally to an affected site. Accurate control can help
to optimise efficacy of an administered drug. The use of controlled
quantities can also help to minimise wastage of drugs, and
therefore to minimise treatment costs. An implanted device for
controlling flow of drugs can help to ensure compliance with
prescribed drug administration regime by eliminating patient
dependence on operation of the device.
[0005] Accurate and localised control of a drug can be facilitated
by means of implanted control devices. U.S. Pat. No. 6,287,295
relates to an implantable device which relies on a semipermeable
membrane to control the rate of drug delivery. However, once
implanted, the rate of flow of drug through the membrane cannot
readily be adjusted.
[0006] Electro-osmotic flow controllers apply a potential
difference to liquid on opposite sides of a semi-permeable membrane
made of a dielectric material. Provided that the liquid is able to
yield a high zeta potential with respect to the porous dielectric
material of the membrane, the application of the potential
difference leads to transmission of charged species, possibly
together with solvent (for example which solvates the charged
species or as bulk solvent by viscous drag), through the membrane.
This technology can be used to control the rate at which a liquid
is supplied, for example under pressure which is generated by means
of a pump. The technology, including amongst other things details
of the materials which can be used for the membrane and as the
liquid which is transmitted across the membrane, is discussed in
detail in US-A-2002/189947. Subject matter disclosed in that
document is incorporated in the specification of the present
application by this reference.
BRIEF SUMMARY OF THE INVENTION
[0007] The present invention provides a valve for controlling flow
of a primary fluid in a primary flow channel, including a valve
member which can be displaced between open and closed positions as
a result of electro-osmotic flow of valve fluid, in which the valve
member causes flow of the primary fluid in the primary flow channel
to be interrupted when it is in the closed position, and allows
flow of the primary fluid in the primary flow channel when it is in
the open position.
[0008] Accordingly, in one aspect, the invention provides a valve
for controlling flow of a primary fluid in a primary flow channel,
which comprises:
[0009] a. a valve fluid channel,
[0010] b. a membrane of a porous dielectric material located in the
channel so as to divide the channel into an inlet part and an
outlet part and so that valve fluid flowing between the inlet and
outlet parts flows through the said membrane,
[0011] c. first and second electrodes located for electrical
communication with valve fluid in the inlet and outlet parts
respectively of the valve fluid channel for application of an
electric potential across the membrane in order to promote
electro-osmotic flow of valve fluid through the membrane,
[0012] d. a valve member which can be displaced between open and
closed positions as a result of valve fluid moving in the valve
fluid channel through the membrane, into or out of the outlet part
of the valve fluid channel, in which the valve member causes a
reduction in the capacity for flow of the primary fluid in the
primary flow channel when it is in the closed position compared
with when it is in the open position.
[0013] The valve of the present invention has the advantage that it
can be controlled by applying or changing the potential difference
across the membrane, allowing control of the rate or direction of
flow (or both) of fluid through the membrane. This can be a
particular advantage when access to the valve is restricted when it
is in use. In particular, this can be the case when the valve has
been implanted in a human or animal body. However, it is also
relevant when the valve is inaccessible in some other way, for
example when the valve is located within an enclosure (for example
a casing for fluid supply apparatus) or at a location which is
remote from an operator when wireless or wired communication
signals (for example telecommunications signals) can be used to
cause a change in the applied potential difference.
[0014] The valve of the invention relies on electro-osmotic flow of
the valve fluid through the membrane of porous dielectric material.
This effect arises when a liquid is in contact with a dielectric
solid and the natural electrochemistry of the interaction produces
a thin layer of net charge density in the liquid in the region of
the interface. An applied electric field which includes a component
perpendicular to the interface causes motion of the net charge.
Viscous action imparts motion to the adjacent liquid which remains
neutral. Accordingly, in the valve fluid channel of the valve of
the invention, a potential difference applied across the membrane
by means of the first and second electrodes produces
electro-osmotic flow of liquid through the membrane.
[0015] Electro-osmotic flow may be generated using a wide variety
of fluids and dielectric materials. Indeed, it is an advantage of
the present invention that the valve fluid can be isolated from the
primary fluid so that an optimum fluid can be selected for
operating the valve without reference to the particular
requirements or nature of the primary fluid. The valve fluid should
provide conditions that yield a high zeta potential with respect to
the porous dielectric material. The fluid might be a pure fluid or
a mixture of pure fluids. The fluid might have added to it a
conducting species, especially a material which dissolves in the
fluid to form ions. Preferably, the or each pure fluid should have
a high dielectric constant (for example, between about 5 and 100
relative units), low dynamic viscosity (for example, between about
0.1 and 2 centipoise) and low conductivity (for example, between
about 10.sup.-4 and 10.sup.-14 mho.multidot.m.sup.-1).
[0016] The valve fluid can include at least one additive to control
the pH of the fluid. The valve fluid can include at least one
additive to control the ionic strength of the fluid. Additives
should preferably dissolve completely in the fluid. The kind and
concentration of additives should preferably be such as to enhance
or to optimise the zeta potential under the conditions imposed by
the size of the pores in the porous dielectric medium.
[0017] The degree of ionization of the surface sites depends on the
pH of the fluid. In most cases there is a pH at which the surface
is net neutral and hence the zeta potential is zero. The zeta
potential reaches a maximum value for pH values significantly above
(for acidic surface sites) or pH values significantly below (for
basic surface sites) the pH value at which the surface is net
neutral. Ionisable surface sites can be added to a material by
chemical reaction or grafting, or induced by creation of reactive
surface chemistry or creation of defects via plasma or radiation
treatment.
[0018] Examples of fluids which can be used in the valve fluid
include water, cyclic carbonates, methanol, ethanol, 1-propanol,
2-propanol, 1-butanol, 1-pentanol, 1-hexanol, 1-heptanol, benzyl
alcohol, nitromethane, nitrobenzene, butanone, dimethoxymethane,
dimethylacetamide, dioxane, p-dioxane, acetonitrile, formamide,
tetrahydrofuran, dimethyl formamide, acetone, acetic acid,
triethylamine, dichloromethane, ethylene glycol,
dimethylsulphoxide, ammonium acetate.
[0019] The valve fluid can include additives which can affect the
zeta potential. Ionic species can have the opposite charge sign to
the zeta potential. Ionic species can have the same charge sign as
the zeta potential. Preferably, ionic species which are included in
the valve fluid are monovalent. Species which ionise fully can be
used to adjust the ionic strength of the fluid. Species which
ionise partially can be used to adjust the pH of the fluid.
