Abstract:
A valve ( 13   a ) is described comprising: a housing ( 50 ) having a fluid inlet for ( 54 ) receiving a flow of compressed fluid and a fluid outlet ( 55 ); a flow duct ( 60 ) movably mounted with respect to the housing, the duct ( 62 ) having a fluid inlet ( 62 ) for receiving a flow of compressed fluid and a fluid outlet ( 65 ), the fluid outlet being positioned around at least a part of the circumference of the duct and being dimensioned to provide a different flow rate at different sections or positions around the circumference of the duct; the fluid outlet of the housing being alignable with a portion of the fluid outlet of the duct to provide a flow rate related to the relative position of the portion of the fluid outlet of the duct and the fluid outlet of the housing; and, a drive element ( 70 ) for moving, e.g. rotating, the duct with respect to the housing such that a desired portion of the fluid outlet of the duct aligns with the fluid outlet of the housing. The valve may operate as a so-called throttle valve. It is an advantage that the valve is quickly movable into a desired relative position in order to regulate fluid flow through the valve. The valve is designed to have a long operational lifetime as, even if the outer surface of the duct wears, the outlet will not substantially change in size and the throttling effect will remain substantially the same.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a valve especially a throttle valve, as well as to a method of operating the valve, a method of manufacturing the valve and to use of the valve in the field of weaving, e.g. in jet weaving. The present invention also relates to a weaving loom comprising the valve and a method of weaving using the valve. 
       BACKGROUND TO THE INVENTION 
       [0002]    In an air jet weaving system, compressed air is used to draw weft threads from supply spools and to blow them into the shed of an air jet loom. A set of relay nozzles is used to support the movement of the weft thread across the shed, which may be several metres in width. Additional nozzles at the far end of the shed may stretch an inserted thread during a weaving operation. An example air jet loom is described in U.S. Pat. No. 4,534,387. 
         [0003]    It is known to adjust the airflow to the main or to the relay nozzles according to the kind of weft thread to be woven. For example, a smooth and strong filament yarn can be woven with a high airflow at the relay nozzles while a weak spun yarn, or a spun yarn with several irregularities, can be woven only with a lower airflow at the relay nozzles. In order to successively insert two or more kinds of weft threads, the airflow of the relay nozzles can be set at a value required by the weakest type of weft yarn so that the weft yarn is not blown apart, broken or damaged. 
         [0004]    U.S. Pat. No. 4,534,387 provides two airflow rates for the relay nozzles and selects the correct airflow such that a yarn will not be blown apart and such that the yarn will be inserted across the shed to arrive timely at the other side or far end of the shed. The weaving machine speed is adapted to suit to the slowest yarn. This machine requires a separate pressure-reducing valve for each required airflow rate. 
         [0005]    U.S. Pat. No. 6,062,273 describes an electrically actuated throttle valve for an insertion nozzle. The throttle valve comprises a plunger which is movable, in a linear direction, within a bore hole. The plunger can be positioned at a desired distance from a valve seat. This type of valve is relatively slow to operate. In situations where the airflow rate needs to be varied for each insertion, the valve has to operate in a period of less than 35 msec. A second problem with this type of valve is that it has a rubber sealing ring which surrounds the plunger to prevent compressed air from escaping from the valve. This sealing ring is prone to wear and thus this type of valve has a limited life time when used in situations where the airflow rate needs to be varied for each insertion. 
         [0006]    It is desirable to have a reduced number of valves as these valves are expensive and are volume/area consuming items. It is also desirable to provide a valve which has a long life time and which does not wear so rapidly. Further, it is also desirable to have a rapidly operating valve. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention seeks to provide an improved valve as well as a method of operating the valve, a method of manufacturing the valve, use of the valve in the field of weaving, e.g. in jet weaving, a weaving loom comprising the valve and a method of weaving using the valve. An advantage of the present invention is rapid speed of operation allowing airflow rate to be varied for each insertion and even during an insertion of a weft thread in a weaving loom. 
