Abstract:
An adjustable flow control device is provided which has a valve body containing a series of orifices of varying diameter and an indexable valve cover which includes at least one flow conduit which can be positioned and locked in a sealable manner over a chosen orifice while the remaining part of the valve cover closes off the other orifices of the valve body. Due to the device having fixed size orifices, each orifice will provide a fixed specific fluid flow rate for any predetermined pressure loss across the orifice. The device is suitable for use on all types of gas and liquid fluids.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT 
     Not applicable. 
     INCORPORATION-BY-REFERENCE OF MATERIALS SUBMITTED ON A COMPACT DISC 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a flow control device. It is particularly, but not exclusively, concerned with an adjustable flow control device which contains a plurality of orifices of varying diameter. 
     2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98 
     There are many applications in the air and gas industry where a dependable and constant flow of air or gas is required. In particular, for twin tower pressure swing devices as used for compressed air drying and gas generation, a fixed orifice valve is particularly useful. An inherent part of such pressure swing devices is the use of a purge or re-generating stream of compressed air or gas from the high pressure ‘on-stream’ tower to the low pressure regenerating ‘off-stream’ tower. In all cases this purge air or gas effectively re-conditions the sorbent in the ‘off-stream’ tower. 
     The design of control valve arrangements on pressure swing devices varies considerably but in its simplest form, the tower switching is typically done using two shuttle valves and two exhaust valves which have proved both cost effective and extremely reliable. A variation on this valve arrangement is to use a shuttle valve for switching the inlet flow from one tower to the other and using two non-return valves for controlling the outlet flow of each tower. Non-return valves have the advantage of providing a means to prevent back flow through the pressure swing device which can cause severe damage to the sorbent. In such configurations the purge flow normally travels through a conduit in a by-pass arrangement circumnavigating the non-return valves however U.S. Pat. No. 8,262,784 and EP 2205339 describe a non-return valve with a single integral fixed orifice. The vast majority of such non-return valves are circular in design and are spring loaded in a normally closed position to prevent back-flow. However under normal process flow conditions the pressure differential across the valve forces the valve open to allow the process gas to pass downstream. 
     The proportion of purge flow to process flow is controlled by either an adjustable variable area flow control valve or a fixed orifice arrangement. Variable area control valves are relatively expensive and require a flow meter to set the correct proportion of purge flow furthermore they can be easily tampered with by unskilled operators causing the drier to work inefficiently. Although the use of fixed orifice valves is extremely useful and cost effective they also have a significant problem in that the orifice size is normally pre-set at the factory in line with a pre-ordered specification, and cannot easily be changed on site as generally a replacement serviceable component is required. Pressure swing devices have many variables affecting the required purge flow rate, for instance: change in pressure or temperature, change in process flow, change of required dew point, change of generated gas quality (i.e. purity of generated gas) and even change of altitude. It would therefore be extremely useful to have an adjustable flow control valve which could be easily and precisely adjusted to suit the conditions on-site. 
     One object of the present invention is to address the above problem. 
     BRIEF SUMMARY OF THE INVENTION 
     At their broadest, the flow control devices of the present invention contain a plurality of orifices of different sizes such that the flow rate of gas/liquid through the device can be selectively controlled. 
     A first aspect of the present invention provides a flow control device having a first element and a second element, wherein: the first element has a plurality of first orifices each of a predetermined cross-section; and the second element has a second orifice, and wherein the first and second elements are selectively and sealingly engagable in a plurality of positions, in each of said positions the second orifice being aligned with a different one of said first orifices so as to permit fluid communication through the device via said second orifice and the selected first orifice. 
     In the flow control device of this aspect, the plurality of first orifices each provide a fixed specific fluid flow rate for any predetermined pressure loss across the orifice. 
     Preferably the plurality of first orifices are each of a different cross-section. 
     Preferably the second orifice can be positioned and locked in a sealable manner over a chosen first orifice whilst the remaining part of the second element closes off the other first orifices. 
     The flow control device can be used on all types of gas and liquid fluids. 
