Feed chute for fiber tufts

A flap is disposed across the opening between an expansion chamber and an exhaust air duct to control the delivery of fiber tuft-laden air into a feed chute or chamber. The flap has two wings which pivot about a common pivot axis whereby as one wing increases the flow cross section from the expansion chamber, the other wing reduces the flow cross section. A pressure difference produces forces on both wings simultaneously.

The invention relates to a feed chute (for instance at a card) or a similar 
feed chamber (for instance in a blender (mixer), for instance according to 
European Patent Application 383246) which during operation is supplied 
with fiber tufts from a pneumatic tuft conveying system. The chute or feed 
chamber, as the case may be, separates the tufts from a conveying air 
stream, which air stream is then exhausted through an air duct. The 
pressure conditions in the chute, or feed chamber, change as a function of 
the filling level and this fact is preferably utilized to influence the 
supply of the tufts from the conveying system to the chute or feed 
chamber. Known art 
A feed chute for a card which operates according to the previously 
described method is known from U.S. Pat. No. 4,878,784. A blender (mixer) 
which is provided with a similar chute is disclosed in European Patent 
Application 383246 and a suitable feed chamber is disclosed in European 
Patent Application 563700. The function for discharging a pneumatic tuft 
conveying flow from the feed duct into a feed chamber of that type depends 
on the momentary effective relation between the pressure in the feed 
chamber and the pressure in the tuft conveying duct at the entrance of the 
chute. According to U.S. Pat. No. 4,878,784 as well as according to 
European Patent Application 563700 these relations depend on the momentary 
filling level in the feed chamber. 
In both cases, there is also a valve mounted between the feed chamber and 
the exhaust air duct. The valve according to U.S. Pat. No. 4,878,784 is 
closed through positive action, if there is no need for material from the 
feed chute. Thus, the discharge of conveying air from the feed duct into 
the chute is stopped. Otherwise, the valve is open due to the pressure 
difference between the intake and discharge and the valve itself 
influences this difference in dependence of the selected arrangement 
(according to FIG. 5, FIG. 6 respectively of U.S. Pat. No. 4,878,784 
patent). The influence of the valve can be chosen through the adjustment 
of a force exerting means consisting of a lever and a shiftable weight, 
within given limits. 
The valve according to European Patent Application 563700 is not closed 
through positive action and as long as a pressure difference is maintained 
between both sides of the valve, at least a "remnant flow" passes through 
the valve. If this remnant flow develops sufficient force, the valve opens 
itself; if the remnant flow drops below a predetermined force, the valve 
closes itself again. In this case too the functional behavior of a valve 
can be influenced by way of an adjusting means, which comprises a lever 
with a shiftable weight attached to the lever. 
These systems generally perfom excellently and have proven to be useful in 
practice during the past years. However, the ability of these systems to 
adjust themselves to the pressure changes proved to be insufficient in 
practice and are repeatedly the subject of complaints. The reasons for 
them are explained closely hereafter in connection with the figures of the 
drawings, so that at this point no further details need to be disclosed. 
From the above mentioned facts it becomes clear, however, that an object 
of the invention is to provide a valve for the above mentioned purpose, 
which at least, over a sufficient range is self-adjusting in relation to 
pressure changes. 
The invention 
The invention comprises a feed chamber for fiber material, which during 
operation is supplied with fiber tufts from a pneumatic tuft conveying 
system, which separates the tufts from the conveying air stream and which 
exhausts the air through a valve. The pressure conditions in the feed 
chamber change as a function of the filling level and are utilized to 
influence the delivery of the tuft-laden air to the feed chamber from the 
conveying system. The valve comprises a flap, which, by its weight, 
remains in a predetermined resting position if no air flows through the 
valve. Also, while in the resting position, at least one opening remains 
which allows a flow through the valve. This flow produces forces on the 
flap, so that, at given flow conditions, the flap is forced out of its 
resting position, thereby changing the flow section of said opening. 
