Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02249113 1998-10-02
85862-1
AIRFLOW RATE REGULATING DEVICE
Field of the invention
The present invention relates to the art of airflow regulation devices. In
particular, the invention finds applications in airflow rate control devices
that
may be typically used in enclosures to provide a source of suction to a
processing station and at the same time assist in maintaining the enclosure at
a negative pressure relative to an adjacent room. Such installations are
usually
found in pharmaceutical plants where it is essential to avoid chemical
substances being released outside a certain enclosure.
Background of the invention
In many applications, it is desirable to control the air pressure within a
space
such as in so called « clean rooms » used in laboratories, biotech,
biomedical,
hospital, cosmetic, food processing, research center, semiconductor
industries,
etc... For instance, pharmaceutical installations that produce medicinal
tablets
are required by regulation to confine the tablet manufacturing equipment
within
a closed space and provide an airfiltration system capable of establishing in
the
closed space negative air pressure in the space such that when an access door
is opened airborne particulate matter will have a tendency to remain in the
space.
Traditional air filtration systems have drawbacks. Perhaps, the most
acute one is the inability of the system to react rapidly enough to air
pressure
variations in the space (occurring when a door is opened) to stabilize the air
pressure to its nominal value. This slow response time is the result of the
strategy employed to regulate the air pressure. More particularly, prior art
air
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filtration systems rely on electric actuators to alter air flow in order to
provide the
pressure control function. Such electric actuators, are usually slow to react
which translates into a lengthy response time for the overall system.
Therefore there exists a need in the industry to provide novel system and
components that alleviate the disadvantages of prior art air filtration
systems.
ObLects and statement of the invention
It is thus an object of the invention to provide an improved airflow rate
regulating device that alleviates at least some of the drawbacks associated
with
prior art air filtration systems.
As embodied and broadly described herein, the invention provides an airflow
rate regulating device, comprising:
- a first and a second chambers;
- an air flow passageway between said first and second chambers
establishing a fluid communicative relationship between said
chambers.
- said first chamber including a main port for connection to a
source of vacuum, said main port permitting air to be drawn from
said first chamber under the effect of negative pressure
established by the source of vacuum;
- said second chamber including a first air inlet and a second air
inlet for admitting air to said second chamber;
- said first air inlet including a first airflow rate regulation valve to
meter a rate at which air passes through said first inlet, said
airflow rate regulation valve including a movable member
extending across a flow of air though said first inlet and capable
to acquire a plurality of positions corresponding to different air
flow rates through said first inlet;
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- a second air flow regulation valve in said air flow passageway to
meter a rate at which air passes through said air flow
passageway, said airflow rate regulation valve including a
movable member extending across a flow of air though said air
flow passageway and capable to acquire a plurality of positions
corresponding to different air flow rates through air flow
passageway.
Other objects and features of the invention will become apparent by reference
to the following description and the drawings.
Brief description of the drawin4s
A detailed description of the preferred embodiments of the present invention
is
provided herein below, by way of example only, with reference to the
accompanying drawings, in which:
Figure 1 is a perspective view of a cabinet shown in dotted lines in which
the airflow rate regulating device according to a preferred embodiment of the
invention is mounted;
Figure 2 is an exploded perspective view of the device depicted in Figure
1;
Figure 2a is an enlarged perspective view of the movable valve member
of an airflow rate regulation valve;
Figure 3 is a perspective view illustrating the cabinet in which is mounted
the airflow rate regulating device, illustrating flexible hoses connecting the
airflow rate regulating device to processing stations;
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Figure 4 is a perspective view of the airflow rate regulating device
according to the invention, some components being cut-away to illustrate
internal parts;
Figure 4a is a cross-sectional view of the airflow rate regulating device
shown in Figure 4;
Figure 5 is a perspective view of a second embodiment of the airflow rate
regulating device according to the invention;
Figure 6 is a block diagram of an air filtration system utilizing the air flow
regulating device according to the second embodiment installed in a controlled
room;
Figure 7 is a perspective view of an airflow rate regulating device in
accordance with a third embodiment;
Figure 8 is a perspective view of a variant of the third embodiment of the
airflow rate regulating device according to the invention;
Figure 9 is a schematical view of the airflow rate regulating device in
accordance with the third embodiment of the invention installed in a
controlled
room.
In the drawings, preferred embodiments of the invention are illustrated by way
of examples. It is to be expressly understood that the description and
drawings
are only for the purpose of illustration and are an aid for understanding.