     By using a device with selectable fixed orifices instead of a single variable area valve, the flow rate for each selected orifice is pre-set, whereas variable area valves need flow meters and fine adjustment to set a specific flow rate. 
     Preferably the second orifice has a cross-section which is greater than that of each of said first orifices. 
     Preferably the flow control device also has a third element, wherein the first element is mounted to the third element in a predetermined arrangement and the third element and the second element cooperate to seal the first element between them. 
     In this configuration, the first element may be a disc having the plurality of first orifices, whilst the second and third elements are a valve cover and body respectively. The disc can then be mounted in the valve body and the valve cover connected to the valve body so as to align the second orifice with the selected first orifice. 
     This configuration provides for the ability to easily interchange discs. This can be especially useful where large numbers of orifices need to be provided as they can be split between two or more discs. The disc can be sealed with the valve body and cover by using suitable gaskets or bonding with a suitable sealant or simply over moulding the disc to the body or cover. 
     The first element may be rotationally fixed relative to either the second element or the third element and the second element and third element may each have a plurality of splines equal to the number of first orifices, so that the second element and third element can be selectively engaged in a plurality of positions, each corresponding to the alignment of said second orifice with a different one of said first orifices. By providing the splines, which may include a female recessed portion on one element and a male hub portion on the other, the second and third elements are constrained to only engage in configurations in which the second orifice is aligned with a first orifice. This reduces or removes the need for accuracy by the user in ensuring that the orifices are aligned and/or reduces or removes the possibility that the elements are connected in a manner in which the orifices are not aligned. 
     Alternatively, the first element may have a location tab and the second element or the third element may have a plurality of tab locators equal to the number of first orifices, so that the first element can be selectively engaged in a plurality of positions, each corresponding to the alignment of said second orifice with a different one of said first orifices. The location tab and tab locators constrained the first and second elements to only engage in configurations in which the second orifice is aligned with a first orifice. This reduces or removes the need for accuracy by the user in ensuring that the orifices are aligned and/or reduces or removes the possibility that the elements are connected in a manner in which the orifices are not aligned. The tabs and/or tab locators may have labelling, e.g. as described further below, to indicate the first orifice which is aligned with the second orifice. 
     In the case of a non-return valve the third element may include a plurality of third orifices each of which aligns with a corresponding one of said first orifices. Thus the first element can be seated securely on the third element so that fluid passing through the selected first orifice passes through the corresponding orifice in the third element. If only a single orifice (or a number of orifices less than the number of first orifices) is provided in the third element, a flow path from the selected first orifice to the orifice(s) in the third element will need to be provided. 
     The first element may also incorporate a sector in which there is no orifice (where one would ordinarily be positioned). The selection of this position would effectively shut off and prevent flow through the device, which can be useful for diagnostic or testing purposes. 
     Preferably the plurality of first orifices are circular and are located with each of their centres equidistant from the centre of the first element. This is termed common PCD (pitch circle diameter). If the first element is circular, then the first orifices can be positioned with each of their centres set at the same radial displacement from the centre of the disc. However, it is not essential to have the orifices around a given PCD particularly when a combination of both large and small orifices are used provided that the engagement spline always corresponds with the orifice placement. 
     Preferably a seal is located around the second orifice to ensure that, in use, the first orifice is fluid sealed to the second orifice. This will avoid any leakage around the connection between the first and second orifices. 
     The flow control device may further include an alphanumeric register aligned with each of said first orifices, so that the selected first orifice can be identified, e.g. by a user. Preferably the alphanumeric register is provided on the outside of the device so that it can be consulted by a user to determine which orifice is selected without the need to take the device apart. Alternatively one of the elements not bearing the alphanumeric register may be provided with a notch which allows one entry in said register to be observed, so that the changing alignment of the register with that element causes a different entry in the register to be visible. 
     The flow control device may further include a filtering device positioned upstream of said second orifice (or on either or both sides of the second orifice). The filtering device can thus prevent the orifice from being blocked by foreign matter. 
     Preferably the first element is metallic with the orifices produced by laser cutting. 
