Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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A TITLE OF THE INVENTION
"A Pump"
BACKGROUND TO THE INVENTION
This invention relates to a pump. More particularly the present invention
relates to a
membrane pump.
Pumps, which incorporate a flexible element to achieve the pumping action, are
known.
For example, the flexible element can be in the form of a deformable tube. A
pump of
this type is described in our international patent specifications WO 99/01687
and WO
02/18790.
In WO 02/1890 there is described a pneumatic pinch mechanism for a deformable
tube
and, in particular, the mechanism when applied to the pump. The mechanism
includes
a piston movably located within a chamber with vent means so that at some
point
during a movement of the piston between the first and second positions, a
pressure
equalisation occurs within the chamber. Consequently, as the piston moves
toward the
first position a pressure increase occurs which can be used to deform the
deformable
tube. When the piston moves toward the second position, a negative pressure is
created
which can be used to return the deformable tube from its deformed
configuration.
The pump has proved successful, but as with deformable tube pumps, the
deformable
tube can require regular replacement. This is generally due to the repeated
closing and
release of the tube leading to localised wear or fatigue in the tube, which
can ultimately
lead to the tube rupturing.
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A further disadvantage with such pumps is that it is often difficult or not
possible to
produce a deformable tube (having the necessary characteristics of being able
to deform
and rebound or be returned to its non-deformed state) from a material, which
is
particularly suited for handling the materials intended to flow through the
pump.
A membrane pump therefore provides an advantage that the membrane can be
formed
from a material, which has a wide range of applications, and indeed materials
which are
required in some applications, but which cannot be formed or economically
formed into
replaceable deformable tubes for use in pumps having cyclic deforming of the
tube.
However, membrane pumps to date are of constructions, which still give rise to
mechanical stress in the diaphragm, thereby requiring regular replacement of
the
diaphragm. Also, many known diaphragm pumps fall short in performance,
especially in
achievement of full removal of fluid from the pump chamber on the exhaust
stroke and
full uptake on the inlet stroke.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a membrane pump,
which is
of a construction resulting in reduction in mechanical stress in the membrane,
thereby
leading to longer membrane life.
It is a further object of the present invention to provide a membrane pump of
a
construction, which enables full removal of fluid on the exhaust stroke and
fuller uptake
on the inlet stroke during operation of the pump.
Broadly according to one aspect of the invention there is provided a pump
including a
cavity with an inlet port and an outlet port opening into and from the cavity,
a flexible
membrane located within the chamber and arranged to be bi-stable in two states
corresponding to completion of inlet and exhaust of a pumping cycle.
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Preferably the flexible membrane is mounted in the cavity with a preset
whereby the
membrane adopts one of the stable states.
The membrane is preferably formed from an elastomeric material which can be in
sheet
form.
In a preferred form the membrane is clamped between first and second housing
sections, each section having a cavity section such that when the housing
sections are
assembled to form a housing, said cavity is formed.
The cavity is, in the preferred form, located in a housing, the cavity being
connectable to
a source or sources of negative and positive pressure and means to cyclically
apply the
positive and negative pressures to the cavity to cause the membrane to move
between
the stable states.
In a preferred form the first and section housing sections configured to form
said cavity
when the housing sections are joined together, clamp the membrane about a
peripheral
margin thereof.
The first housing section can include a recess into which the membrane is
located, the
peripheral dimensions of the membrane being greater than those of the recess
whereby
compressive forces are set up in the membrane when it is installed in the
recess.
The second housing section can include a protruding portion which engages in
the
recess, when the first and second housing sections are combined together, to
cause the
membrane to be clamped in place.
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Preferably there is a third housing section coupled to the second housing
section, said
third housing section including means for facilitating connection of inlet and
outlet
conduits for pumpable material.
In a preferred form the second and third housing sections include inlet and
outlet
openings and means for locating therein a valve element. The valve element can
be a
disk of flexible material.
Preferably the cavity is elongate and of curved cross-section, a port via
which the
sources) of positive and negative pressure are connectable opens into the
cavity.
The ends of the elongate cavity are preferably complex curved.
BRIEF DESCRIPTION OF THE DR?~WINGS
In the following more detailed description of the invention according to one
preferred
embodiment, reference will be made to the accompanyin g drawings in which:-
Figure 1 is a longitudinal cross-section through the pump,
Figure 2 is an exploded view in cross-section of t he pump as shown in Figure
1,
Figure 3 is a transverse cross-sectional view taken between the inlet and
outlet
ports but showing only two sections of the pump body,
Figure 4 is a perspective view of one housing section of the pump,
Figure 5 is a schematic view of the pump on an exhaust cycle,
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Figure 6 is a view similar to Figure 5 but of the inlet cycle, and
Figure 7 is a cross-sectional view of a second embodiment which incorporates a
different form of control mechanism.