Examples of useful ionic and buffering additives include
alkali-halide salts, mineral acids and bases, organic acids and
bases, phosphates, borates, acetates, citrates, malates, formates,
carbonates, chlorates, nitrates, sulphates and sulphites, nitrates
and nitrites, ammonium-, methylammonium-, ethylammonium-,
propylammonium-salts, BIS, MES, TRIS, TES, HEPES, and TEA.
[0020] Preferably, the materials of the valve fluid and the porous
dielectric material are such that the zeta potential is at least
about 1 mV, especially at least about 30 mV. Generally, the zeta
potential will be not more than about 150 mV, for example not more
than about 120 mV. The zeta potential may be either positive or
negative in sign. Factors affecting the sign and magnitude of the
zeta potential include the dielectric constant of the fluid, the pH
of the fluid, the ionic strength of the fluid, and the type of ions
in the fluid.
[0021] The surface of the porous dielectric material will generally
be required to exhibits acidic or basic sites that become ionised
in the presence of the valve fluid. These ionisable surface sites
may be native to the material or may be the result of adsorption of
some species onto the surface material. Examples of materials which
are inherently capable of creating ionised sites include silica
(which exhibits acidic surface sites), alumina (amphoteric) which
can exhibit basic or acidic surface sites, polyamides such as a
Nylon (which exhibits both acidic (carboxyl) and basic (amine)
surface sites--zwitterionic). The sign of the zeta potential is the
same as the sign of the net surface charge.
[0022] A membrane which is not capable inherently of creating
ionised sites (for example a polyolefin, such as polyethylene or
polypropylene or mixtures thereof) can be modified by means of
additives such as ionic surfactants. When such a membrane is
exposed to an aqueous solution containing certain ionic surfactants
(for example sodium dodecyl sulphate), the hydrophobic tail of the
surfactant adsorbs to the polymer, and the charged end of the
surfactant then appears as a charge site on the surface.
[0023] The dielectric material of the membrane is selected for
properties of high zeta potential, the sign of the zeta potential,
insolubility and stability in the valve fluid, low electrical
conductivity, and sufficient mechanical strength. Examples of
dielectric materials which can be used in the membrane include
ceramic oxides, glasses, ceramic nitrides, certain polymers,
carbides and silicides.
[0024] Examples of suitable oxide materials include silica,
alumina, titania, zirconia, cerium oxide, lanthanum oxide, yttrium
oxide, hafnium oxide, magnesium oxide, and tantalum oxide. These
oxides may be amorphous or glassy or crystalline and may be
combined in mixtures having other minor oxide components.
[0025] Examples of suitable nitride materials include silicon
nitride, boron nitride, and aluminium nitride.
[0026] Examples of suitable polymers include sulphonated
fluoropolymers (such as that sold under the trade mark Nafion),
polysulphones, polyethersulphones, polycarbonates,
polyacrylonitriles, polyvinylidene fluorides, polyamides (Nylon),
silicone elastomers and polymethacrylates.
[0027] Certain semiconductors might be used in the membrane, such
as carbides (for example titanium carbide) and suicides (for
example germanium silicide).
[0028] The geometry of the pores in the membrane will affect the
performance of the valve, including the length and transverse
dimension, and the tortuosity. Details of the formation of suitably
porous membranes and design parameters are known.
[0029] Preferably, the valve fluid channel comprises a tubular
member in which the membrane is located to divide the tubular
member into two parts which are spaced apart along the length of
the tubular member. The tubular member will often have a generally
constant cross-section along at least a substantial part of its
length, especially for ease of manufacture. Frequently, the tubular
member will have a rounded shape (especially a circular shape) when
viewed in cross-section along the axis of the member. However,
other shapes are envisaged, such as square or rectangular.
[0030] The tubular member of the valve fluid channel should have
sufficient mechanical strength to withstand the pressures which are
generated within it. The material should be compatible with and
impermeable to the fluids with which it will come into contact when
in use.
[0031] The membrane can be fabricated as a separate part and then
mounted in a tubular member or in a sheet. The membrane can be
fabricated in situ in a tubular member or sheet.
[0032] Other details of the materials, construction, operation of
devices which exhibit electro-osmotic flow properties are known,
for example as disclosed in US-A-2002/189947 and documents referred
to therein.
[0033] The valve fluid channel can be defined by the membrane of
the porous dielectric material, with inlet and outlet parts on
respective sides thereof which are defined by expandable inlet and
outlet diaphragms which are bonded to the membrane on opposite
sides thereof. The membrane can be provided in a sheet in which the
porous dielectric properties which are required for the
electro-osmotic effect to be exhibited are provided in a localised
region. The inlet and outlet diaphragms can then be bonded to the
sheet at locations outside the said localised region. A valve in
which the valve fluid channel is defined by a membrane with inner
and outer diaphragms in this way has the advantage that the valve
has a lower profile by virtue of smaller thickness, compared with a
valve in which the valve fluid channel is provided by a tubular
member.
[0034] A further advantage of the valve of the present invention is
that the primary fluid whose flow is controlled by the valve need
not have the characteristics which are necessary for
electro-osmotic flow effects to be demonstrated by it. Accordingly,
the valve can be used to control the flow of fluids which are not
capable in normal operating conditions of demonstrating a zeta
potential with respect to the dielectric material of the membrane.
The valve can also be used to control the flow of fluids which are
too viscous to be able to flow through a membrane of a suitable
dielectric material. Instead of relying on the primary fluid to
demonstrate electro-osmotic flow effects, these effects can be
provided by a fluid which is different from the primary fluid,
referred to herein as the valve fluid. Electro-osmotic flow of the
valve fluid causes displacement of the valve member which can then
act mechanically to control the capacity of the primary fluid
channel, for example to affect the rate of flow of the primary
fluid along that channel or to affect the volume of the channel for
the primary fluid.
[0035] The outlet part of the valve fluid channel will generally be
a closed chamber so that fluid flowing into or out of the outlet
part flows through the membrane. Accordingly, flow of fluid into or
out of the outlet part of the valve fluid channel can cause the
volume of the outlet part of the valve fluid channel to change, for
example by deformation (such as inward or outward deformation) of
at least a part of the wall of the outlet part. For example, the
deformation can be outward deformation when the valve member acts
against a primary flow channel which is located externally of the
valve fluid channel. The deformation can be inward deformation when
the primary flow channel is provided a compressible tube which
extends through the outlet part of the valve fluid channel: the
compressible tube then defines an internal wall of the outlet part
of the valve fluid channel.