     Producing a series of accurate orifices can be problematic and time consuming especially when there are a large number of differently-sized orifices. If the first element is made of metal then an option is to drill the orifices. However, as each orifice is of a different size this would require many tool changes all of which takes time. The first element could be made from plastic, in which case it is possible to mould the part with different size orifices in one shot but plastic moulding can also be problematic with worn tools producing flash or inaccurate holes due to processing parameters or tool wear over a period of time. 
     Laser machining is quick and can produce extremely accurately dimensioned orifices. The laser machining may also be used to create other features on the first element, for example to allow for connection with the third element (if present). 
     In certain embodiments, the first element may be metallic and have one or more locating elements laser cut to ensure correct orientation of the first element to the second or third element. The locating elements may be designed to ensure the correct location no matter which orientation the first element is engaged with the other elements, thereby providing a “poka-yoke” system. 
     The flow control device may also act as a non-return valve. This allows the flow control device to be used in configurations where reverse flow through the device would be disadvantageous or even dangerous. 
     The device of the present aspect may include any combination of some, all or none of the above described preferred and optional features. 
     A second aspect of the present invention provides a pressure swing device including two towers in fluid communication with each other and at least one flow control device according to the above first aspect, including any combination of some, all or none of the preferred and optional features of that aspect for controlling the fluid flow between said towers in at least one direction. 
     Pressure swing devices have many variables affecting the required purge flow rate, for instance: changes in pressure or temperature, changes in process flow, changes of required dew point, changes of generated gas quality (i.e. purity of generated gas) and even changes of altitude. As the pressure swing device of this aspect has a flow control device which is adjustable between a range of different known flow rates, the flow between the towers can be easily adjusted to suit the conditions on-site. 
     A third aspect of the present invention provides a pressurised gas or fluid system including a flow control device according to the above first aspect, including any combination of some, all or none of the preferred and optional features of that aspect. 
     A fourth aspect of the present invention provides a desiccant or other sorption cartridge for use within a pressure swing device incorporating a flow control device according to the above first aspect controlling the fluid flow to or from the cartridge in at least one direction. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which: 
         FIG. 1 a    shows a flow control device according to an embodiment of the present invention; 
         FIG. 1 b    shows the flow control device of  FIG. 1 a    in exploded form; 
         FIG. 2 a    shows the flow control device of  FIG. 1 a    from the rear; 
         FIG. 2 b    shows the flow control device of  FIG. 2 a    in exploded form. 
         FIG. 3  shows a cross section through a valve according to a further embodiment of the present invention; 
         FIG. 4  shows a sectional view taken along the line A-A of the valve in  FIG. 3 ; and 
         FIG. 5  shows a section view through a valve according to a further embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A first embodiment of the flow control device is a valve consisting of three parts: a valve body  1 , a circular orifice plate  2  and a circular valve cover  3  as shown in  FIGS. 1 and 2 . 
     The orifice plate  2  is a circular disc with a series of various diameter orifices  21  positioned around a common PCD (pitch circle diameter), i.e. with each of their centres set at the same radial displacement from the centre of the disc. The diameters of these orifices  21  are known and recorded. 
     The orifice plate  2  has a central circular hole  22  with two locating pins  23  which engage with notches  13  in a locating ring  12  on the body  1  to position the orifice plate  2  both centrally and rotationally with respect to the body  1 . A different number of locating pins  23  could be used to the same effect, or the shape of the central hole could be selected to match a similarly shaped protrusion or recess on the body  1 . Preferably the locating pins or other means of locating do not have rotational symmetry so that the orifice plate  2  can only be located in a single orientation with respect to the body  1 . Furthermore, the locating pins  23  are designed to ensure the correct location no matter which orientation the orifice plate  2  is fitted to the valve body  1 , thereby providing a “poka-yoke” system. 
