Flow stabilizer for a ventilation duct

A stabilizer for a ventilation duct includes a sensor, sensitive to a variable parameter such as temperature, which affects the flow of air in the duct. The sensor includes an opening in a return flow conduit communicating with a deformable chamber contained within a section of the duct. As the parameter changes, pressure at the opening changes thereby affecting the volume of the chamber and likewise the volume of the section of the duct in which the chamber is located.

BACKGROUND OF THE INVENTION 
This invention relates to an improvement in a flow stabilizer for a 
ventilation duct. 
Prior flow stabilizers, as exemplified by French Pat. No. 70 12 065, 
comprised a chamber consisting of a deformable bag, a seat supporting the 
chamber with a hole permitting air to enter or exit from the chamber, and 
means adapting the seat to the ventilation duct, so that the orifice is 
directed upstream. The respective dimensions of the chamber and the 
section of the duct were such that under the action of pressure 
differences existing upstream and downstream, the variation of volume of 
the chamber which resulted therefrom modified the section for the passage 
of air in the space made between the chamber and the duct. These devices 
had been designed to stabilize the air flow without amplifying its sudden 
fluctuations, and consequently without maintaining fluctuating operating 
conditions in the duct. 
Although the bag constituting the chamber was made of an elastic and 
flexible material, because of the loss of elasticity of this material due 
to its aging, this stabilizer, was only slightly durable. 
To eliminate this drawback, flow stabilizers were developed as shown in 
French Pat. No. 79 24 829, having elastic means associated with the bag 
chamber so that the elastic means was housed inside the chamber to provide 
its return to a minimum volume when the pressure difference between the 
ventilation duct areas located upstream and downstream from the chamber 
fell below a predetermined threshold. 
Thus, the bag could be formed by molding it in the shape corresponding to 
its maximum volume, which, with the absence of undercut, facilitated its 
removal from the mold, and its return to its minimum value was no longer 
dependent upon its own elasticity. Its life was therefore considerably 
increased. 
SUMMARY OF THE PRESENT INVENTION 
The object of this invention is to provide a stabilizer of the type 
described above which is sensitive to the measured values of a variable 
parameter and capable of operating when the pressures in the ventilation 
ducts are very slight, which is the case in air conditioning units. 
Accordingly, in the stabilizer of the present invention, the intake and 
outlet opening of the deformable chamber is connected by an auxiliary pipe 
to a pressure sensor associated with means for amplifying the effect of 
the dynamic pressure of the stream of air as well as with means sensitive 
to the variations of the parameter chosen, other than the pressure, and 
acting on the sensor to modify its action on the deformable chamber as a 
function of said variations of this parameter, at least when its value 
exceeds the limits of a predetermined range. 
Consequently, the flow controlled by this stabilizer varies as a function 
of the variations of the parameter chosen. 
According to a first embodiment of this stabilizer, the body of the device 
exhibits an auxiliary Venturi-shaped duct, constituting means for 
amplifying the effect of the dynamic pressure of the stream of air, whose 
intake and outlet are located, respectively, upstream and downstream from 
the deformable chamber. In the neck of the chamber, the auxiliary pipe 
emerges through an orifice constituting the pressure sensor, and a cavity 
is provided in the wall of the chamber upstream from the opening of said 
pipe. The cavity houses a valve movable crosswise to the duct, and 
includes a stem joined to a movement amplifying lever, itself joined to 
the means sensitive to the variations of the parameter chosen, and 
associated with elastic means, so as to control the retraction of the 
valve in its housing if the value of the parameter chosen exceeds a 
predetermined threshold and vice versa. 
If, for example, the parameter chosen is the rate of humidity in the air, 
the means sensitive to the variations of this rate comprise the hair of an 
hygrometer subjected to the action of the air that circulates in the duct, 
and a small rod articulated on the lever rests, by its free end, on the 
hair of the hygrometer so as to cause the lever to pivot in the direction 
corresponding to the output of the valve when the hair becomes taut 
because of the reduction of the rate of humidity. 
It is easily understood that the output of the valve resulting from the 
reduction of the rate of humidity in the air causes an increase of the 
pressure in the part of the main duct located upstream from this valve 
and, consequently, an inflation of the deformable chamber and a reduction 
of the stabilized flow. 
According to a variant embodiment of the invention, the pressure sensor 
comprises a radial opening made in one of the ends of a cylindrical tube 
mounted in the body of the stabilizer so that this end projects into a 
part of the main duct located upstream of or at, the deformable chamber. 