         [0008]    A first aspect of the present invention provides a valve comprising: 
         [0009]    a housing having a fluid inlet for receiving a flow of compressed fluid and a fluid outlet; 
         [0010]    a flow duct movably mounted with respect to the housing, the duct having a fluid inlet for receiving a flow of compressed fluid and a fluid outlet, the fluid outlet being positioned around at least a part of the circumference of the duct and being dimensioned to provide a different flow rate at different sections or positions around the circumference of the duct; 
         [0011]    the fluid outlet of the housing being alignable with a portion of the fluid outlet of the duct to provide a flow rate related to the relative position of the portion of the fluid outlet of the duct and the fluid outlet of the housing; and,
       a drive element for moving the duct with respect to the housing such that a desired portion of the fluid outlet of the duct aligns with the fluid outlet of the housing. The valve may operate as a so-called throttle valve.       
 
         [0013]    A valve of this kind has an advantage of being quickly movable into a desired relative position in order to regulate fluid flow through the valve. The duct can be formed with a thin tubular wall which makes the duct lightweight and with low inertia. A valve having a tubular duct having a fluid outlet allowing a different fluid flow around the circumference of the duct allows to dimension the outlet of the duct in a simple manner to provide a different fluid flow rate through the valve. The rapid speed of operation allows a fluid flow rate to be varied at each insertion and even during the insertion of a weft thread. The valve is designed to have a long operational lifetime as, even if the outer surface of the duct wears, the outlet will not substantially change in size and the throttling effect will remain substantially the same. 
         [0014]    It is preferred that the valve comprises a flow duct mounted rotatably with respect to the housing and a drive element for rotating the duct with respect to the housing. The duct of such a valve only needs to be rotated by a small angular distance, which can be achieved rapidly and reliably. Such a movement can normally be done more quickly than a movement in a valve which operates by linear movement along a borehole. 
         [0015]    It is preferred that the valve is not provided with a seal with moving parts which could wear and become unreliable. Particularly, there is no seal provided with respect to the flow duct. The valve can have a means for impeding fluid flow by an amount determined by the position of the fluid outlet of a duct. To this end or in applications where an on-off function is required, a shut-off valve can be positioned downstream of the throttle valve. 
         [0016]    It is preferred that the drive element, such as a motor and coupling device, is positioned within the flow path through the valve. This has an advantage of avoiding the need for a seal between a moving valve element and the housing to prevent fluid escaping from the housing. It also has an advantage of cooling the drive element. 
         [0017]    Preferably, the drive means, such as a motor, has a drive shaft which is mounted coaxially with the longitudinal axis of the duct. 
         [0018]    The fluid inlet of the duct can be located in an end face of the duct. More particularly, the inlet may be positioned around the circumference of the duct at a position spaced along the duct from the fluid outlet and can take the form of a set of apertures, e.g. holes or slots in the wall of the duct. This allows the drive element to connect to the end face of the duct and to use a duct with a small the diameter, which further reduces the weight of the duct and its moment of inertia. This improves the ability to quickly move into a desired angular position. 
         [0019]    The fluid outlet of the duct can comprise a slot around a part of the circumference of the duct or a set of holes, with the size of individual holes and/or the density of holes in the set differing around the circumference of the duct. 
         [0020]    In order that the outlet of the duct can maintain a simple fitting to the fluid outlet of the housing through a range of angular positions, it is preferred that both the flow duct and the part of the housing in the region of the fluid outlet are cylindrical. The remainder of the duct can be of a different shape although, for ease of manufacture and cost, it is preferred that the entire duct is substantially cylindrical. 
         [0021]    The invention has a particularly advantageous application in the field of air jet weaving but the invention is not limited to this application. 