They
are not intended to be a definition of the limits of the invention.
Detailed description of preferred embodiments
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Figures 1 and 2 of the drawings illustrate the airflow rate regulating
device constructed in accordance with the preferred embodiment of the
invention. The airflow rate regulating device 35 is mounted in a suitable
cabinet
88 and it is connected to a vacuum source at central inlet 22 of the cabinet
88
through elbow 28 and conduit 30. Typically, the airflow rate regulating device
35 is integrated in an air filtration system and the vacuum source is a fan
unit
or a suitable pump designed to transport air through the filtration system. A
negative pressure is established at the main port 80 of the airflow rate
regulating device 35 by the vacuum source. A sliding gate valve 24 located
immediately next to the central inlet 22 allows an operator to set the initial
vacuum pressure at the main port 80 of the airflow rate regulating device 35
by
adjusting the opening of the sliding valve 24.
Fig.3 illustrates a typical unit installed in a controlled room. The flexible
hoses
50 are coupled to outer part of service ports 40 of the unit and are routed to
a
source of contaminants or multiple sources of contaminants of a processing
station 55. The contaminants produced by the processing station 55 are drawn
up and collected by the vacuum pressure created at the end of the flexible
hoses 50. As can be seen in fig. 1 and 2 , the airflow rate regulating device
35
draws air through two sources. The first source being through air inlet 74
which
is connected to the service ports 40 and the second source being through air
inlet 72 located on the side of the airflow rate regulating device 35 and
connected to the ambient room air inlet 52 of the cabinet 88.
Referring to fig.2 and 2a, and more specifically to fig.4 and 4a, the airflow
rate
regulating device 35 has a casing divided into two chambers 201 and 202
separated by a wall having an passageway 79 through which air flows from
chamber 202 to chamber 201. The first chamber 201 transports the air flow
passing through the airflow rate regulating device 35 and features an airflow
rate regulation valve 75 comprising a movable member 77 extending across the
flow of air passing through the passageway 79, that can be adjusted using
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counterweight 37. The counterweight 37 allows adjustment of the air flow i.e.
the actual volume of air per unit of time going through the airflow rate
regulating
device 35.
The second chamber 202 regulates the vacuum pressure at the service ports
40. The second chamber 202 features an airflow rate regulation valve 60
comprising a movable member 61 extending across the flow of air passing
through the air inlet 72, that can be adjusted using the counterweights 38.
The
adjustment of the counterweight 38 biases the movable member and effectively
regulates the amount of air coming from air inlet 72 and air inlet 74 so that
a
constant vacuum level can be maintained at the service ports 40.
The airflow rate regulating valve 60 is an assembly comprising a movable
member 61 in the form of a semi-spherical damper adjustably mounted on an
inverted U-shaped frame 62 which has two grooved apertures 63 to adjustably
fasten the movable member 61 to the U-shaped frame 62 . The frame 62 is
mounted on lever 45 which acts as a mechanical biasing member for biasing
the movable member 61 towards a certain position. Lever 45 passes through
the upper portion of frame 62. Lever 45 also passes through the case of the
airflow rate regulating device 35 and is held in place by two bushing 65
installed
in the apertures 66 of the airflow rate regulating device 35. Lever 45
preferably
features a flattened area 67on which the two fasteners 68 can lock lever 45
onto frame 62. Once the lever 45 and the frame 62 are locked together, final
adjustment of the position of the movable member 61 in relation to frame 62
can
be made by positioning the movable member 61 in seat 70 of the air inlet 72 in
such a way that the movable member 61 embraces the entire contour of the
seat 70, and then tightening the two fasteners 68 which hold the movable
member 61 onto frame 62. The seat 70 of air inlet 72 is made of a softer
material than the movable member 61, preferably a plastic or a rubber, and the
inner contour of seat 70 is bevel shaped to mate semi-spherical body of the
movable member 61. The airflow rate regulation valve 60 moves like a
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pendulum rotating about the axis defined by the lever 45. The lever 45
protrudes outside the airflow rate regulating device 35 and is shaped like an
"L".
On the outside portion of lever 45 is mounted the counterweight 38 which can
slide on the shaft of lever 45 to adjust the amount of torque it generates on
the
movable member 61. The amount of torque determines the level of bias. The
airflow rate regulation valve 60 effectively controls the amount of air drawn
from
air inlet 72 in response to pressure variations at the service ports 40.