The opening can be one of two openings of a kind, which can be influenced 
by the position of the flap in such a way, that at least within the given 
range of movement, an enlargement of the flow section of one opening is 
accompanied by the reduction of the flow section of the other opening. 
Adjustment means (such as lever and shifting weights) are not necessary. 
The flap can be movably supported on a holder, so that the position of the 
flap, in relation to the holder depends on the difference of pressure 
between one side and the other side of the flap. The flap can be supported 
rotatably and can comprise two wings, whereby an air stream passing the 
flap will have to produce forces at least on one of the two wings. 
One of the wings can be arranged in such a way that it influences the flow 
section of a first flow opening. The other wing can be arranged in such a 
way that it influences the flow section of a second flow opening. The 
arrangement can be furnished in such a way that the second flow opening is 
closed if the first flow opening is opened to its maximum flow section 
and/or the first flow opening is closed if the second flow opening is 
opened to its maximum flow section. In this context the "flow section" 
represents the determining factor for the flow resistance of the opening. 
The wings can be of flat shape. They preferably extend slantedly from the 
holder away in the direction of flow.

FIGS. 1 and 2 show the known state of the art. During operation, the feed 
chute 20 according to FIG. 1 is fed with fiber tufts from preceding 
machines of a blow room line via a pneumatic feed duct 22 (also called 
conveying duct). From this duct 22, tufts are fed into the feed chute 20, 
in that part of the conveying air stream is led downwards into a feed 
chamber 24. A wall 26 of this chamber 24 is perforated for air passage, so 
that the conveying air can enter an expansion chamber 28 and from where 
the air can discharge into an exhaust air duct 30. The tufts themselves 
cannot pass through the perforations of the wall 26 and form a (not shown) 
cotton batt in the feed chamber 24 above a feed roller pair 32. 
The feed rollers 32 can be driven by a motor 34 to feed material taken off 
from the batt, from the chamber 24, to an opening roller 38 driven by 
means of a motor 36. Accordingly, the chamber 24 thus serves as a feed 
chute storing a certain amount of material. 
The material conveyed by the feed rollers 32 and the opening rollers 38 
either drops as small tufts or as single fibers into a so called feeding 
silo 40, where it builds up a column of fibers or tufts (not shown) above 
a pair of delivery rollers 42. By a drawing off unit 44, the material from 
the lower end of this column can be supplied to a feed roller 46 of a not 
further shown card. Although the feed chute 20 is designed in particular 
for the feeding of the card, it is principally possible to use a similar 
chute for feeding the fiber material to other machines of a blowing room 
machine line. The supply from the drawing-off unit 44 depends on the 
demand of the machines that follow, which demand can periodically vary to 
a great extent. Despite this, it is important to maintain a constant 
height and compression of the material column as far as possible. 
A device for sensing the height of the column in the feed silo 40 is 
provided and comprises in the shown example a lower light barrier 50 and 
an upper light barrier 52. The function of these light barriers in 
connection with the motor 34 is well known and has been described in the 
literature; thus a further description is not necessary in this 
disclosure. 
The expansion chamber 28 comprises an arc shaped duct part followed by a 
funnel shaped part 5, provided with a throttle wing 6 (or flap) at its end 
which is followed by the exhaust air duct 30. The throttle wing 6 is 
swivably supported on a rotatable axis 8, the axis 8 being held 
stationary. 
At the end of the throttle wing 6 opposite to the axis, the throttle wing 
is furnished with a bulge 15, which, as indicated in FIGS. 1 and 2, in its 
resting position rests against a stop 7. The bulge 15 is provided with a 
groove (not shown), which leaves an opening between the bulge 15 and the 
stop 7 when the bulge 15 is resting on the stop 7, through which groove a 
tolerable, substantially predetermined quantity of air can flow. It is 
also possible to provide a bulge similar to the bulge 15 on the stop 7 
furnished with an opening in between similar to the above mentioned groove 
for the passage of a quantity of air. 