         [0022]    The use of valves according to the invention in an airjet loom also allows use of one air tank for all the relay nozzles and also for the main nozzles. Of course a limited number of air tanks may still be used that can supply air at a given pressure to a respective relay or to a respective main nozzle via a valve according to the invention. 
         [0023]    Further aspects of the invention provide a controller for controlling operation of a valve according to the invention. The control functionality described here can be implemented in software, hardware or a combination of these. Accordingly, another aspect of the invention provides software for controlling operation of the valve. The software may be stored on an electronic memory device, hard disk, optical disk or other machine-readable storage medium. The software may be delivered as a computer program product on a machine-readable carrier or it may be downloaded directly to the controller via a network. Further aspects of the invention include a manufacturing method for such a valve, a weaving loom comprising such a valve and a method of operating such a valve. 
         [0024]    A further aspect of the invention provides a valve assembly comprising: 
         [0025]    a housing having a fluid inlet for receiving a flow of compressed fluid, a fluid outlet and a flow path joining the inlet and the outlet; 
         [0026]    a valve member comprising a tubular flow duct movably mounted within the flow path which is operable to regulate flow along the flow path by positioning the fluid outlet of the duct, more particularly by aligning a portion of the fluid outlet, with respect to the outlet of the housing; and, 
         [0027]    a drive element for operating the valve member, the drive element being mounted in the flow path. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]    Embodiments of the invention will be described with reference to the accompanying drawings in which: 
           [0029]      FIG. 1  schematically shows a jet weaving machine in which the invention can be used; 
           [0030]      FIG. 2  shows a first embodiment of a throttle valve for use in the machine of  FIG. 1 ; 
           [0031]      FIG. 3  shows a second embodiment of a throttle valve for use in the machine of  FIG. 1 ; 
           [0032]      FIG. 4  shows a cross-section of a variant of a duct as in  FIG. 3  near its outlet; 
           [0033]      FIG. 5  shows the outlet of the valve shown in  FIG. 3  in more detail, and; 
           [0034]      FIG. 6  shows a third embodiment of a throttle valve for use in the machine of  FIG. 1 . 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0035]    The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but the invention is only limited by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. Where the term “comprising” is used in the present description and claims, it does not exclude other elements or steps. Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein. 
         [0036]    The present invention will mainly be described with reference to the use of a throttle valve in a weaving loom. Other applications of such a valve are in textile machines whereby a different fluid flow through the valve is required to provide a different fluid flow through a nozzle or similar device of the textile machine. In addition, the term “throttle valve” should not be interpreted as including any limitations other than those in the attached claims. 
         [0037]      FIG. 1  shows an overall schematic view of a weft insertion system of an air jet weaving loom. Three main jet nozzles  2   a ,  2   b ,  2   c  and three additional main jet nozzles  2   d ,  2   e ,  2   f  are shown. Each main nozzle  2   a ,  2   b ,  2   c ,  2   d ,  2   e ,  2   f  is supplied with air from a reservoir  5  via an adjustable throttle valve  11   a ,  11   b ,  11   c ,  11   d ,  11   e ,  11   f  and a shut-off valve  10   a , lob,  10   c ,  10   d ,  10   e ,  10   f  which are described more fully below. The reservoir  5  comprises pressurised air at a given pressure. A weft preparation device  7   a ,  7   b ,  7   c  draws off a weft thread  8   a ,  8   b ,  8   c  from a corresponding yarn supply spool  9   a ,  9   b ,  9   c . Each supply spool  9   a ,  9   b ,  9   c  may be provided with a different kind of weft thread, e.g. weft