The first chamber 201 also comprises an airflow rate regulation valve 75
constructed and assembled in same manner as described above for the airflow
rate regulation valve 60 but with one noticeable difference in the design of
the
body of the movable member 77. The body of the movable member 77 has a
circular aperture 76 in its center. Since chamber 201 regulates the air flow
passing through the airflow rate regulating device 35, a minimum quantity of
air
must go through the airflow rate regulation valve 75 and the circular aperture
76 provides for that minimum amount of airflow. Even with the movable
member 77 fully seated against seat 78 of the passageway 79, a minimum
quantity of air is able to pass from second chamber 202 to first chamber 201
by
way of this circular aperture 76. Again, the airflow rate regulation valve 75
moves like a pendulum rotating about the axis defined by the lever 44 and
provides a counterweight 37 which can slide on the shaft of lever 44 to adjust
the amount of torque it generates on the movable member 77.
Referring to fig.1, 4 and 4a; in operation, the airflow rate regulating device
35
draws air and contaminants from the flexible hoses 50 at a set vacuum pressure
and a certain quantity of air is also drawn from the ambient room air inlet 52
at
room pressure. When a pressure disturbance occurs, whether in the controlled
room from a door opening orwhen one ofthe flexible hoses 50 is disconnected,
the airflow rate regulation valve 60 which regulates the amount of air drawn
from the two air inlets (72 and 74) reacts. The counterweight 38 setting
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provided for a precise pressure differential at the service ports 40. Now that
the
pressure has risen in the controlled room and therefore at the processing
machine end of the flexible hoses 50, the pressure differential established at
the
service ports 40 in steady state thereby decreases. The torque exerted by
counterweight 38 on the movable member 61 being a constant, forces the
movable member 61 down so as to restrict the airflow coming from the first air
inlet 72 of the ambient room air inlet 52. By reducing the amount of air drawn
from first air inlet 72, more air must be drawn from the flexible hoses 50
(air inlet
74) thereby re-establishing the pressure differential previously set at the
service
ports 40. The advantage of this mechanism is that its response time is nearly
zero; the torque generated by counterweight 38 is set and balanced against the
pressure differential established in steady state at the service ports 40 so
that
if a pressure variations occurs in the controlled room, the airflow rate
regulation
valve 60 will open or close the first air inlet 72 in order to keep these two
forces
(torque of the counterweight and pressure differential pull in the opposite
direction) in equilibrium.
To maintain a constant air flow, the airflow rate regulation valve 75 is set
using
counterweight 37. Again if a pressure disturbance occurs in the controlled
room
from a door opening, the airflow rate regulation valve 75 will react by
restricting
the passageway 79. The setting of counterweight 37 uses the same two forces
described above for counterweight 38 so that when pressure rises in the
controlled room as in this example, the equilibrium established in steady
state
is disturbed and the counterweight 37 forces the movable member 77 down so
as to restrict or close the passageway 79 in order to reestablish the
equilibrium
between the pressure differential at main port 80 and the torque of
counterweight 37. Since the airflow rate regulation valve 75 has a circular
aperture 76 in its center and is located downstream from the airflow rate
regulation valve 60, its modulations are usually smaller than the modulations
of
the airflow rate regulation valve 60.
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The static pressure maintenance within the controlled room may also be
assisted by the airflow rate regulating device 35. Because of the constant
exhausted air flow it generates, the airflow rate regulating device 35 can and
does assist in maintaining the pressure differential between the controlled
room
and the outside of the room. The setting point of the airflow rate regulating
device 35 is such, that when the worst case condition occurs , i.e. when doors
of the process room are open, this room will remain at a point below the
static
pressure outside of the controlled space to ensure that such contaminants will
not migrate outside of the controlled space. In case of complete failure of
the
central ventilation system, the airflow rate regulating device 35 is capable
of
maintaining, at least partially, the lower static pressure of the controlled
room.
Also, an interesting feature of the airflow rate regulating device 35 is the
fact
that, with its capacity to maintain constant vacuum pressure at the inlet of
the
flexible hoses 50, special dust catch pans 85 as shown in fig. 3 can be
installed
at the collecting points of the processing station 55 without disturbing the
process conditions thereby allowing an optimum removal of all contaminants
directly at the sources.
As an added feature, the casing 88 as well as the conduits leading to the
airflow
rate regulating device 35 are lined with an acoustic material which partially
absorbs and dampens the sound created by the air flow though the airflow rate
regulation device 35. The device so equipped is very quiet and does not expose
people working next to it to high pitch sound. Since the airflow rate
regulating
device 35 does not have a motor and rely on a vacuum source located
downstream, it is a very quiet device.