In addition, the rotatable axis 8 is provided with a weight lever 9 outside 
of the air duct consisting of the funnel shaped part 5 and the exhaust air 
duct 30. With regard to its swinging position, the lever 9 can be adjusted 
according to the arrows 12 indicating the swinging direction and it can be 
fixed in a given position. On the weight lever 9, furthermore, a shiftable 
weight 10 is provided, which can be shifted in the directions 11, 
indicated by the arrow, on the weight arm 9 and fixed in a predetermined 
position. 
The weight of the throttle wing 6 and the weight of the weight lever 9 as 
well as the shiftable weight 10, in combination with the position of said 
shiftable weight 10 on the weight lever 9, is chosen in such a way in 
that, when the throttle wing 6 is open, a nearly unstable balance is 
provided between the throttle wing 6 and the weight lever 9 together with 
the shiftable weight 10. 
Only little excess of pressure head is required to keep the throttle wing 6 
open. In spite of this the wing closes as soon as the air flow drops below 
a predetermined lower limit. 
FIG. 3 shows a change of the pressure P (ordinate) in the feed chamber 24 
with the time (abscissa), whereby it is assumed, that for the exhaust air 
wing according to FIG. 1, an upper limit pressure head value P2 and a 
lower limit pressure head value P1 have been defined. At the lower limit 
pressure head value P1 in the feed chamber 24, the wing should rest on the 
stop and at the upper limit pressure head value P2 in the feed chamber 24, 
the wing should be completely opened. The upper limit pressure head value 
P2 should correspond with the filling level with the state "feed chamber 
full", so that at that pressure level in the feed chamber no further fiber 
tufts (or only very few respectively) are to be delivered from the 
conveying system into the feed chute. The lower limit pressure head value 
P1 should correspond with the filling level state "minimal", so that at 
this pressure head fiber tufts are delivered at the maximum possible 
feeding rate. 
It is understood, however, that these pressure levels not only depend on 
the filling level of the feed chamber, but also on the pressure level in 
the feeding chute (at the chute entrance). This level represents a 
"reference value" which influences the pressure head in the feed chamber 
during the state "feed chamber full" as well as during the minimally 
allowed filling level. For relevant changes in pressure at the chute 
entrance, the position of the weight 9 along the lever 10 can be shifted, 
whereby for instance an upwards shifting of the two values P2, P1 
respectively results, in order to accomplish a corresponding shifting of 
the reference value. This adjusting device has to be used at least during 
assembly and when starting operation, in order to set the complete 
installation. The procedure, however, is difficult and the device does not 
suffice for practical application when a new setting up is to be carried 
out during normal operation, as will be explained further hereafter 
according to the FIGS. 4 to 6. 
The example according to FIG. 4 shows an installation that comprises a so 
called "line" of altogether eight cards 120. Above these cards runs a 
common feed duct 122. In the example, the cards are arranged in two rows, 
and thus the feed chute is U-shaped, which arrangement, however, is not 
relevant for this invention. At each end of the conveying duct 122 a fan 
124, 126, respectively, is connected that supplies conveying air. Each fan 
124, 126, respectively, has a feeding machine 128, 130, respectively, 
arranged to it to deliver fiber tufts. 
Each card 120 is provided with a respective feed chute 20, which receives 
tufts from the duct 122 and which delivers these tufts in the form of 
cotton to the corresponding card 120. The card arrangement shown in FIG. 4 
can be separated into two so called "lines", thereby using a suitable 
separating means. Such separating means are disclosed in European patent 
application No. 175056. After respective adjustment of the separating 
means, the installation can be put into operation in that one card line is 
delivered with tufts from the feed machine 128 and the other card line is 
delivered with fibers from the feed machine 130, whereby the number of 
cards per line can be suited to the production conditions of the spinning 
mill. 