[0036] Preferably, at least part of an external wall of the outlet
part of the valve fluid channel is defined by a diaphragm which can
expand. The construction of the diaphragm can be such that it
expands in the manner of a balloon when the material of the
diaphragm is resiliently deformable.
[0037] A diaphragm which defines part (or all) of the wall of the
outlet part of the valve fluid channel can be provided by a
resiliently deformable material. For example, an elastomeric
material can be used. Suitable elastomeric materials will be
selected according to the fluids with which the valve will come
into contact when in use. Examples might include certain silicones,
ethylene-propylene copolymers, and urethanes. Characteristics of a
deformable material for the diaphragm, such as its thickness and
other factors which affect its deformability, will be selected
according to the intended application for the valve, including the
pressures to which it will be exposed. The characteristics of
certain deformable polymeric materials can be optimised by
crosslinking.
[0038] A diaphragm which is formed from a resiliently deformable
material can be provided on a tubular valve fluid channel which is
relatively non-deformable (such that its dimensions remain
substantially unaltered during normal operation of the valve). The
diaphragm can be sealed to the surface of the tubular fluid
channel, with openings in the tubular fluid channel for the valve
fluid to flow into the space defined by the diaphragm. For example,
one or more openings can be provided in the longitudinal side wall
of the tubular fluid channel, or one or more openings can be
provided in the end wall of the tubular fluid channel.
[0039] The diaphragm can be provided by expandable bellows.
Expandable bellows are able to accommodate a change in the volume
of the outlet part of the valve fluid channel by a change in their
shape, with or without significant deformation of the material of
the diaphragm. For example, the diaphragm could have a compact
configuration in which it is folded when the volume of the valve
fluid channel is relatively small, and an extended configuration in
which the folds are opened out when the volume of the valve fluid
channel is greater.
[0040] Preferably, the valve fluid channel includes a tubular
member which has a side wall and an end wall, and the diaphragm is
located on the side wall so that the channel can expand
transversely in response to an increase in fluid pressure in the
outlet part of the valve fluid channel. A diaphragm which is
provided on the side wall of the valve fluid channel will be in
communication with the interior of the said channel, preferably by
means of one or more openings in the wall of the channel,
especially in the side wall thereof. The diaphragm should be sealed
to the valve fluid channel to prevent loss of valve fluid.
[0041] The outlet part of the valve fluid channel can be located at
least partially within the primary flow channel, especially when it
includes a tubular member, so that an increase in fluid pressure in
the outlet part of the valve fluid channel causes the outlet part
diaphragm to expand (for example by deformation of a resiliently
deformable material, or by expansion of bellows, or by a
combination of the two) towards the wall of the primary flow
channel to control the capacity of the primary fluid channel.
Preferably, the diaphragm expands transversely relative to the
valve fluid channel, towards the wall of the primary flow channel.
This arrangement finds particular application when the diaphragm is
located on the side wall of the valve fluid channel and expands
transversely in response to an increase in fluid pressure in the
outlet part of the said channel. The diaphragm can then close at
least partially the space between the internal wall of the primary
flow channel and the valve fluid channel to restrict or to stop
flow of the primary fluid through that space.
[0042] When the valve fluid channel includes a tubular member which
has a side wall and an end wall, the diaphragm can be located at
the end wall so that the channel can expand longitudinally in
response to an increase in fluid pressure in the outlet part of the
valve fluid channel. This arrangement finds application when the
primary flow channel includes an orifice through which the primary
fluid can flow, and the end wall of the valve fluid channel is
located adjacent to the orifice. An increase in fluid pressure in
the outlet part of the valve fluid channel can cause the diaphragm
to expand (for example by deformation of a resiliently deformable
material, or by expansion of bellows, or by a combination of the
two) towards the orifice to close it at least partially against
flow of the primary fluid. This arrangement is suitable for use of
the construction of valve discussed above in which inlet and outlet
diaphragms are fastened to a sheet of which a localised region
provides the membrane of porous dielectric material.
[0043] A diaphragm can be arranged as a balloon which is fastened
to a surface of the valve fluid channel, especially when the valve
fluid channel includes a tubular member. For example, the diaphragm
can be provided as an envelope on and around the end of the tubular
member of a valve fluid channel, fastened to the external surface
of the member.
[0044] The valve member can include a mandrel which is mounted on
the diaphragm so that it is displaced when the diaphragm expands in
response to an increase in fluid pressure in the outlet part of the
valve fluid channel. This can provide for more accurate sealing of
an orifice to close it against fluid flow for example by suitable
matching of the shape of the end of the mandrel with the shape of
the orifice. A mandrel will commonly be made from a relatively
rigid material so that it retains its shape, although it can have
an outer surface of a deformable material to provide compliance
with the shape of the primary flow channel, especially when the
mandrel is intended to fit into an orifice or other profiled
recess.
[0045] It is an advantage of the use of an electro-osmotic flow
device in the present invention that precise control over the rate
of flow of primary fluid is possible. The device can be configured
so that the pressure that is generated in the outlet part of the
valve fluid channel increases approximately linearly with the
potential difference across the membrane. A device can be
configured so that the pressure in the outlet part is about 400 kPa
when the potential difference across the membrane is about 18
volts.
[0046] The primary flow channel can comprise a tube which can be
compressed transversely so as to reduce the cross-sectional area
thereof and its capacity. Such a reduction in area can result in a
reduction in the rate of flow of fluid through the primary flow
channel. It can also be used to cause a reduction in the volume of
the primary flow channel that is available for the primary fluid,
especially by compressing it over a significant length. The length
over which the tube is compressed can be greater than is necessary
simply to close the tube to flow of fluid. This can be useful when
the valve is used as a part of a pump as discussed in more detail
below.
[0047] A compressible tube can be compressed as a result of being
located relative to the valve fluid channel so that it is
compressed by the action against it of the diaphragm when it
expands in response to an increase in fluid pressure in the outlet
part of the valve fluid channel. It can be particularly preferred
for the valve member to include a mandrel which is mounted on the
diaphragm so that it is displaced when the diaphragm expands, into
contact with the compressible tube. The compressible tube can be
located in a chamber in which the pressure can be changed as a
result of causing the valve fluid to flow between the inlet and
outlet sides of the valve fluid channel, especially by having the
chamber in fluid communication with the outlet side of the valve
fluid channel and by causing fluid to flow into the chamber.