threads having different properties, such as e.g colour or thickness. The weft preparation device  7   a ,  7   b ,  7   c  stores the weft thread  8   a ,  8   b ,  8   c  on a winding drum and releases the required length of the weft thread  8   a ,  8   b ,  8   c  at the proper moment in the weaving cycle to be inserted into the shed  1  by means of the associated jet nozzles  2   a ,  2   d , the associated jet nozzles  2   b ,  2   e  or the associated jet nozzles  2   d ,  2   f . The shed  1  is formed in a known manner between two planes of warp threads. The weft threads  8   a ,  8   b ,  8   c  may be inserted in the warp shed  1  according to a predefined sequence which is programmed in controller  20 . Several sets of relay nozzles  4   a ,  4   b , . . . ,  4   x  are positioned across the shed  1 , and serve to carry a weft thread  8   a ,  8   b ,  8   c  across the shed  1 . The relay nozzles  4   a ,  4   b , . . . ,  4   x  are supplied with air from reservoir  5  via a further throttle valve  13   a ,  13   b , . . . ,  13   x  and shut-off valve  12   a ,  12   b , . . . ,  12   x . At the far end of the shed  1  there is a so-called stretching nozzle  3  which serves to stretch an inserted weft thread  8   a ,  8   b ,  8   c . This nozzle  3  is also supplied with air from reservoir  5  via a further throttle valve  15  and shut-off valve  14 . Controller  20  operates the throttle valves  11   a ,  11   b ,  11   c ,  11   d ,  11   e ,  11   f ,  13   a ,  13   b , . . . ,  13   x ,  15  and shut-off valves  10   a ,  10   b ,  10   c ,  10   d ,  10   e ,  10   f ,  12   a ,  12   b , . . . ,  12   x ,  14  to provide a required air flow rate at each moment in the weaving cycle during the weaving operation. For a desired weaving pattern, controller  20  has a set of instructions which determine, amongst others, the required weft threads  8   a ,  8   b ,  8   c , airflow rates for the nozzles, and also valve settings and timings for the throttle valves  11   a ,  11   b ,  11   c ,  11   d ,  11   e ,  11   f ,  13   a ,  13   b , . . . ,  13   x ,  15  and the shut-off valves  10   a ,  10   b ,  10   c ,  10   d ,  10   e ,  10   f ,  12   a ,  12   b , . . . ,  12   x ,  14 . Further a weft thread detector  6  is provided at the far end of the shed  1  in order to determine the arrival of the weft thread  8   a ,  8   b ,  8   c.    
         [0038]      FIG. 2  shows a first embodiment of the throttle valve  13   a  according to the present invention and shut-off valve  12   a  in more detail. The throttle valve  13   a  comprises a housing  50  which connects, in a fluid-tight manner, to an air reservoir  5 . The housing  50  comprises a fluid inlet  54  for receiving a flow of compressed air and a fluid outlet  55 . The fluid-tight seal is provided by bolts  52  and a sealing ring  57 . Housing  50  has a channel  51 , e.g. a bore hole in which a tubular duct  60  is mounted. In this embodiment, duct  60  comprises a thin-walled tube which is cylindrical along its entire length, although other shapes are possible. In a preferred embodiment the tube is formed of metal with a wall thickness of about 0.2 mm or more particularly with a wall thickness less than 1 mm. A drive element, more particularly a motor  70  is mounted between the air reservoir  5  and channel  51  of the housing  50 . A drive shaft  72  extends from the motor  70  and the drive shaft  72  is connected, via a coupling device  74 , to the upstream end of the duct  60 . The drive shaft  72  is aligned with the longitudinal axis  61  of the duct  60 . Duct  60  is supported at the upstream end by the drive shaft  72  and coupling device  74 , and at the downstream end by a sleeve or bearing  58  which fits between the duct  60  and housing  50 . The bearing  58  is formed as a tubular element that is fixed, e.g. glued, into the channel  51  of the housing  50 . The housing  50  has a fluid outlet  55  near the upper face of the housing  50 , e.g. a circular bore hole or a slot-like opening. The fluid outlet  55  comprises an opening in the bearing  58  which is situated in the prolongation of an opening  55  in the housing  50 . The air reservoir  5  can be connected in a known manner to an air supply line (not shown). The housing  50  can be mounted to the frame  53  at a place adjacent to an associated nozzle of the loom. 