Each line gives a certain flow resistance for the respective fan 124, 126 
respectively, which is expressed as a definable static pressure on a 
measuring device M in the duct 122 between the fan 124, 126 respectively 
and the first card of the line. If now the separating means is to be newly 
adjusted, then each newly defined line will give different flow resistance 
values for the respective fan 124, 126 respectively (higher or lower), 
which is expressed by a correspondingly change of static pressure on the 
measuring device M. 
FIG. 5 schematically shows the characteristic curve of a fan 124 or 126. 
For a predetermined operating speed n of the fan 124, 126 respectively, 
the static pressure P at the discharge side of the fan is connected (in 
connection) with the characteristic curve of the fan with the conveyed 
quantity of air Q. At a higher flow resistance of the installation (higher 
static pressure at the measuring device M) the fan conveys a relatively 
low quantity of air, for instance according to operating point A. At 
unchanged speed n, but a considerably reduced resistance (static pressure) 
the fan will convey a considerably higher quantity of air, for instance 
according to operating point X. 
This functional behavior of the fan can be adjusted to the conditions in 
the line, since a larger number of cards in the line results in a reduced 
flow resistance (static pressure) but, at the same time, requires an 
increased quantity of air. Therefore, it is not necessarily compulsory to 
carry out the required adjustment of the air quantity by a corresponding 
shifting of the characteristic curve of the fan (for instance for an 
increase of the air quantity, by a corresponding increase of the speeds of 
the fan from n to N, as indicated in FIG. 5 with a dotted line). The 
"definition" of the line connected (in connection) with the fan (that is 
of the "configuration the installation") determines without further action 
the static pressure at the exit of the fan and thus the quantity of air 
conveyed by the fan. 
An installation according to FIGS. 4 and 5 has a further advantage namely 
it can also adjust itself to the momentary operating conditions in the 
line, under the condition that a distinctive change of the operating 
conditions (for instance the breakdown of a card) leads to a corresponding 
change of the flow resistance (static pressure) within the system. This is 
the case within a system with feed chutes according to FIG. 1, since the 
breakdown of a card causes a throttling of the discharge of the conveying 
air from the feed duct 22 into the exhaust air system 30 and thus 
increases the flow resistance (static pressure) within the feeding system. 
This behavior can be utilized according to European Patent Application 
303023 in order to allow control of the tuft feed. 
The fan is thus self-adjusting, but the chutes connected to it are not. 
This poses a considerable problem in practice, as will be explained 
hereafter according to FIG. 6. 
FIG. 6 schematically shows the conditions in the upper part of a feed chute 
20. The shaded area 60 indicates a buildup of a column of tufts, which 
fills the feed chamber 24 about half way, whereby at this filling level 
tufts 62 should be continuously supplied from the feed duct. The uppermost 
space 64 of the feed chamber 24 assumes a static pressure of P1', which is 
mainly determined by the pressure in the feed duct. At the downstream side 
of the schematically indicated valve V, the exhaust duct 30 assumes a 
static pressure P3', which is mainly determined by the capacity of the 
exhaust system. The expansion chamber 28 assumes a static pressure of P2'. 
If the valve V is fully closed (which for instance in a system of the 
previously mentioned U.S. Pat. No. 4,878,784 can be forced by means of a 
control device), the pressure P2' increases to a value which approaches 
the value of pressure P1'. Thus, the delivery of tufts into the feed 
chamber 24 is effectively stopped since a discharge of a conveying air 
flow from the feed chamber 24 does practically not take place anymore. 
If now with an open valve V, the column of tufts in the feed chamber 24 
increases to the upper rim of the wall 26, a considerable drop of pressure 
develops between the space 64 and the chamber 28, so that P2' lies 
distinctly below P1'. This condition prevails while the valve V is being 
closed (the wing 6) in a system according to FIG. 1, whereby in this case 
the previously mentioned minimum quantity of air can still flow through 
the groove in the bulge 15. The pressure drop P1'-P2' is, however, 
determined by the design of the feed chamber 24. The pressure P2' at the 
state "feed chamber full" thus depends on the momentary value of the 
pressure P1'. 