The present invention may be assembled and constructed as a complete
surface model as represented in fig. 7 and 8 , as a regular unit 10 as
represented in fig. 1, 2 and 3 or as a dissimulated model as represented in
fig.
5 and 6. The dissimulated variant 100 of the present invention is reduced to
the
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airflow rate regulating device 35 with again two air inlets 72 and 74. The
second
air inlet 74 is located on the side of the dissimulated variant 100 instead of
above. A flexible conduit 104 is coupled to the second air inlet 74 and
collects
air and contaminants from a processing station. The first air inlet 72 draws
its
air from the controlled room itself through connection 105. A sliding gate
valve
101 is provided to adjust the initial vacuum pressure. The dissimulated
variant
100 of the present invention can be installed behind the walls of the
controlled
room as shown in flg. 6. The vacuum pressure is created by the vacuum
source 15 located downstream of the exhaust conduit 16 and a dust collector
17 is inserted into the exhaust conduit 16 between the vacuum pump 15 and
the dissimulated variant 100 to filter the contaminants collected from the
processing station.
A complete surface model 120 is illustrated in fig. 7, 8 and 9. It features
the
same basic characteristics as the regular unit 10 depicted in fig. 1 to 3 but
it has
been modified to accommodate the filtering unit 122. Contaminants are
collected through flexible hoses routed to the processing station in the same
manner as the regular unit; the airflow rate regulating device 35 controls air
flow
and vacuum pressure at the service ports 40 but instead of being evacuated
immediately, air and contaminants are evacuated through a side main port 80
of the airflow rate regulating device 35 linked to a conduit 124 which leads
to
a filtering unit 122 where contaminants are removed from the airflow and
trapped. The contaminants fall in a bag (not shown) positioned at the bottom
of the filtering unit 122 which can be removed through the access door 126.
Clean air exits the filtering unit 122 and passes through conduit 128 which
features a sliding gate valve 132 and leads to a vacuum source 140.
Adjustment of the initial vacuum pressure is achieved by opening or closing
the
sliding valve 132.
This complete surface model 120 features its own power source 135. The
power source 135 is preferably an electric motor coupled to a fan blower, a
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compressed air turbine or a compressed air venturi. Air from conduit 128
passing through sliding valve 132 is drawn by the fan 140 and evacuated
outside the complete surface model 120 through the silencer air outlet 142.
The
complete surface model 120 has the advantage of being completely self-
sufficient. As shown in fig. 9, the clean exhaust air is evacuated at a higher
pressure than the previously collected air and is preferably delivered in the
adjacent corridor 150 or the next room to assist in maintaining the necessary
pressure differential between the outside of the controlled room and the
controlled room.
Figure 8 represent a variant of the complete surface model 120. The filtering
unit 122 uses a compressed air filtering cartridge 144 as a means to collect
contaminants from the airflow rate regulating device 35. As a variant of the
vacuum source, this particular model features a compressed air system. The
initial vacuum pressure is derived from compressed air introduced into the
system at air inlet pipe145 where it is split at intersection 146. A first
portion of
compressed air is routed directly into exhaust conduit 147 and through the
silencer 142. A second portion of compressed air is routed into the compressed
air filtering cartridge 144. The necessary vacuum to run the airflow rate
regulating device 35 is established by the compressed air evacuated directly
into exhaust conduit 147. As the compressed air rapidly exits conduit 147, it
creates a vacuum pressure behind this point that is sufficient to act as a
proper
vacuum source to run the airflow rate regulating device 35 . This arrangement
eliminates the use of a power source in the complete surface model 120. Of
course, this compressed air arrangement can be used in any variants of the
airflow rate regulating device 35, may it be the complete surface models 120,
the regular unit 10 or the dissimulated model 100. Each may be modified to
function with a compressed air arrangement.
The exhausted air passing through the airflow rate regulating device 35, which
is a mixture of contaminated source captured air from the process and ambient
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air from the controlled room, can be evacuated through a central ventilation
system after filtration, returned into the central ventilation system after
filtration,
or re-circulated, after local filtration, into adjacent rooms or corridors to
help in
the pressurization of these rooms or corridors .
The above description of preferred embodiments should not be interpreted in
a limiting manner since other variations, modifications and refinements are
possible within the spirit and scope of the present invention. The scope of
the
invention is defined in the appended claims and their equivalents.
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