         [0039]    Duct  60  has a set of inlet holes  62  at its upstream end. Each of the holes  62  extends from the outer surface of the wall of the duct  60  to the hollow interior of the duct  60 . In this embodiment the holes  62  are located around the entire circumference of the duct, along a band which is almost 50% of the total length of the duct  60 . The number of holes  62  is chosen so as to permit, in use, a good flow of air into the interior of the flow duct  60 , while maintaining sufficient strength of the duct  60  to withstand air pressure and rapid movement of the duct  60 . At the downstream end of the duct  60 , a V-shaped slot  65  is defined in the duct  60 . The slot  65  extends from the outer surface of the wall of the duct  60  through to the hollow interior. The slot  65  extends partially around the circumference of the duct  60 . Clearly, the circumferential length of the slot  65  is limited to a part of the circumference of the duct  60 , otherwise it would dissect the duct  60 . The V-shaped slot  65  aligns with the outlet  55  of the housing  50 . The outlet  55  is dimensioned such that it overlaps only a portion of the slot  65 . As noted above, duct  60  is rotatable about longitudinal axis  61 . In use, motor  70  turns drive shaft  72 , and thus tube  60 , into a particular angular position. The position of the slot  65  with respect to the outlet  55  defines what part or portion of the slot  65  is aligned with the outlet  55  and thus regulates how much air can flow from the air reservoir  5 , through the duct  60  and through the outlet  55 . In this way it may be possible to regulate the air flow through the outlet  55  between almost no air flow and maximum air flow, e.g. creating a flow through opening from the duct  60  to the opening  55  between 0% or 100% of the opening of the outlet  55 . Of course, according to a variant the flow through opening may also be between for example 20% and 100% of the opening of the outlet  55 . The duct  60  is shaped or dimensioned to provide a different flow rate at different sections around the circumference of the duct  60 , e.g. by the shape of the slot  65  around the circumference of the duct  60 . 
         [0040]    A shut-off valve  12   a  (shown schematically) is mounted downstream of the throttle valve  13   a . A plunger  83  and valve member  82  act on a valve seat and are normally biased into a closed position (as shown) by a spring  84 . The valve member  82  can be moved, e.g. electromagnetically, against the bias of spring  84  into an open position to allow air to flow from the outlet  55  to the outlet  88 . Outlet  88  connects to a main nozzle or to a relay nozzle as shown in  FIG. 1 . 
         [0041]      FIGS. 3-5  show a second embodiment of the throttle valve  13   b  and shut-off valve  12   b . The main differences are in the design of the inlet and outlet of the duct  60 . In this embodiment the inlet comprises a series of slots  62 A. As shown more fully in  FIG. 3 , adjacent rings of slots  62 A are offset from one another. For example, in this embodiment the housing  50  does not include a separate bearing element and the downstream end of the duct  60  is guided directly into the housing  50 . 