The inner chamber is connected, through an airtight connection, with the 
auxiliary pipe, and the means sensitive to the variations of the parameter 
chosen is designed to modify the position of the radial opening in the 
main duct as a function of the variations and thus to amplify the effect 
of the dynamic pressure on it of the stream of air circulating in the main 
duct. 
By modifying the position of the pressure sensor in the stream of air, the 
angle of incidence of the dynamic pressure of this stream of air on the 
operation of the stabilizer is modified. For example, the radial opening 
constituting the sensor can be oriented perpendicular to the flow of the 
stream of air and the modification of its position consists in a crosswise 
movement of the cylindrical tube in which said radial opening is disposed 
between two end positions, of which one corresponds to a maximum partial 
vacuum at the sensor and, consequently to a minimum volume of the chamber 
and a maximum air flow located at the deformable chamber, and the other of 
which corresponds to a minimum partial vacuum at the sensor and, 
consequently, to a maximum volume of the chamber and a minimum air flow 
located upstream from the deformable chamber. 
Thus, for the same air flow, inflation of the deformable chamber increases 
and the stabilized flow decreases when the sensor is moved upstream, i.e., 
is moved away from the deformable chamber. 
According to another particular embodiment of the stabilizer, the 
cylindrical tube is mounted in the body, so that the end including the 
radial opening constituting the pressure sensor is located at the 
deformable chamber, i.e., in the area of the smaller section of the main 
duct. Consequently, the greatest speed of the stream of air occurs at the 
sensor. The sensor is supported to pivot about its longitudinal axis and a 
control shaft extension, provided on the end opposite the end having the 
radial opening, is coupled to the means sensitive to the variations of the 
parameter chosen and associated with elastic means. The sensor is caused 
to pivot between a position in which said radial opening is oriented in 
the direction from which the stream of air circulating through the main 
duct comes (corresponding to maximum inflation of the deformable chamber) 
to a position in which the radial opening is oriented perpendicular to the 
direction of flow of the stream of air (corresponding to a maximum 
deflation of the deformable chamber) when the value of the parameter 
chosen increases. The airtight connection between the inner chamber of the 
revolving tube and the auxiliary pipe is provided by a revolving joint. 
It is easily seen that, when the radial opening constituting the pressure 
sensor is oriented perpendicular to the direction of flow of the stream of 
air, the inner chamber of the revolving tube, and consequently, the 
deformable chamber are subjected to a partial vacuum arising from flow of 
the stream of air tangentially to said radial opening. 
If, for example, the parameter chosen is the temperature, the means 
sensitive to its variations and the elastic means which are associated 
with them comprise a helical bimetallic strip one end of which being 
fastened to the body of the stabilizer and the other end being secured to 
the shaft extension that extends from one of the ends of the sensor.

DETAILED DESCRIPTION OF THE INVENTION 
The two embodiments illustrated in the drawings are stabilizers of known 
types comprising a body 2 that can be adapted to a ventilation duct not 
shown in the drawing and in which is housed at least a main duct 3, a 
chamber 4 comprising a deformable bag 5 located in main duct 3, a seat 6 
supporting the bag 5, with a hole made in small section 7 that allows the 
air to enter and exit from chamber 4 and recess or shoulder means that 
make it possible to adapt the seat 6 to body 2 of the apparatus. The 
respective dimensions of chamber 4 and crosswise sections of main duct 3 
are such that under the action of the pressure differences existing 
upstream and downstream from bag 5, the variations of volumes of chamber 4 
which results from it modify the section for passage of the air in space 
made between the wall of chamber 4 and the walls of main duct 3. 
A spring 8 held by seat 6 may be associated with bag 5 to return chamber 4 
normally to a position of minimum volume. 
This known stabilizer, therefore, has as its function the stabilization of 
air flow in the ventilation duct independently of the variations of the 
difference of pressures existing upstream and downstream from the 
apparatus. 
The object of this invention is to make possible an automatic adaptation of 
the adjustment of this stabilized flow as a function of the variations of 
a parameter other than pressure, and especially, under temperature or air 
humidity conditions over determined ranges of these parameters, even if 
the pressures brought into play are very slight, as is the case in air 
conditioning units. 
To effect this purpose, the intake and outlet opening 7 of chamber 4 is 
connected by an auxiliary pipe 9 to a pressure sensor associated with 
means sensitive to the variations of the parameter chosen and to act upon 
it to modify its action on chamber 4 as a function of the variations of 
this parameter, at least when its value exceeds the limits of a 
predetermined range, and to amplify the effect of the dynamic pressure of 
the stream of air on the pressure sensor. 