[0048] The valve member in the valve of the invention can be
provided by a compressible tube which forms part of the primary
flow channel, the compressible tube being located within a chamber
which is in fluid communication with the outlet part of the valve
fluid channel so that an increase in fluid pressure in the said
chamber as a result of flow of valve fluid into the outlet part of
the valve fluid channel can cause compression of the compressible
tube, to reduce the flow of the primary fluid through the
compressible tube and to reduce the volume of the compressible
tube.
[0049] It can be preferred for the inlet part of the valve fluid
channel to be a closed chamber so that fluid flowing into or out of
the inlet part flows through the membrane. In this way, the valve
fluid is retained within the valve fluid channel and is not able to
mix with the fluid in the primary flow channel. This allows the
valve fluid to be selected to optimise the electro-osmotic flow
characteristics through the membrane component of the valve,
independent of the characteristics of the primary fluid.
[0050] However, when the primary fluid is able of exhibiting
electro-osmotic flow when subjected to a potential difference
across a membrane of a porous dielectric material, the inlet part
of the valve fluid channel can be arranged in communication with
the primary flow channel.
[0051] The valve of the invention can include a valve member
housing in which the valve member can move between its open and
closed positions. The valve member can be made to move between its
open and closed positions as a result of changes in pressure in the
valve fluid resulting from flow of valve fluid through the
membrane. The valve member housing can have a housing inlet and a
housing outlet which communicate with the primary flow channel so
that primary fluid flowing along the primary flow channel flows
through the valve member housing, through the said housing inlet
and housing outlet. When the valve member is in its closed
position, the capacity of the primary flow channel for flow of the
primary fluid is reduced compared with when the valve member is in
its open position. This can involve a reduction in the
cross-sectional area of the primary flow channel (and therefore
also a reduction of its volume). The primary flow channel can be
completely closed against flow of primary fluid or just partially
closed, when the valve member is in the closed position.
[0052] The valve member can provide a flow path for the primary
fluid to flow through the valve member housing, which can be
aligned with the housing inlet and the housing outlet when the
valve member is in the open position.
[0053] The primary flow channel can communicate with the valve
member housing so that primary fluid flowing along the primary flow
channel flows through the valve member housing, over, around or
through the valve member. Preferably, the direction of flow of
primary fluid through the valve member housing is generally
transverse to the direction in which the valve member moves, or
shuttles, between its open and closed positions. For example, when
the valve member moves along a shuttle axis, the housing inlet and
the housing inlet are each provided in a wall of the housing which
extends generally parallel to the shuttle axis. It can be
especially preferred for the housing inlet and outlet to be located
opposite to one another. However, other arrangements are envisaged,
according to the design of the flow path over, around or through
the valve member. For example, the flow path can be defined by a
region of the valve member with a reduced cross-section so that the
primary fluid flows over the surface of the valve member. The flow
path can be defined by an aperture extending through the valve
member so that the fluid flows through the valve member.
[0054] The flow of the primary fluid through the valve member
transversely to the direction in which the valve member moves has
the advantage that the valve member is not subject to pressure
differences in the primary flow channel, between the valve member
housing inlet and the valve member housing outlet.
[0055] Preferably, the valve member is a close fit within the valve
member housing so that a seal is formed between facing surfaces of
the valve member and the housing to minimise mixing of the primary
fluid and the valve fluid. Techniques for forming a sliding seal of
this general kind are known, including details of the tolerances
which are necessary to provide a seal while still allowing the
shuttle valve member to move within the housing.
[0056] Preferably, the valve member comprises a first part which is
a close fit in the housing so that fluid cannot readily flow
through the housing between the first part of the valve member and
the adjacent internal surface of the housing, and a second part
which has a reduced cross-section compared with that of the first
part, allowing flow of fluid through the housing around the second
part of the valve member. It will generally be preferred for the
cross-sectional shape of the first and second parts of the valve
member to be similar, with the area of the second part smaller than
that of the first part. For example, when the cross-sections of the
housing and the first part of the valve member are both rounded,
especially circular, the cross-section of the second part of the
valve member is preferably also similarly rounded, especially
circular, so that fluid can flow past the valve member around the
second part thereof. However, non-circular cross-sections can be
used, for example oval or rectangular. The use of non-circular a
cross-section for the housing and the valve part has the advantage
that alignment of a bore in the valve member and inlet and outlet
holes in the valve member housing is maintained.
[0057] Preferably, the shuttle valve member housing has a first end
towards which it moves when moving towards its open position from
its closed position and an opposite second end towards which the
valve member moves when moving towards its closed position from its
open position. Preferably, the valve member housing has a first
opening at or towards the first end thereof which communicates with
the inlet part of the valve fluid channel and a second opening at
or towards the second end thereof which communicates with the
outlet part of the valve fluid channel. This construction allows
latching of the valve member in a desired position by adjustment of
the potential difference across the membrane. The valve member can
be driven through the housing reversibly by appropriately changing
the polarity of the potential difference across the membrane. The
valve member can effectively be latched in a desired position
without the application of a potential difference while the
direction of flow of the primary fluid is generally perpendicular
to the direction in which the valve member moves.
[0058] One or both of the valve housing inlet and the valve housing
outlet can be located in a wall towards which or away from which
the valve member moves between the open and closed positions. For
example, one of the inlet and the outlet can be located in a wall
which extends parallel to the movement of the valve member, and the
other can be provided in an end wall. The opening in the wall which
is parallel to the movement of the valve member can be occluded by
the valve member when in the closed position, and partially or
completely opened when the valve member is in the open
position.
[0059] The performance characteristics of valves of the invention
which use a housing for a valve member can be changed by
appropriate selection of the dimensions of the valve housing and
the valve member. Parameters which can be changed include the
distance through which the valve member moves between the open and
closed positions of the valve (the "stroke"), and the
cross-sectional area of the housing (which will be approximately
the same as the valve member). A relatively short stroke, often in
combination with a relatively large cross-sectional area, can have
the advantage allowing larger forces to be generated to move the
valve member between its open and closed positions. This can be
appropriate when the fluid in the primary channel is at high
pressure. It can also facilitate fast operation of the valve. A
relatively long stroke can have the advantage of allowing
modulation of the flow of primary fluid through the valve.
[0060] The dimensions for a shuttle valve according to the
invention will be selected according to the intended application
and the space which will be available to accommodate it, and also
according to the quantity of the primary fluid that is required to
flow through the valve when in use and the pressure of that fluid.