         [0042]    The outlet  65 A of the duct  60  comprises a set of holes which form a band around part of the circumference of the duct  60 . The set of holes  65 A are arranged such that the achievable flow rate gradually increases at different sections around the circumference of the duct  60 , thus allowing to achieve a different flow rate or flow through opening of the valve by rotating the duct  60  with respect to the outlet  55  of the housing  50 , from one end of the outlet  65 A to the other.  FIGS. 4 and 5  each show a set of holes  65 A in more detail. It will be appreciated that the pattern of  FIG. 5 , which is shown as a plan view, would be wrapped around the outer wall of the duct  60 . At a first end of the outlet  65 A of the duct  60 , the holes have a small diameter. In this example a sub-set  91  have a small diameter (e.g. 0.25 mm). As one moves towards the second end of the outlet the diameter of each hole increases and the number of holes increases. A second sub-set of the holes has a larger diameter (e.g. 0.5 mm.) A sub-set  92 A of the holes at this diameter are aligned in a linear manner while a second sub-set  92 B of the holes at this diameter are staggered about a centre-line. This staggering increases the achievable flow compared to the linear alignment, while maintaining the strength of the duct  60 . A third sub-set  93  of holes have a larger diameter (e.g. 1.1 mm) and a final sub-set  94  of holes have the largest diameter (e.g. 1.5 mm). In this final sub-set  94  the holes are arranged so that, as one moves in the direction  98  by rotating the duct  60 , there is an increasing number of holes in each row that in use will be arranged in alignment with the outlet  55  of the housing  50 . This modified form of outlet  65 A of the duct  60  has an advantage in that it maintains the strength of the duct  60  better than a slot  65  and can be provided around a greater portion of the total circumference of the duct  60 . Furthermore, the outlet  65  of the duct  60  can be manufactured precisely, more particularly the holes of the outlet  65 A can be manufactured more precisely than the slot  65  in  FIG. 2 . 
         [0043]    In  FIG. 5  also possible positions of the outlet  55  of the housing  50  are shown with respect to the outlet  65 A of the duct  60 . As shown in full lines the outlet  55  of the housing  50  is arranged with respect to the holes of the outlet  65 A of the duct  60  in such a way that the flow through the duct  60  and the outlet  55  of the housing  50  is almost 100% of the flow through a free outlet  55 , while in the position shown in dashed lines the outlet  55  of the housing  50  is arranged in such a way that the flow through the duct  60  and the outlet  55  of the housing  50  is only a fraction of the flow through a free outlet  55 . 
         [0044]    Although  FIGS. 2 and 3  show a different inlet and a different outlet, either of these modifications can be used independently of the other, e.g. combinations of embodiments of  FIGS. 2 and 3  are possible. 
         [0045]      FIG. 6  shows a further embodiment of the invention. In  FIG. 6  the duct  160  has a conical shape, with a wide mouth  161  at the upstream end and a narrower, cylindrical section  162  at the downstream end. The downstream end  162  and outlet  65 A operate in the same manner as described above. This alternative form of inlet has the effect of funnelling airflow towards the section  162 . The mouth  161  provides an easy path for airflow into the interior of the duct  160  and thus there is no need for any holes or slots ( 62 ,  62 A) in the wall of the duct  160 . As in the other embodiments, duct  160  is rotatable about its longitudinal axis  61 . A motor  70  has a drive shaft  72  which is aligned with the longitudinal axis  61 . A set of arms forming a coupling device  73  connect the drive shaft  72  to the duct  160 . There can be two, preferably three or more arms  73 . Air can freely flow between the set of arms into the interior of duct  160 . It can be seen that this embodiment is more complex to manufacture compared to a cylindrical tube  60  shown in the previous embodiments. 
         [0046]    As described above, the entire motor  70 , drive shaft  72 , coupling device  73 ,  74 , and duct  60 ,  160  are mounted in the air flow path between the air reservoir  5  and outlet  55  of the housing  50 . This has the advantage that a flow of air through the valve cools these parts and prevents overheating. It also means that no seal is required between the moving valve member, more particularly duct  60 ,  160  and the external atmosphere. 
         [0047]    According to an alternative (not shown) the air flow can also flow through the motor  70  itself instead of around the motor  70  as shown in  FIGS. 2 ,  3  and  6 . To this end, the drive shaft  72  of the motor  70  may be made of a hollow shaft or the motor  70  may contain channels to allow the flow of air to pass along the motor  70 . 
         [0048]    It is necessary to provide power and a control signal to the motor  70  via a control cable  40  and a connector  41 . This control cable  40  can be fitted through a borehole in the wall of the housing  50 . The borehole should be sealed against air escape, such as by a fluid-tight seal. The sealing requirements are simple since the control cable  40  is arranged stationary. This control cable  40  can according to an alternative embodiment be fitted through a borehole (not shown) in the wall of the reservoir  5 . 