In the example illustrated in FIGS. 1 and 2, the parameter chosen is the 
hygrometry rate of the air circulating in the ventilation duct and the 
means sensitive to the variations of this parameter comprise hair 11a of 
the hygrometer 11 held by body 2 of the apparatus so that hair 11a is 
exposed to, and is licked by the air flow that circulates in the 
ventilation duct. For this purpose, the wall upstream from body 2 includes 
an opening 12 that allows the entrance of an air flow that licks hair 11a 
all along its length. 
In this example, body 2 exhibits an auxiliary Venturi-shaped conduit 13 
which comprises the means for amplifying the effect of the dynamic 
pressure of the stream of air on the pressure sensor. The intake and 
outlet of this auxiliary duct 13 are located, respectively, upstream and 
downstream from deformable chamber 4. Auxiliary pipe 9 connecting input 
and output opening 7 of chamber 4 to the pressure sensor connects with 
auxiliary duct 13 at its neck 13a at opening 14 that constitutes the 
pressure sensor. 
In the wall of auxiliary duct 13 downstream from neck 13a and, 
consequently, from opening 14 of auxiliary pipe 9, a cavity 15 is provided 
which houses a valve 16 movable crosswise to auxiliary conduit 13 between 
two positions; a first for retraction (represented by the solid lines in 
FIG. 2) and a second for total output (represented by dotted lines in the 
same figure). In the second position, the valve 16 almost totally 
obstructs auxiliary conduit 13. 
The valve 16 is carried by a rod 17 that slides axially in a bearing 18 and 
includes a free end connected to one of the ends of a lever 19. The lever 
19 is pivotably carried by a transverse horizontal shaft 21 supported on 
body 2 of the apparatus and is balanced by a counterweight 22. A small rod 
23 is connected at one of its ends to lever 19 at a point located between 
rod 17 and the connection shaft 21. The other end 23a of rod 23 has the 
shape of a fork and bears against hair 11a of hygrometer 11, perpendicular 
to the latter. A spiral spring 20 is mounted about shaft 21, and has one 
end connected to lever 19 and its other end connected to shaft 21. Spring 
20 normally biases forked end 23a of small rod 23 against hair 11a of 
hygrometer 11. 
Hair 11a of hygrometer 11 is normally made of polyamide, and the change of 
its length is dependent on the relative humidity of the air. Spring 20, 
therefore, provides the maintenance of tension of hair 11a. 
The operating principle of this stabilizer is as follows: 
Under ordinary conditions of use corresponding to relative humidities 
between 30 and 70%, the length of hair 11a is such that valve 16 assumes a 
position where it partially blocks auxiliary conduit 13. This position is 
an intermediate position between those solid, and dotted line positions 
represented in FIG. 2. 
When the relative humidity of the air decreases, the length of hair 11a 
decreases, which causes a downward movement of small rod 23 and, 
consequently, an amplified pivoted movement of the end of lever 19 
connected to rod 17 and a corresponding downward movement of valve 16 in 
the direction of its maximum blocking position. Therefore, valve 16 tends 
to obstruct auxiliary conduit 13 even more. When the relative humidity of 
the air increases, the movements of valve 16 and of the elements which 
control it are obviously reversed. 
The deformation of bag 5 depends on the pressures that are exerted on the 
outer faces of its walls and on the pressure imposed on its inside by 
pressure sensor 14 and auxiliary pipe 9. The difference between the 
pressure P.sub.2 that prevails downstream from the stabilizer and that of 
the pressure Pv imposed on the inside of bag 5 (i.e., Pv-P.sub.2) is equal 
to k (P.sub.1 -P.sub.2), a formula in which P.sub.1 is the pressure that 
prevails upstream from the stabilizer, and k coefficient dependent on the 
position of valve 16 with respect to auxiliary duct 13 and, consequently, 
on the relative humidity of the air. 
For relative humidity between 30 and 70%, valve 16 partially obstructs 
auxiliary duct 13, and Pv therefore takes a middle value between P.sub.1 
and P.sub.2, k being positive and less than 1. The value of k decreases 
when the relative humidity increases. 