The shuttle valve member can have a transverse dimension (which
will be a diameter when the valve member has a circular
cross-section) of at least about 0.5 mm, for example at least about
1.0 mm or at least about 2.0 mm. For many applications, the
transverse dimension will be not more than about 5.0 mm, for
example not more than about 4.0 mm or not more than about 3.0 mm.
For some applications, a smaller shuttle valve member can be used,
for example with a transverse dimension of not more than 1.0 mm,
preferably not more than 0.5 mm, especially not more than about 0.1
mm.
[0061] The materials used to make the shuttle valve member and the
valve member housing will be selected to be inert to liquids with
which they come into contact when the valve is in use, wear
resistance, ease of manufacture (to acceptable tolerances), low
friction. It can be convenient to form the housing from a polymeric
material, for example a polyolefin or a polycarbonate. This has the
advantage of being capable of manufacture using moulding
techniques. It also means that connections can be formed reliably
to one or both of the inlet and outlet parts of the valve fluid
channel. The shuttle can be formed from a metal, for example a
stainless steel. Losses due to friction in metal-polymer
combinations are low. The valve of the invention can be
manufactured from silicon based materials, for example using
semi-conductor wafer manufacturing methods.
[0062] The present invention provides a composite valve for
controlling flow of a primary fluid, which includes a primary valve
comprising a valve fluid channel, a membrane of a porous dielectric
material, first and second electrodes and a valve member, as
described generally above, and additionally a latching valve
comprising a shuttle valve member as described above.
[0063] The primary flow channel can include internal valves which
control the direction and rate of flow of liquid within it. A
one-way internal valve can be positioned in the tube on each side
of a valve according to the invention which can then function as a
pump driver in a fluid pump. Preferably, the primary flow channel
is provided at least in part by a compressible tube. The one-way
internal valve which is upstream of the driver valve can admit
fluid to flow as far as the downstream one-way internal valve.
Actuation of the driver valve causes liquid within the compressible
tube to be discharged through the downstream valve which opens due
to the increased internal pressure within the compressible
tube.
[0064] The valve of the invention can include means for biassing
the valve member towards a preferred position, which might be, for
example the position in which the valve is open to flow of the
primary fluid, or the position in which the valve is closed to flow
of the primary fluid. The provision of biassing means can provide
for safety feature for the event, for example, that the valve loses
power or some other failure. The biassing means can be provided by,
for example, a spring member, which acts on the valve member and
can be deformed resiliently when the valve member moves in the
normal operation of the valve.
[0065] Accordingly, in another aspect, the invention provides a
pump for controlling flow of a primary fluid in a primary flow
channel, which comprises:
[0066] a. a driver valve comprising:
[0067] i. a valve fluid channel,
[0068] ii. a membrane of a porous dielectric material located in
the channel so as to divide the channel into an inlet part and an
outlet part and so that valve fluid flowing between the inlet and
outlet parts flows through the said membrane,
[0069] iii. first and second electrodes located for electrical
communication with valve fluid in the inlet and outlet parts
respectively of the valve fluid channel for application of an
electric potential across the membrane in order to promote
electro-osmotic flow of valve fluid through the membrane,
[0070] iv. a valve member which can be displaced between open and
closed positions as a result of valve fluid moving in the valve
fluid channel through the membrane, into or out of the outlet part
of the valve fluid channel, in which the valve member causes a
reduction in the volume of the primary flow channel when it is in
the closed position compared with when it is in the open
position,
[0071] b. an inlet valve located upstream of the driver valve, for
controlling flow of primary fluid into the primary flow channel
where it is acted on by the driver valve, and
[0072] c. an outlet valve located downstream of the driver valve,
for controlling release of primary fluid from the primary flow
channel where it is acted on by the driver valve.
[0073] Features of the valve of the invention which are discussed
in this document can be incorporated in the driver valve of the
pump of the invention.
[0074] Preferably, the pump can preferably include a latching valve
to control flow of the valve fluid in the valve fluid channel. The
latching valve can be a shuttle valve according to this invention.
Preferably, one or each of the inlet valve and the outlet valve can
be a valve according to this invention. Preferably, one or each of
the inlet valve and the outlet valve includes a latching valve to
control the flow of valve fluid in the respective valve fluid
channel. The or each latching valve can be a shuttle valve
according to this invention.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0075] Embodiments of the invention will now be described by way of
example with reference to the accompanying drawings, in which:
[0076] FIG. 1a is a side view of a valve according to the invention
which is open to allow flow of primary fluid.
[0077] FIG. 1b is a side view of the valve shown, in FIG. 1a which
is closed to prevent flow of primary fluid.
[0078] FIG. 2a is a side view of another embodiment of valve
according to the invention which is open to allow flow of primary
fluid.
[0079] FIG. 2b is a side view of the valve shown in FIG. 2a which
is closed to prevent flow of primary fluid.
[0080] FIG. 3 is a side view of another embodiment of valve
according to the invention.
[0081] FIG. 4 is a side view of a further embodiment of valve
according to the invention.
[0082] FIG. 5a is a side view of another embodiment of valve
according to the invention.
[0083] FIG. 5b is a side view of the valve shown in FIG. 5a, which
is closed to prevent flow of primary fluid.
[0084] FIG. 6 is a side view of a further embodiment of valve
according to the invention.
[0085] FIG. 7a is a side view of a shuttle valve according to the
invention, with the shuttle valve member in the open position.
[0086] FIG. 7b is a side view of the shuttle valve member of the
valve shown in FIG. 7a, in the closed position.
[0087] FIG. 8a is a side view of another embodiment of shuttle
valve according to the invention, with the shuttle valve member in
the open position.
[0088] FIG. 8b is a side view of the shuttle valve member of the
valve shown in FIG. 8a, in the closed position.
[0089] FIG. 9 is a side view of another embodiment of shuttle
valve.
[0090] FIG. 10 is a side view of a pump which incorporates a valve
according to the invention.
[0091] FIG. 11a is a side view of another embodiment of pump.
[0092] FIG. 11b is an isometric view of the pump shown in FIG.
11a.
DETAILED DESCRIPTION OF THE INVENTION
[0093] Referring to the drawings, FIG. 1 shows a valve 2 for
controlling flow of a primary fluid in a primary flow channel. The
primary flow channel is defined by a baffle 4 and a conduit wall
6.