         [0049]    Friction between the duct  60  and the portion of the housing  50  in the region of the outlet  65  can be minimised by a copper or polymer bearing ring  58  in which the duct  60  will rotate. The bearing ring  58  comprises an opening  59  arranged mainly in the prolongation of the opening  55  of the housing  50 . Even if friction occurs, the heat generated due to this friction will be taken up by the airflow passing through the throttle valve  13   a ,  13   b . Although it is not expected that the throttle valve  13   a ,  13   b  will unduly increase temperature, warm air has been found to have a beneficial effect of aiding weft insertion. It is possible that an airflow can flow between the bearing ring  58  and the duct  60 . This airflow will not be disadvantageous because normally this airflow will be small with respect to the airflow through the outlet  65  of the duct  60  and will not or only slowly change in time. 
         [0050]    The position of the duct  60  of the throttle valve  13   a ,  13   b  is determined by motor  70 . Motor  70  can be a stepper motor with a suitable number of steps to permit a required degree of control of the airflow rate. Alternatively the motor  70  can be a servomotor, e.g. a DC servomotor. Feedback of the angular position of duct  60  can be provided from an encoder attached to the duct or to the drive shaft  72  of the motor  70 , e.g. an optical encoder (not shown). It is also possible to use an air flow sensor at the valve outlet  88  or at the outlet  55  of the housing  50  to generate a feedback signal for the air flow. It is also possible to use a pressure sensor at the outlet  88  or at the outlet  55  of the housing  50 . 
         [0051]    An embodiment has been operated with a stepper motor having a total of  80  steps, with  20  steps for high airflow and  60  steps for low airflow. A controller  20  is programmed with the relationship between, on the one hand, the angular position of the drive shaft  72  or the timing of the insertion cycle, and hence angular position of the duct  60 ,  160 , and, on the other hand, the flow rate that this achieves. The position of the throttle valve  13   a ,  13   b  is operated in coordination with the main controller  20  for the air jet loom to set the air flow to a desired rate at a desired time. A control function  22  for the motor  70 , e.g. the different motors  70  of the throttle valves  13   a ,  13   b , can form part of the overall controller  20  of the machine. The control function  22  can receive an input indicative of the required airflow rate, e.g. from the set of instructions  21  for the current textile design, and outputs a control signal which causes the at least one motor  70  at a particular throttle valve  13   a ,  13   b  to move into an angular position which will cause the valve to achieve the desired flow rate. The control function  22  may alternatively reside locally with each motor  70 . In this case, the control signal applied to each motor controller will indicate the required flow rate. Of course, the control of the motors  70  can also occur in dependence of signals of a weft detector  6 , in other words as a function of the arrival of the respective weft thread  8   a ,  8   b ,  8   c  at the weft detector  6 . 
         [0052]    Consider an example weaving operation, which uses three different yarns  8   a ,  8   b  and  8   c , further named A, B and C, each requiring a different airflow rate. With a yarn insertion sequence of ABCABC the throttle valve will normally be operated for each insertion. With a weaving rate of 1200 insertions per minute, it is necessary to operate the throttle valve twenty times every second, i.e. each 50 msec. As is known, in each weaving cycle the insertion time interval is substantially half of the time interval available for one weaving cycle, i.e. the time interval for one insertion and the time interval for beating up the inserted weft against the fell line. If one chooses for moving the duct  60  between two insertions, e.g. during the time interval for beating up, there is about 20 msec to bring the throttle valve in readiness for the next insertion. Even if one chooses to use the practically whole insertion cycle for moving the duct  60  there will only be available 50 msec for moving the duct  60 . Of course other yarn insertion sequences can be used, depending on the desired pattern to be woven. With a yarn insertion sequence of AABBCC it is only necessary to change the throttle valve after every two insertions, as the same yarn, with almost the same properties, is inserted in two consecutive weaving machine cycles. 