As, however, has been explained with FIGS. 4 and 5, the value P1' basically 
changes in dependence of the chosen configuration of the installation. 
Furthermore there is also a certain influence from the momentary 
conditions of the other chutes that are fed by the same fan. This is 
illustrated in FIG. 7, wherein once again the characteristic curve of the 
fan is shown, this time however, with three characteristic curves I, II, 
III respectively, of the installation, in order to define three operating 
points AP1, APII, APIII respectively of the fan. Point AP1 corresponds 
with an installation condition, whereby all the chutes connected to this 
fan are empty. Point APII corresponds with a condition resembling an 
unchanged configuration of the installation, whereby all the chutes are 
full. Point APIII corresponds with a condition at which once again all the 
chutes are full, this time, however, with a changed configuration with 
additional feeding chutes arranged to the fan (this means a condition with 
an upward shifting of the "reference value"). 
In an installation with feed chutes according to FIG. 1 changes of 
configuration should be carried out with the manual readjustment of the 
weight 10 on lever 9 for each feed chute. This readjustment operation, 
however, turns out to be a rather delicate procedure, because the feed 
chutes react as "individuals" to a shifting of the weight, rather than 
according to a predetermined pattern. In practice therefore, readjustments 
are often neglected. Where these readjustments are carried out, the 
various feed chutes sometimes, in the end, turn out to show different 
basic settings. 
According to the present invention each flap should autonomously assume its 
own basic position, which is in agreement with the prevailing "reference 
value" of the pressure in the feed chute. This aim is reached by an 
embodiment according to FIGS. 8 and 9. For elements that already 
correspond with these elements described in the arrangement according to 
FIG. 1, the same reference numbers are used in the FIGS. 8 and 9. These 
are--the feed chamber 24 of the feed chute, the perforated wall 26 for the 
air passage, the expansion chamber 28, and the exhaust air duct 30. A 
valve assembly separates the duct 30 from chamber 28 and is constructed of 
a wall or support frame 70 secured to a wall (not shown) provided with an 
opening 72, which allows the flow of air from the chamber 28 into the duct 
30 as well as a flap 74 rotatable mounted in the frame 70 to influence the 
flow of air through the opening 72. 
The flap 74 comprises one single piece of plate with two wings 76, 78 
respectively, bent in relation to each other. The flap 74 is rotatably 
mounted on a horizontally rotatable axis 80 (e.g., defined by an axle) 
between the wings 76,78 such that the axis 80 divides the opening 72 into 
an upper part 72A and a lower part 72B. 
As can be seen in the example according to FIG. 10, the rectangular wings 
76, 78 are of different widths B1, B2 and the length L1 (in direction away 
from the axis 80) of the wing 78 is considerably shorter than the 
corresponding length L2 of the wing 76. The thickness of the material is 
the same for both wings so that the weight of the lower wing 76 is higher. 
The flap 74 is free-rotatably mounted to take on the illustrated position 
of FIG. 8, if no air flow prevails. The flap 74 is preferably made of a 
lightweight material with the dimensions of the wings suited according to 
the desired function of the flap (characteristic curve) as will be 
disclosed hereafter. 
In the position of FIG. 8, the opening 72A presents its greatest possible 
flow section in relation to the wall 70. It is not necessary to choose the 
shown position as the basic setting of the flap, but it is assumed here 
for the sake of simplicity. 
The position of the flap according to FIG. 8 is considered as the state 
"full" and the position according to FIG. 9 as the state "empty". These 
positions correspond with a full state and a empty state, respectively, of 
the chamber 24. At full state, the wing 76 rests on the wall 70, so that 
practically no flow is possible through the partial opening 72B. Between 
the wing 78 and the wall 70, however, a gap S remains open. This gap 
corresponds with the "minimum rate of flow opening" according to European 
Patent Application 563700. At the empty state, the upper wing 78 rests on 
or is close to the wall 70 so that the flow passage through the partial 
opening 72A is interrupted. The wing 76 however is now far away from the 
wall 70 so that the maximum flow through the partial opening 72B is 
possible. 