The pressures to which the lateral walls and the posterior face of bag 5 
are subjected, from the outside, are approximately equal to P.sub.2 ; thus 
over the range of value between 30% and 70% of the rate of relative 
humidity of the air, the differences between the pressures exerted on the 
inside and the outside have a tendency to inflate bag 5. For a determined 
relative humidity between 30% and 70%, when the drive pressure of the air 
P.sub.1 -P.sub.2 increases, Pv-P.sub.2 increases, the bag is inflated and 
the passage for the air decreases so as to maintain the air flow at a 
value nearly independent of the drive pressure. 
The value of the flow thus stabilized depends on the value of k, and on the 
rate of relative humidity; the greater this value the greater the relative 
humidity. 
For very high relative humidities, for example 90%, (temporary conditions 
corresponding, for example, to the use of a shower or bath) valve 6 
totally retracts in its housing 15. The Venturi-shaped auxiliary duct 13 
is no longer disturbed by the presence of valve 16 and the static pressure 
at neck 13a and, consequently, of pressure sensor 14 decreases 
considerably to reach values lower than the pressure P.sub.2 that prevail 
downstream. Coefficient k is then negative, and the volume of bag 5 
decreases and becomes smaller than its volume at rest. The air flow in the 
ventilation duct is increased considerably, and is no longer stabilized. 
In this case, however, the desired goal is reached, since the operation of 
this stabilizer aims at very rapidly reestablishing the normal ambient 
conditions. 
In the embodiment of this stabilizer illustrated by FIGS. 3 and 4, the 
parameter chosen is the temperature. 
In FIGS. 3 and 4, the elements identical with those of the embodiment 
illustrated by FIGS. 1 and 2 are designated by the same references, and 
are not described again. 
In this second embodiment, a cylindrical tube 24 is mounted to pivot around 
its longitudinal axis in a bearing made in the body 2 of the apparatus, 
and one of its ends projects into the space made between the chamber 4 and 
the lateral wall of the main duct 3, i.e., into the area of the smallest 
section of the main duct 3 and of the greatest speed of the stream of air. 
The other end of tube 24 is extended by a shaft 25 located outside body 2. 
Tube 24, which is closed at both its ends by diametrical walls, exhibits at 
its end projecting into the main duct 3 a radial opening 26 that 
constitutes the pressure sensor and, in the vicinity of the other end, a 
radial opening 27 that communicates by a revolving joint 28 with the 
auxiliary pipe 9. Ring seals 29 provide the tightness between the tube 24, 
the body 2 of the apparatus and the revolving joint 28. A bimetallic strip 
31 is helically wound on the shaft 25 that extends the tube 24, one of the 
ends of this bimetallic strip 31 being fastened to the body 2 while its 
other end is fixed on the shaft 25. 
The flow stabilizer regulated as a function of the temperature is 
particularly intended for the removal of the gases burned by home gas 
furnaces. When the furnace is operating, the flow of evacuated fumes must 
increase, which involves a decrease in the volume of the deformable 
chamber 4 when the temperature increases. 
The operation of this stabilizer sensitive to the variations of temperature 
is, therefore, as follows: 
When the temperature is low, pressure valve opening 26 is directed toward 
the air flow that circulates in the ducting, i.e., in the main duct 3, as 
illustrated in FIG. 3. Pressure sensor 26, therefore, receives a maximum 
pressure that it transmits through tube 24, opening 27, and auxillary pipe 
9 to the inside of chamber 4. The volume of the chamber reaches its 
maximum possible value with a determined driving pressure P.sub.1 
-P.sub.2. The flow is stabilized at a low value when P.sub.1 -P.sub.2 
varies. 
When the temperature of the air rises, bimetallic strip 31 causes shaft 25 
and tube 24 to rotate, which tends to rotate orifice 26 out of the air 
flow, in such a way that the air intake is subjected to a lesser pressure. 
For a determined pressure P.sub.1 -P.sub.2, the volume of chamber 4 
decreases and the passage for the gases increases. The flow that goes 
through main duct 3 of the stabilizer is, therefore, stabilized at a 
higher value. At the limit, the stream of air tangentially licks opening 
26, creating a partial vacuum which forces bag 5 to be deflated, and thus 
sensor 26 amplifies the effect of the dynamic pressure of the stream of 
air on sensor 26. 
It goes without saying that the invention is not limited only to the 
embodiments of this stabilizer which have been described above, by way of 
nonlimiting example. On the contrary, it includes all the variant 
embodiments. Thus, for example, in the embodiment illustrated by FIGS. 1 
and 2, the stabilizer could be associated with means sensitive to 
temperature, while, inversely, in the embodiment illustrated by FIGS. 3 
and 4, it could be associated with means sensitive to the relative 
humidity of the air.