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DETAILS DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
Referring firstly to Figures 1-3, the pump 10 is, according to a preferred
embodiment,
formed of two housing sections 11 and 12. When these are assembled together
they
define an internal pump cavity 13. Clamped between the housing sections 11 and
12,
as will hereinafter be described, is a membrane 14 which is made from a
suitable
flexible material.
In the preferred form of the invention, the cavity 13 is elongate and, as
shown in Figure
4, each end 15 is complex curved. In cross-section as shown in Figure 1, each
end is
also curved as indicated at 15. Furthermore, in transverse cross-section as
shown in
Figure 3, the cavity 13 is also of curved cross-section.
Housing section 11 incorporates a rebate 16, which effectively results in an
upstand or
projecting portion 17. Thus, the cavity section 13a is effectively located, at
least in part,
in the resultant upstanding portion 1 7.
The other housing section 12 has a recessed portion 1 ~ with cavity section
13b
extending away from the floor of the recess 1 S. Thus, when the two housing
sections
1 1 and 12 are brought together the projecting portion 17 engages snugly
within recess
18. However, the arrangement is such that surface 20 of projecting portion 17,
terminates a distance from the floor 19 of recess 18. In the preferred form of
the
invention, this distance D (see Figure 1) is less than the thickness of the
membrane 14.
The reason for this gap D will hereinafter become apparent.
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The membrane 14 is, in the preferred form of the invention , cut from sheet
material.
The material is elastomeric and of a type which is compatible with the
material, that is
intended to be pumped through the pump 10. For example, if the material to be
pumped through the pump 10 is corrosive, then the membran a material is
selected such
as to be able to withstand the corrosive nature of the fluid. By way of
further example,
the membrane is selected from a food grade material in the event that the pump
is to
handle a liquid foodstuff.
The various types of materials and applications to which a pump of this type
can be put
are well Known to those sleilled in the art. Therefore further description
herein is not
necessary for the purposes of describing the construction and operation of the
pump
according to the invention.
According to the invention, the membrane 14 is cut in a sl-iape and to a size,
which
enables it to be snugly fitted into the recess 18. However, the overall
peripheral
dimensions of the membrane 14 are greater than the peri pheral dimensions of
the
sidewall 21 of the recess 18. Thus, when the membrane 14 is placed into the
recess 18
compressive forces are set up in the membrane due to what is effectively an
interference
fit of the membrane 14 into the recess 18. This therefore causes membrane 14
to
deform from its flat state into a state, which essentially conforms with the
complex
curved shape of the cavity section 13b. Effectively, the membrane 14 is
mounted with a
preset.
However, when the housing section 11 is combined with housing section 12 (the
membrane 14 being in place in recess 18) the fact that di stance D is less
than the
thickness of the membrane 14 causes the peripheral edge margin portion of the
membrane 14 to be sandwiched and clamped between opposing surfaces 19 and 20.
This clamping force provides yet further compressive forces in the membrane,
which
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causes the membrane to even more closely adapt into the shape of the cavity
section
13b. Thus, in effect the membrane 14 is in contact with, or located closely
adjacent to
the overall surface of the cavity section 13b.
A port 22 is formed in the housing section 12 and opens into the cavity
section 13b.
This port 22 can be offset toward one end of the cavity 13, as shown in the
drawings, or
else it can be located midway in the length of the cavity 13.
In one form of the invention, a narrow groove 22a can be formed in -the wall
surface of
the cavity section 13b and extend along the length of the cavity 13 either
side of from
the port 22. Also a similar narrow groove (not shown) can be formed in cavity
13b. The
effect of the narrow grooves) is to prevent the pump from "choking" when the
membrane approaches contact with the surface of the cavity. Such contact could
prevent fluid flow from occurring and thereby result in the cavity not fully
filling or
exhausting. The narrow groove ensures that flow occurs right d own to when the
membrane comes into full overall contact with the cavity surface.
At each end of the cavity section 13a is a port, which opens from tl-~e cavity
13 to the
outer surface 23 of housing section 1 1. Port 24 functions as an inlet port
while port 25
functions as an outlet or exhaust port. Each of inlet ports 24 and exhaust
port 25 can,
as shown, be made up by a plurality of separate passages 24a and 2 5a
respectively. A
recess 26 is formed in the surface 23 of housing section 1 1 and into this is
engaged a
disk of flexible material which forms valve element 27. Likewise, a calve
element 28 in
the form of a disk of flexible material is provided in the exhaust valve 25
but it locates
in a recess 29 in cover 30.