[0094] The valve includes a channel 8 which contains a quantity of
a valve fluid 10. The valve fluid channel 8 comprises two tubular
parts 12, 14, located on opposite sides of a membrane 16 which is
formed from a porous dielectric material. The porous dielectric
material can be, for example, an aluminium oxide ceramic which has
been rendered porous. Details of suitable materials, and of
techniques for rendering them porous, are known. Each of the tubes
12, 14 is bonded to the membrane 16 by adhesive bonding. Adhesive
can be provided between the external surface is of lugs on the
membrane which extend into the tubes, and the internal surfaces of
the tubes.
[0095] Each of the tubes 12, 14 is formed from a rigid polymeric
material which is compatible with the valve fluid and the primary
fluid. Examples of materials from which the tubes might be formed
include metals (especially stainless steel) and polymers (for
example, polyamides, polyesters, polycarbonates, polyolefins etc).
The thickness of the tube should be sufficient to ensure that the
tube does not distort in use when subjected to normal operating
pressures of the valve.
[0096] Each of the tubes has a constant cross section. Each of them
is closed at its free end (remote from the membrane). The tubes can
be closed by bonding a plain wall to the tube section, for example
using an adhesive, or by welding.
[0097] Each of the tubes has a series of holes formed in it towards
its free end. For example, each of the tubes might have six holes
formed in it, arrayed uniformly around its circumference.
[0098] Each of the tubes has a tubular sleeve 20, 22 bonded to its
external surface so as to cover the holes 18 and to provide a
fluid-tight seal to prevent loss of valve fluid. Each of the
sleeves is formed from a resiliently deformable elastomer which can
stretch to accommodate valve fluid in the space between it and the
external surface of the respected tube.
[0099] Each of the tubes 12, 14 includes an electrode 24, 26 which
is located on the respective face of the membrane, 16. The
electrodes are arranged for connection to a DC power source.
[0100] The valve fluid channel 8, comprising the tubes 12, 14 and
the membrane 16 is mounted with respect to the baffle 4 so that the
tube 14 extends through the baffle and is sealed to it. The seal
prevents flow of primary fluid through the baffle from the primary
flow channel. Applying a potential difference across the membrane
of porous material 16, by means of the electrodes 24, 26 causes the
valve fluid 10 to flow between the inlet tube 12 of the valve fluid
channel and the outlet tube 14. The volume of fluid within the
valve fluid channel (including that between the external surfaces
of the tubes 12, 14 and the tubular diaphragm sleeves, 20, 22)
remains constant. The application and the potential difference
across the membrane 16 of dielectric material determines the
distribution of liquid between the inlet tube 12 and the outlet
tube 14. Changes in the volume of liquid in either of these tubes
is accommodated by expansion of the space between the tubular
diaphragm sleeves 20, 22 and the adjacent external surface of the
respective tube.
[0101] In FIG. 1a, there is relatively more of the valve fluid on
the inlet side 12 of the membrane 16, compared with the volume of
fluid on the outlet side 14. As a result, the tubular membrane
diaphragm 22 is not stretched, and has a low profile close to the
surface of the tube 14. In contrast, the tubular sleeve membrane 22
on the inlet side is expanded to accommodate valve fluid. This is
as a result of the application of a potential difference across the
electrodes 24, 26.
[0102] With the tubular diaphragm sleeve 22 contracted, primary
fluid is able to flow through the primary flow channel, in the
space between the external wall 6 of the flow channel and the valve
2. This is as shown in FIG. 1a.
[0103] In FIG. 1b, the potential difference applied across the
electrodes 24, 26 is reversed, causing valve fluid to flow from the
inlet side 12 of the membrane 16 to the outlet side 14. This allows
the tubular diaphragm sleeve 20 on the inlet side to contract,
while the tubular membrane diaphragm 22 on the outlet side expands
to accommodate migrating valve fluid. The tubular diaphragm sleeve
22 on the outlet side expands until it contacts the internal
surface of the wall 6 of the primary flow conduit, to form a seal
between it and the valve 2. This cuts off the flow of primary fluid
in the primary flow conduit. The valve is therefore closed.
[0104] The valve can revert to the open configuration shown in FIG.
1a from the closed configuration shown in FIG. 1b by once again
reversing the potential difference across the electrodes 24,
26.
[0105] FIG. 2 shows another construction of valve in which the
membrane of porous dielectric material 50 is formed as part of a
baffle 52. As in FIG. 1, the baffle together with a wall 54 defines
a flow conduit 56 for a primary fluid.
[0106] A valve fluid channel is provided, defined by the membrane
50 of the porous dielectric material and spaces on each side of the
baffle 52 which are defined by deformable diaphragm seals 58,
60.
[0107] Electrodes 62, 64 are provided on opposite sides of the
baffle 52, so that they are in contact with valve fluid contained
in the spaces between the baffle 52 and the respective diaphragm
seal 58, 60.
[0108] The application of a potential difference across the
membrane 50 by means of the electrodes 62, 64 can cause valve fluid
to move from the inlet side of the membrane (defined by the
diaphragm seal 58) to the outlet side (defined by the diaphragm
seal 60).
[0109] As shown in FIG. 2a, valve fluid is located primarily on the
inlet side of the membrane. Primary fluid is therefore able to flow
the primary flow channel 56.
[0110] As shown in FIG. 2b, valve fluid is located predominantly in
the outlet side of the membrane. This causes the membrane to swell,
to contact opposite faces 66 of the flow channel. The orifice
provided by the outlet limb 68 of the flow channel is closed as a
result of action against it of the diaphragm seal 60.
[0111] FIG. 3 shows a valve for controlling flow of a primary fluid
in a primary flow channel 80. The primary flow channel comprises a
compressible tube. The use of compressible tubes for conducting
liquids is well known, especially in medical applications. Examples
of suitable materials include, for example, polyurethanes,
silicones and the like. The primary flow channel is located
adjacent to a support 82.
[0112] The valve includes an electro-osmotic pump which includes a
membrane 84 formed to make porous dielectric material, and inlet
and outlet tubes 86, 88. The membrane and the inlet and outlet
tubes together form a valve fluid channel, which contains a
quantity of a valve fluid 90.
[0113] The free end of the inlet tube 86 is closed by means of a
flexible diaphragm seal 92. The free end of the outlet tube 88
includes a bellows 94, having a mandrel 96 attached to it at the
end which faces the compressible tube 80 of the primary flow
channel.
[0114] Electrodes 98, 100 are included in the valve fluid channel
in contact with liquid in the inlet and outlet tubes 86, 88.