From its position according to FIG. 8, the flap 74 swings to the position 
according to FIG. 9 through a turning movement in a clockwise direction 
(according to these figures). The corresponding moment of rotation is 
produced by the air flow at the flap and has to overcome the effect of the 
weight of the flap. If the air flow declines, the opening moment of 
rotation decreases accordingly, and the flap 74 falls back into the 
position according to FIG. 8. The flap 74 can adjust itself to a variation 
in the air flow conditions within the chamber 28, since the previously 
mentioned air flows cause forces on the wings 76,78 and because these 
wings can be shaped to such a form that the valve exhibits a predetermined 
behavior as a reaction to predetermined flow conditions. 
For further explanation, it is assumed that the pressure P3' in the duct 30 
near the flap always remains constant. This assumption simplifies the 
description, but is of no significance for the mode of operation in 
practice. It is also first assumed that the configuration of the 
installation remains unchanged. This assumption is then abandoned in the 
following when the changed positions according to FIGS. 11 and 12 are to 
be explained. 
At "full" state (FIG. 8) the pressure P2' exerts a force on the lower wing 
76 in chamber 28, which generates a moment of rotation (torque) in 
clockwise direction (that means in the opening direction). The air also 
exerts a force onto the wing 78, which according to the Bernoulli equation 
depends upon the pressure P2' as well as from the quantity of air which 
flows through the opening 72A. The force acting on wing 78 also produces a 
moment of rotation (torque) on the flap 74, which is further explained in 
the following description in connection with the FIGS. 14 and 15. The 
weight of the flap 74 produces forces, which push the flap into the 
resting position according to FIG. 8 in order to close the main flow 
opening 72B. At full state (FIG. 8) the closing forces are still 
sufficient to overcome the resultant of the torques generated by the wings 
76, 78. Despite this, the quantity of air which flows through the opening 
72A is relatively small, because the chamber 24 is full (or rather should 
be full) and separates the expansion chamber 28 from the air supply in the 
feed duct. 
If the height of the column in chamber 24 decreases, the pressure P2' in 
chamber 28 increases. The quantity of air entering the chamber 28 at the 
same time increases. The size of the surface of the wing 76 exposed to the 
pressure P2' can be chosen in such a way that during rising pressure P2' 
the moment of rotation in the clockwise direction increases rapidly. 
Accordingly, the flap 74 has to turn in the clockwise direction and thus 
an air flow begins to pass through the opening 72B, which further "opens" 
the flap, at the same time throttling the flow through the opening 72A. At 
the empty state (FIG. 9), a relatively high pressure P2' acts on the 
surface of the wing 78 and produces closing forces. The chamber 24, 
however, is practically empty and offers only a low resistance to the air 
flow from the feed duct. Therefore, a large quantity of air flows through 
the opening 72B and the corresponding forces on the wing 76 are sufficient 
to overcome all the closing forces. 
The momentary position of the flap 74 clearly depends on the changes in the 
air conditions which develop due to the variation of the filling level. 
Such changes result in a reduction (increase) of the pressure P2' as well 
as a reduction (increase) of the air quantity flowing into the chamber 28. 
This means that during filling level changes, the effects of the 
corresponding changes in pressure and quantity of air reinforce each other 
within the chamber 28. 
The system is thus less dependent on small variations of the flow 
conditions within the feed duct, because the effects of changes in the 
conditions, according to FIG. 7, at least partially balance themselves for 
the valve of an individual chute. A reduction of the pressure P1' is 
accompanied by the increase of the conveyed air quantity. The valve 
according to FIGS. 8 and 9 reacts, however, to the pressure difference 
(P3'-P2') as well as to the flowing quantity of air, this in relation to 
the closing forces as well as in relation to the opening forces of the 
valve. 