         [0053]    Referring again to  FIG. 1 , the throttle valve  13   a ,  13   b , . . . ,  13   x  can be positioned between an air tank or air reservoir  5  and a group of relay nozzles  4   a ,  4   b , . . . ,  4   x  or between a reservoir  5  and a main nozzle  2   a ,  2   b ,  2   c ,  2   d ,  2   e ,  2   f . The shut-off valve  10   a  to  10   f ,  12   a  to  12   x ,  14  is not essential but is preferable.  FIG. 1  shows each time a number of the relay nozzles  4   a ,  4   b , . . . ,  4   x  fed from the same throttle valve  13   a ,  13   b , . . . ,  13   x . Different relay nozzles  4   a ,  4   b , . . . ,  4   x  along the loom may operate at a different airflow rate. For example, the last group of relay nozzles  4   x  may be controlled at a higher airflow than the ones at the beginning of the shed in order to hold the weft at the end of the insertion. The throttle valve according to the invention can be used to select whatever airflow rate is required. Any other function of airflow rates along the shed can be chosen with, for example, a high airflow for some of the relay nozzles and a lower airflow for some of the other relay nozzles. The use of the throttle valve allows to use one main reservoir  5  for all the relay nozzles and possibly also for all the main nozzles. In  FIG. 1  each throttle valve supplies a group of three relay nozzles  4   a ,  4   b , . . . ,  4   x  with air. According to an alternative, each relay nozzle or groups having two, four or more relay nozzles may be supplied with air via a same throttle valve. 
         [0054]    The throttle valve according to the invention can also be used to optimise the airflow through each relay nozzle, which will lead to less airflow and less use of pressure air for the insertion. Using a throttle valve according to the invention an airflow reduction of up to 30% is possible. Another use of the throttle valve is to vary, e.g. increase or reduce the airflow during the insertion, such that for example a large airflow is generated as the weft passes the relay nozzle while a reduced airflow is generated when the weft is farther away from the relay nozzle. Another possibility is to vary the airflow cyclically during an insertion as known from U.S. Pat. No. 3,672,406. 
         [0055]    If the throttle valve is used to provide airflow to a main insertion nozzle, it is desirable to set the throttle valve to a required throttle position before opening corresponding shut-off valve  11   a  to  11   f . If the throttle valve is used to provide airflow to a relay nozzle, the throttle valve can preferably be set to a required throttle position before opening corresponding shut-off valve  12   a  to  12   x . Further advantages can be gained by changing the throttle position while a weft thread  8   a ,  8   b ,  8   c  is being inserted. 
         [0056]    The flow duct  60  that is movable with respect to the housing  50  or with respect to the flow path of the compressed fluid, is in the preferred embodiments shown in the drawings mounted rotatably within the housing  50 . According to an alternative not shown the duct  60  is mounted movable in the direction of the longitudinal axis  61  such that a particular portion of the outlet of the duct  60  will be aligned with the outlet  55  of the housing  50  in order to regulate the fluid flow through the valve. In this embodiment the holes of the outlet  65 A may be arranged longitudinally with respect to the duct  60 , instead of circumferentially as shown in  FIG. 5 . According to a further alternative the duct  60  is movable with respect to the housing  50  both rotatable and longitudinally, for example such that the outlet of the duct  60  moves along a screw line and particular portions of the outlet of the duct  60  will be aligned with the outlet  55  of the housing  50  to regulate the fluid flow through the valve. 
         [0057]    It is also possible that a throttle valve according to the invention is situated downstream of a shut off valve. 
         [0058]    The invention is not limited to the embodiments described herein, which may be modified or varied without departing from the scope of the invention. It is possible to use throttle valves having the same construction or to use, for example, throttle valves having a different construction, more particularly throttle valves having a different construction for feeding an airflow to the main nozzles or to the relay nozzles or to the stretching nozzles.