[0115] The application of a potential difference across the
membrane 84 causes valve fluid to flow between the inlet and outlet
tubes 86, 88. The configuration of the diaphragm seal 92 at the
inlet end is able to change to accommodate the change of valve
fluid in the inlet tube.
[0116] Similarly, the bellows 94 on the outlet tube 88 is able to
expand to accommodate an increase in the volume of valve fluid in
the outlet tube 88.
[0117] Expansion of the bellows 94 leads to movement of the mandrel
96 towards the compressible tube of the primary flow channel.
Continued movement of the mandrel causes compression of the tube,
leading to a reduction in the rate of flow of primary fluid.
[0118] Valve fluid can be made to flow in the reverse direction so
as to withdraw the mandrel from the compressible tube, opening the
primary flow channel to flow of primary fluid. This can be
accomplished by reversing the polarity of the potential difference
applied across the membrane 84.
[0119] The outlet tube 88 is mounted in a baffle 102. The baffle
102 is fixed spatially relative to the support 82 and the
compressible tube 80 of the primary flow channel.
[0120] FIG. 4 shows a valve in which the valve fluid and the
primary fluid are in fluid communication with one another and have
the same composition. This of course requires that the primary
fluid whose flow is to be controlled by the valve of the invention
is capable of participating in electro-osmotic flow.
[0121] As in the valve shown in FIG. 2, the valve shown in FIG. 4
comprises a membrane 120 of a porous dielectric material which is
embedded in a baffle 122. A diaphragm seal 124 is provided on the
outlet side of the membrane. Electrodes 126, 128 enable a potential
difference to be applied across the membrane 120.
[0122] The valve does not include a diaphragm seal on the inlet
side: instead, the inlet side of the membrane is exposed to primary
fluid which flows towards the primary fluid outlet 130 through
openings 132 in the baffle 122.
[0123] The application of a potential difference across the
membrane 120 can be relied on to cause valve fluid (which is the
same as the primary fluid) to flow through the membrane into the
space between the membrane and the diaphragm seal 124. The
diaphragm seal is then able to close the outlet conduit 130 to
prevent flow of primary fluid.
[0124] FIG. 5a shows a valve in which the valve member comprises a
diaphragm 140 which is provided on the end 142 of a valve fluid
channel 144. The valve fluid channel has a membrane 146 of a porous
dielectric material provided in it, with associated electrodes, as
discussed above. The valve fluid channel includes an expandable
reservoir 147 at its inlet end. The diaphragm is located within a
chamber 148 which has an inlet 150 for the primary fluid and two
outlets 152, 153. As shown in FIG. 5a, the diaphragm is in its open
position in which it is uninflated, where fluid is able to flow
between the inlet 150 to the chamber and the two outlets. As shown
in FIG. 5b, the diaphragm is in its closed position in which it is
inflated (in the manner of a balloon), so that the inlet 150 and
the outlet 153 are blocked by the diaphragm, preventing flow of
fluid between the inlet 150 and each of the outlets 152, 153. Note
that the chamber can be modified to have more than one inlet, or
one or more outlets. The valve could be modified to include more
than one diaphragm, or to include more than one electro-osmotic
device.
[0125] As shown in FIGS. 5a and 5b, the illustrated valve includes
a latching valve 154, which can be a shuttle valve of the kind
described below with reference to FIGS. 8 and 9.
[0126] FIG. 6 shows a valve according to the invention in which the
valve member comprises a compressible tube 160 which forms part of
the primary flow channel 162. The compressible tube is located
within a chamber 164 which is in fluid communication with the
outlet part of the valve fluid channel 166. The valve fluid channel
includes a membrane 168 of porous dielectric material, with
associated electrodes 170, to cause fluid to flow between the
outlet part of the channel and an inlet part 172. Accordingly, an
increase in fluid pressure in the said chamber as a result of flow
of valve fluid into the outlet part of the valve fluid channel, due
to the application of a potential difference across the membrane
168 can cause compression of the compressible tube, to reduce (or
to close completely) the flow of the primary fluid through the
compressible tube 160.
[0127] FIG. 7a shows a valve 180 which comprises a valve member 182
which can slide within a chamber 184 which defines a valve member
housing. The chamber has an inlet 186 and an outlet 188 for the
primary fluid. The chamber is in communication with the outlet part
189 of the valve fluid channel, which contains a membrane 190 of a
porous dielectric material and associated electrodes 191. The valve
fluid channel includes a resiliently expandable reservoir 192 for
valve fluid at its inlet end. The valve member is able to slide
between its open position as shown in FIG. 7a in which the inlet
186 is open, allowing fluid to flow through the chamber from the
inlet 186 to the outlet 188, to the closed position as shown in
FIG. 7b in which the inlet 186 is closed. With appropriate fine
control of the position of the valve member, the inlet can be
closed partially by locating the valve member so that it only
partially covers the inlet.
[0128] FIGS. 8 and 9 relate to a construction of valve in which
valve fluid on both the inlet and outlet sides of a membrane acts
on a valve member, which can move in a reciprocating (or shuttle)
action in a valve member housing.
[0129] The valve shown in FIG. 8a includes a shuttle valve member
200 which is able to slide within a valve member housing 202. The
valve member housing is moulded from a polycarbonate material. The
shuttle valve member is made from stainless steel. The valve member
housing is connected at each of its opposite ends to the inlet and
outlet tubes 204, 206 of an electro-osmotic flow device of the kind
described above. The valve is used to control flow of primary fluid
through a primary flow channel which is defined by a tube 208 which
communicates with the interior of the valve member housing 202.
[0130] The valve shown in FIG. 8a includes a membrane 210 which has
electrodes in contact with valve fluid in the inlet and outlet
tubes 204, 206. Application of a potential difference across the
membrane 210 causes migration of valve fluid across the membrane
210, changing the relative amounts of the valve fluid in the inlet
and outlet tubes 204, 206. This change in the distribution of the
valve fluid is accommodated by movement of the shuttle valve member
200 within the valve member housing 202.
[0131] The shuttle valve member has a cylindrical form with a round
cross-section, and is a close sliding fit within the valve member
housing. A portion 220 of the shuttle valve member has a reduced
diameter so that there is an annular space in that region of the
shuttle valve member, between its external surface and the internal
surface of the valve member housing. The distance of this reduced
diameter portion from the end of the shuttle valve member is the
same as the distance from one end of the valve member housing to
the primary flow channel 208. Accordingly, when the shuttle valve
member is at the limit of its movement in one direction within the
valve member housing, the reduced diameter portion 220 is aligned
with the primary flow channel, allowing the primary fluid in the
primary flow channel to flow around the shuttle valve member,
through the valve member housing. In another embodiment, the
shuttle valve member can have an opening extending through it in
the form of a bore, which is aligned with the primary flow channel
when the valve member is in its open position.