     The body  1  has a plurality of orifices  11  which match in number to the orifices  21  in the orifice plate  2 . Towards the centre of the internal face of the body, a locating ring  12  is provided which protrudes slightly from the face. This locating ring  12  matches to the central circular hole  22  of the orifice plate, thereby locating and retaining the orifice plate in relation to the body  1 . The locating ring  12  has two notches  13  which engage with the locating pins  23  on the orifice plate to retain the orifice plate in a fixed rotational position relative to the body and thereby ensure that the orifices  11  in the body  1  are aligned with the orifices  21  in the orifice plate  2 . 
     The body  1  has a circular recessed female splined hole  14  around the outer circumference of the internal face for engagement with the valve cover  3 . The number of splines is equal to the number of orifices  21  in the orifice plate  2 . 
     In the centre of the internal face of the body  1  is a fixing means  15 , such as the blank female threaded hole shown in  FIG. 2 b   . This allows the orifice plate  2  and valve cover  3  to be fixed to the body  1  and a fluid-tight seal made. 
     Advantageously the body has an alphabetical or numerical register aligned with the series of orifices  11  which can be cross referenced against a table of known performance characteristics to ensure the correct orifice  21  is used for each application. This register could be printed, inscribed or moulded on the outer circumference of the body  1  and aligned with each spline of the hole  14 . The register can be observed through a notch  34  to ensure correct positioning. 
     The valve cover  3  is typically of the same diameter as the internal face of the valve body  1  and has a single orifice  31 . The orifice  31  is at least equal to, or larger in diameter than the largest diameter orifice  21  in the orifice plate  2  and is located on the same PCD as the orifices  21  in the orifice plate  2 . 
     The cover  3  has around its circumference a circular male splined boss  32  dimensioned to fit the splines  14  in the valve body  1 . The interaction between the boss  32  and the splines  14  rotationally fixes the cover  3  and the body  1  relative to each other, thereby fixing the position of the orifice  31  in the cover  3  relative to the orifices  21  in the orifice plate  2 . 
     In the centre of the cover  3  is a through hole  33  through which the locking device  41  passes to engage with the fixing means  15 . The locking device  41  is typically in the form of a bolt which engages with the threaded hole  15  in the body and bears against the cover  2  to hold the two parts together in use. 
     The single orifice  31  in the valve cover  3  may be provided with a filtering device on the upstream side to prevent the orifice  31  from being blocked by foreign matter. 
     The various parts of the device can be manufactured from plastic or metal depending on the application requirements. 
     The orifice shape of all of the orifices  11 ,  21 ,  31  can take any form such as square, oval, hexagonal etc. but for sake of practicality a circular round orifice is preferred. It is also preferable that the orifices are all of the same cross-sectional shape to avoid or reduce the turbulent flow associated with movement of the fluid past orifices of different shapes. 
     Producing a series of accurate orifices can also be problematic and time consuming especially when the orifice plate  2  may have twenty or more differently-sized orifices  21 . If the orifice plate  2  is made of metal then it is normal to drill orifices. However, as each orifice  21  is of a different size this would require many tool changes all of which takes time. If the orifice plate  2  is made from plastic then it is possible to mould the part with different size orifices  21  in one shot but plastic moulding can also be problematic with worn tools producing flash or inaccurate holes due to processing parameters or tool wear over a period of time, etc. 
     In the present embodiment these problems are addressed by the orifice plate  2 , which is a pre-holed annular disc sandwiched between the valve body  1  and valve cover  3 . The orifice plate  2  can be made from plastic but is preferably made from a corrosion resistant metal such as brass or preferably stainless steel. 
     Such discs can be pressed, water jet cut or laser cut from sheet steel. Advances in water jet and laser cutting technology lends itself to producing such discs and when the orifices are cut in this way, it is quick, extremely accurate and cost effective especially with today&#39;s computer controlled machines. At the same time as producing the series of orifices the cutting machine can also cut female registering locations  22 ,  23  which will coincide with male registering locations  12 ,  13  in the valve body  1 . These registering locations ensure the orifice plate  2  is always located in the correct position. Another feature of these techniques is the ability to etch meaning that all manner of identification markings can be added to the disc, such as part numbers or the register information to allow a user to identify which size of orifice is in use. 