The position of the flap basically remains dependent upon the "pressure 
reference level" in the feed duct, so that when the installation 
configuration is changed, the flap at full state (for instance) takes on a 
position according to FIG. 11 and at empty state a position according to 
FIG. 12. This means that the "basic setting" of the flap has shifted, so 
that also at a full feed chamber the opening 72B is not fully closed, and 
the opening 72A at an empty chamber does not anymore reach its maximum 
possible flow section. Accordingly, in spite of a full chamber, air flows 
pass both openings 72A and 72B. The arrangement can, however, be made in 
such a way that the total flow is still kept below a tolerable limit. 
Above this limit, the compression of the uppermost portion of the material 
column in the chamber 24 increases considerably and the quality of the 
delivered material is prejudiced. The suitable arrangement for the 
individual case has to be determined empirically. The following data, 
however, represent an example as guidelines: 
width B1 of the wing 78: 400 mm 
width B2 of the wing 76: 345 mm 
length L1 of the wing 78: 30 mm 
length L2 of the wing 76: 100 mm 
possible pressure level within the feeding duct: from 0 to 2000 Pascal 
quantity of air conveyed: 
duct: 0.4 to 1.2 m.sup.3 /s 
chute: 0.05 to 0.8 m.sup.3 /s 
In this example (in contrast to the example according to FIG. 10) the width 
B1 is chosen somewhat larger than the width B2. 
The invention is not limited to the illustrated example. Rectangular wings 
76,78 are not essential. The axis 80 can be supported by two bolts that 
protrude into the opening 72 from both sides. One wing can be arc-shaped 
in the direction away from the axis. The flap can be made from plate, for 
instance metal or plastic. The effectiveness of the force of gravity can 
be influenced through the choice of the thickness of the sheet. 
Preferably, however, the mass of the wing is kept as low as possible. 
The opening can be specifically formed in order to define a "frame" for the 
flap and thus to cause specific effects of the air flow. The flap can be 
biased so that it does not need to be erected in the shown position. 
The valve according to the invention can also be delivered as a "retrofit 
set" for existing installations. This set of equipment can for instance 
include a support frame and a flap fitted within it, whereby the frame is 
provided with fastening means (for instance screw holes) to facilitate the 
mounting in existing installations. 
By means of a valve according to the FIGS. 8 to 12 it is possible to obtain 
a valve characteristic which is similar to the one of FIG. 4 in the 
previously mentioned European Patent Application 563700, see FIG. 13. The 
behavior of the valve is characterized in that the flap 74 at low flow 
quantity Q fully opens itself and in that thereafter it assumes over a 
wide flow range Q1.fwdarw.Q2 a practically constant flow resistance 
(pressure difference Pa=P2'-P3'). The range Q1-Q2 corresponds with the 
normal operating range of the valve. At a further increase of the flow 
quantity Q, the valve causes a further increasing pressure 
difference--this however lies outside the previously mentioned normal 
operating range. 
It is possible, however, to adjust the behavior of the valve to the 
required specifications, for instance through a different shape of the 
wings 76,78. The embodiment according to FIG. 8 to 12 comprises 
flat-shaped wings. FIGS. 14 and 15 each shows an alternative design of the 
wing 78. In both cases the wing 78A, 78B respectively, has an arc 
shape--in one case (FIG. 14) the wing 78A is shaped concavely, in the 
other case (FIG. 15) it is shaped convexly, each seen in the direction of 
the flow. 
The wall 70 can be furnished with a counterpiece 70A, 70B respectively, to 
correspond with the specifically designed wing 78A, 78B respectively. With 
the design of the wing 78 it is possible to influence the sense of the 
direction of the moment of rotation, effected by this wing. Possible 
effects to be obtained are: 
the kinetic energy of the air flow is at least partially changed into a 
static pressure, which forces the wing 78 into a counterclockwise 
direction (closing force), 
the flow effects a vacuum on the surface of the wing, limiting the opening 
72A, whereby said vacuum effects a moment of rotation in clockwise 
direction (opening force). 
The value of these forces depends on the form (curvature) of the wing as 
well as on its dimensions (L.times.B).