[0132] Movement of valve fluid from the outlet tube 206 to the
inlet tube 204, through the membrane 210, causes the shuttle to
move from the open configuration shown in FIG. 7a towards the
closed configuration shown in FIG. 7b. As shown in FIG. 7b, the
reduced diameter portion 220 is displaced relative to the flow
channel 208, shutting the flow channel 208 against flow of primary
fluids.
[0133] The embodiment of the shuttle valve member and valve member
housing shown in FIG. 9 has different dimensions. The
cross-sectional area of the shuttle valve member is larger. The
distance through which it moves (represented by the free space
between the end of the shuttle valve member and the valve member
housing) is smaller. The length of the reduced diameter portion 220
of the shuttle valve member is less. This construction of valve
member and housing enables larger forces to be generated to move
the shuttle valve member within the housing.
[0134] A composite valve according to the invention can comprise a
primary valve which is used to control the flow of the primary
fluid, as discussed above: certain primary valve constructions (for
example as shown in FIGS. 1 to 7 above) are susceptible to
reverting from the closed configuration towards or to the open
configuration due to pressure of fluid in the primary flow channel.
It can be desirable to latch the primary valve in its open position
or in its closed position. This can be achieved by means of a
latching valve. A shuttle valve such as those shown in FIGS. 8 and
9 can be used as a latching valve in a composite valve. When a
shuttle valve is used as a latching valve, the primary fluid for
the purposes of the shuttle valve is the valve fluid for the
primary valve, so that moving the shuttle valve between open and
closed positions allows flow of the valve fluid for the primary
valve to flow in the respective valve fluid channel, to move the
valve member to close or to open the valve. However, the flow of
this valve fluid is only possible when the shuttle latching valve
is open.
[0135] Accordingly, a shuttle valve, for example as shown in FIG. 8
or FIG. 9, can be incorporated with a primary valve, for example as
shown in any of FIGS. 1 to 7, to form a composite valve.
[0136] FIG. 10 shows a pump construction which is based on the
valve shown in FIG. 3. All of the features of the valve fluid
channel and the deformable diaphragm and bellows are as described
above in relation to FIG. 3.
[0137] The compressible tube 80 includes a first one-way flow valve
250 which is located upstream of the mandrel 96, and a second
one-way flow valve 252 which is located downstream of the mandrel
96. This valve assembly can be used to pump fluid. When the space
254 between the one-way valves 250, 252 is full of primary fluid,
the valve fluid can be pumped into the outlet tube 88, causing the
mandrel 96 to compress the tube. The one-way valve 250 remains
closed as the tube is compressed, and the one-way valve 252 opens,
allowing primary fluid in the space 254 to be ejected from that
space.
[0138] When the potential difference across the membrane 84 is
reversed so that the mandrel is withdrawn, the volume of the space
254 in the compressible tube increases. This draws primary fluid
into the said space. Valve 252 closes and valve 250 opens.
[0139] Repeated movement of the mandrel 96, inwardly and outwardly
relative to the compressible tube 80, causes controlled quantities
of the primary fluid to be discharged repeatedly from the
compressible tube 80.
[0140] FIGS. 11a and 11b show a pump which comprises a tubular
housing 300 which contains a flow channel 302 for a primary fluid.
The flow channel is provided within the housing 300 by a
compressible tube. The tube can be compressed in three axially
spaced regions of the housing.
[0141] The pump includes three valves 304, 306, 308 of the kind
discussed generally above, arranged along the housing. Each of them
comprises a valve fluid channel 310 containing a membrane 312 of a
porous dielectric material, and having an inlet end 314 with a
reservoir for the valve fluid, and an outlet end 316 which
communicates with the housing 300. Each of the valves 304, 306, 308
can be operated in the manner of the valve shown in FIG. 6. When
each of the valves is in the open configuration, its valve fluid is
biassed towards the inlet end of the valve fluid channel. When each
of the valves is in the closed configuration, its valve fluid is
biassed towards the outlet end of valve fluid channel. It then
compresses the compressible tube 302 within the housing 300 in one
of the spaced apart regions thereof in which the tube can be
compressed.
[0142] The central one 306 of the three valves includes a shuttle
latching valve 309. The latching valve a shuttle valve member 310
which is able to slide within a valve member housing 313. The valve
member housing is moulded from a polycarbonate material. The
shuttle valve member is made from stainless steel. The valve member
housing is connected at each of its opposite ends to the inlet and
outlet tubes 324, 326 of an electro-osmotic flow device of the kind
described above. The valve is used to control flow of the valve
fluid of the central valve 306 through the respective channel 310,
which communicates with the interior of the tubular housing 300, in
which the valve member provided by the compressible tube 302 is
located.
[0143] The shuttle latching valve includes a membrane 320 which has
electrodes in contact with valve fluid in the inlet and outlet
tubes 324, 326. Application of a potential difference across the
membrane 320 causes migration of valve fluid across the membrane,
changing the relative amounts of the valve fluid in the inlet and
outlet tubes 324, 326. This change in the distribution of the valve
fluid is accommodated by movement of the shuttle valve member 310
within the valve member housing 313.
[0144] The pump shown in FIGS. 11a and 11b is operated cyclically.
Initially, all three of the valves 304, 306, 308 are in their
closed positions, with the compressible tube 302 within the housing
300 compressed in each of the spaced apart regions thereof in which
the tube can be compressed.
[0145] The upper valve 304 is then opened to admit flow of the
primary fluid, and the central valve 306 is then opened to admit
the primary fluid into the compressible tube 302, in the central
region of the housing 300. The upper valve 304 is then closed to
prevent flow of primary fluid. The lower valve 308 is then opened,
and the central valve closed. Closing the central valve causes
fluid in the compressible tube 302, in the central region of the
housing 300, to be expelled from the compressible tube.
[0146] The latching valve which forms part of the central valve 306
can be relied on to latch the central valve in its open position or
its closed position as required. Similar latching valves can be
incorporated with one or both of the upper and lower valves 304,
308.
[0147] With any two of the valves 304, 306, 308 of the pump in
their open positions, the third valve can be used to control the
flow of the primary fluid.
* * * * *