Cover 30 has connecting pieces 31 and 32 (e.g. in the form of annul ar walls
or turrets)
which respectively provide connections for an inlet line (not shown) to inlet
valve 24 and
an outlet or exhaust line (also not shown) from exhaust valve 25.
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The arrangement of the membrane 14 in the cavity 13 as described above,
results in the
membrane 14 being bi-stable. One stable position of the membrane 14 is shown
in full
detail in Figure 1 while the other stable position is shown in dotted detail.
Thus, in the
first stable position the membrane 14 is in the cavity section 13b and when in
the
second stable position the membrane 14 is located in the cavity section 13a.
In effect
therefore, the membrane 14 adopts a stable position in either a position which
conforms with completion of intake of fluid through inlet valve 24 (i.e. the
position
shown in the drawings) and a full or completed exhaust position.
The membrane 14 is moved between its two stable positions by application of
negative
P1 and positive P2 pressures applied to the cavity 13b through port 22.
Consequently
with the pump in the configuration shown in Figure 1 and inlet and outlet
conduits or
lines attached to connectors 31 and 32 a positive pressure P2 (see Figure 5)
applied
through port 22 will force the membrane 14 into an opposite stable position.
In this
"stroke" of the membrane 14, the inlet valve 24 is forced closed while the
outlet valve 25
is forced open and any fluid within the cavity 13 i.e. to that side of the
membrane
opposite to that which faces port 22, is exhausted through the outlet valve
25.
Upon this "stroke" having been completed a negative pressure P1 applied via
port 22
(see Figure 6) causes the membrane 14 to return to the position shown in
Figure 1
which also causes the exhaust valve 25 to close but the inlet valve 24 to open
and
enable fluid in the inlet line to be drawn into cavity 13. The cavity 13 thus
fills with the
fluid ready to be exhausted through.the outlet valve 25 upon the next cycle
occurring
when membrane 14 moves back into cavity section 13a under positive pressure
P2.
The means for applying negative and positive pressures can take on many forms
as will
be apparent to the person skilled in the art. The means could comprise, for
example,
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sources of positive and negative pressure, which via suitable valves can be
coupled to
the port 22.
Examples of mechanisms we have developed for applying the positive and
negative
pressures via port 22 are shown in Figures 1 and 7.
As shown in Figure 1, there is a pneumatic operator 33 that has a body 34 wh
ich defines
a chamber 35 in which a piston 36 is reciprocally mounted. A piston rod 37 is
pivotally
connected via pivot 38 to the piston 36. This piston rod 37 is pivotally
cor~nected by
pivot 39 at its other end to a rotating drive member 40. The drive member 40
is
connected to a drive means (not shown) which can be in the form of an electri
c motor or
some other form of motive power.
A port 41 in the end wall 42 of the body 34 is in communication with port 22.
As shown
in Figure 1 the body 34 is in close proximity to the pump 10 but it will be
appreciated
by those skilled in the art that the pneumatic operator 33 could be located
quite some
distance away from the pump 10 and connected by a conduit extending between
ports
22 and 41.
A recess 43 is formed in the inside surface of the side wall 34a of body 34.
The recess
is located adjacent the end of wall 42.
At a position in the length of the side wall 34a of the body 34 there is a
port 43a which
opens to atmosphere. As illustrated, the port 43a is shown in one preferred
position
where it is adjacent the inner end of the piston 36 when the piston is at its
full stroke
away from end wall 42 of body 34. Thus, once the piston has moved past the
port 43a
(i.e. into the position of Figure 1) the chamber 35 is fully vented to
atmosphere. The
position of port 43a can be varied dependent on use requirements that may
require
venting before the full stroke of piston 36 has been completed.
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Consequently, when the piston 36 advances toward end wall 42 the air in
chamber 35
becomes compressed and the resultant positive pressure P2 works on the
membrane 14
to force it into cavity section 13a. However, when the piston 36 has completed
its
5 stroke toward wall 42 the piston sealing ring 36a is positioned within the
area of the
recess 43 whereby air can flow past the sealing ring 36a and exhaust through
the
clearance between the piston 36 and surface of wall 36a.
Upon its reverse stroke commencing the piston 36 moves so that sealing ring
36a
10 moves away from recess 43 and once again seals against the entire
peripheral surface of
wall 36a. Consequently, the movement of the piston creates negative pressure
P1 until
the port 43a opens to vent the chamber 35 to atmosphere and hence complete the
pumping cycle.
An alternative arrangement is shown in Figure 7.
A port 43' in the wall 34a is connected to a conduit 44 which is, in turn,
connected to a
vent housing 45. One wall of the vent housing 45 has a vent opening 49 which
opens
into a chamber 50 in which a pin 51 is moveably located. The pin 51 is
therefore
moveable between the position where conduit 44 is isolated from vent 49 to a
position
where the vent 49 is connected to conduit 44.
Mounted with a periphery of the driving member 40 and projecting there from is
a pair
of curved or shaped (e.g. tamped) projections 52 and 53. Consequently, as the
rotating
member 40 rotates, a projection 52 or 53 comes into contact pin 51 which
forces the
pin 51 inwardly (relative to the housing) thereby connecting or disconnecting
the vent
49 from the conduit 44.
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This action causes the chamber 35 to vent to atmosphere (via vent 49) for the
period of
time that the pin 51 fails to seal closed the conduit 44. In the preferred
form of the
invention the pin 51 is biased by suitable biasing means (not shown) such as a
spring or
the like into a position where the vent 49 is closed i.e. isolated from
conduit 44.
As a consepuence, continued movement of the piston 36 creates a positive
pressure
build up which via port 22 forces the membrane 14 from the position shown in
Figure 7
to its other stable position in cavity section 13a. Material resident in the
cavity 13 is
thus forced out through the exhaust port 25.
As the piston 36 moves back along the chamber 35 from the second position the
vent
port 49 will still be closed. This will continue to be the situation until the
engagement
projection 52 comes into contact with pin 51 to effectively open the vent port
49. As a
result, the vent port 49 once again vents the chamber 35 to atmosphere. After
the vent
49 is closed from conduit 44 by movement of the pin 51 and as a result of the
pin
clearing the projection 52, the continued movement of the piston 36 back to
its first
position will create a negative pressure.
This negative pressure build up will cause the membrane 14 to move back to the
~0 position shown in Figure 7 thereby creating a negative pressure within the
chamber 13
which draws pumpable medium on the inlet 24 to be drawn through the inlet
valve 24
and into the cavity 13. This inflow will continue until the membrane 14 is
fully bacle into
its position shown in Figure 7.
Preferably the point and the movement of the piston 36 where contact between
the pin
51 and projections 53 respectively occurs is adjustable. According to the
preferred
form of the invention, projections 52 and 53 can be adjustable in position on
the
periphery of the driving member or rotor 40 so that, for example, the period
during
which the piston creates a positive pressure could be less. This would result
in the time
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that the membrane is under negative pressure to be greater than the period
that it is
under positive pressure.
The bi-stable flexible membrane 14 effectively has a small amount of travel
between its
two states. It is not mechanically connected to any drive thereby giving the
membrane
free movement in the cavity 13. The cavity shape is round rectangular and its
contoured
to fit the bi-stable shape of the membrane. Consequently, the cavity supports
the
diaphragm over its full surface when the diaphragm is in a so-called stable
state. The
membrane is therefore subject to uniform pressure not only when in the stable
states
but during the transition between the states as it is supported on both
surfaces by the
incoming or outgoing pumpable medium and the positive or negative pressure
applied
across the whole membrane surface via port 22.
It is believed that the bi-stable nature of the membrane, the cavity shape and
contour,
as well as the uniform pressure to which the membrane is subjected will lead
to a
significant reduction in mechanical stress on the membrane. This will
therefore equate
to longer membrane life. Furthermore, during operation of the pump there will
be full
removal of fluid on the exhaust stroke and full uptalee on the inlet stroke as
the
membrane 14 moves fully from contact and support within the two sections of
the
chamber.
The pump therefore provides maximum efficiency and good linear flow
characteristics,
the latter being more critical as viscosity of the pumpable medium increases.
The outlet
pressure will be governed by the drive pressure therefore no need for pressure
limiting.
Suction (lift) is governed by the negative pressure. There is thus consistent
through put
over a wide range of drive pressures.
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The valves 24 and 25 are located at the half round extremities of the cavity
and in close
proximity to the cavity. This proximity of the valves to the cavity thus
minimises voids
thereby giving optimum dry prime and compression ratio.
The pump arrangement is such that only low inertia needs to be overcome in
order to
drive the membrane. The valves are progressively closed and finally close
before full
exhaust or intake. This means that the last thing to occur as the membrane 14
reaches
its stable position is movement of the valves into a closed position or
opening is the
first thing to occur upon the membrane 14 moving from a stable position.
The invention as described herein is by way of example only and it will be
appreciated
by those skilled in the art that other embodiments incorporating the invention
are
possible.