     Whilst it is possible to position the orifice plate  2  on the high pressure or low pressure side of the valve body  1 , it is preferable to position it on the high pressure side as the differential pressure will help aid the orifice plate  2  seal against the valve body  1 . 
     The orifice plate  2  may be interchangeable. This is especially useful when large numbers of orifices  21  need to be used as they can be split between two or more orifice plates  2 . Of course the orifice plate  2  needs to seal with the valve body  1  and cover  3  and this can be done by using suitable gaskets or bonding with a suitable sealant or simply over moulding the disc to the body or cover. 
     Many empirical formulas have been devised over the years to estimate or predict the anticipated flow rate through an orifice which is an accurate sharp edged circular hole. Therefore by inputting the application specific data, typically fluid type and differential pressure, then the flow rate can be closely approximated. This allows the user of the flow control device to select the orifice with the desired flow characteristics based on the size of the selected orifice (which can be determined from the register information) and the application specific data. 
     The embodiment described above relates to a non-moving valve which would normally be held and sealed within a pressure containing receptacle, for example within a pressure swing device, and would have both inlet and outlet conduits. Other embodiments of the present invention provide a pressure swing device incorporating one or more flow control devices according to embodiments of the present invention. 
     In a pressure swing compressed air drier, the inlet would provide high pressure dry air from the ‘on stream’ tower and the outlet would provide extra dry air to the ‘off stream’ regenerating tower. 
     In a further embodiment, the adjustable flow control valve and a non-return valve are combined to provide a dual function valve which provides a means to prevent back flow through the pressure swing device (which can cause severe damage to the sorbent). Function one is when the valve is closed and in this mode it provides a means for controlled purge flow and in function two the valve is open providing unrestricted process gas flow to the outlet port of the device. 
     The non-return valve may be of any known construction, but are typically circular in design and are spring loaded in a normally closed position to prevent back-flow. However under normal process flow conditions the pressure differential across the valve forces the valve open to allow the process gas to pass downstream. 
       FIG. 3  shows a three-part in-line variable purge valve  50  according to a second embodiment of the present invention (although the valve shown is a purge valve, it will be appreciated that valves for other purposes can be made to the same or similar construction). This valve permits purge flow in either direction.  FIG. 4  shows a cross-section along the line A-A in  FIG. 3 . 
     The valve  50  is made up of three primary components: a first manifold  51 , a second manifold  52  and a disc  53  which is sandwiched between the two manifolds. 
     The first manifold  51  has a first port  56  which, in use, is in fluid communication with one of the towers of the pressure swing device. The second manifold  52  has a second port  57  which, in use, is in fluid communication with the other of the towers of the pressure swing device. 
     The disc  53  is sandwiched between the two manifolds  51 ,  52  which are bolted together using a standard 4 bolt flange fixing. Bolts pass through holes  58  in the manifolds and the two manifolds are secured together with an O-ring seal  59  around the disc  53 . 
     The disc  53  has a number of circular orifices  54  cut around a common pitch circle diameter, each having a different, known radius. The disc is mounted in one of a number of predetermined rotational positions on the second manifold  52  as viewed in  FIG. 4  which are arranged such that, in each of the predetermined positions, one of the orifices  54  on the disc is positioned in-line with a single orifice  55  in the second manifold  52 . The single orifice  55  in the second manifold  52  has a greater diameter than all of the orifices  54  cut into the disc  53 . The single orifice  55  may have its own O-ring seal  60  which ensures a fluid-tight seal between the disc  53  and the second manifold  52 . 
     The first port  56  is in fluid communication with the selected orifice  54  in the disc  53 . The orifice  55  in the second manifold is in fluid communication with the second port  57 . Accordingly, fluid can flow from the first port to the second port (or vice-versa) through the selected orifice  54  in the disc  53 , and the rate of flow will be determined by the diameter of the selected orifice  54  and can be readily determined from known information about the diameter of the selected orifice  54  and the properties of the fluid. 
     As shown in  FIG. 4 , the second manifold  52  has a plurality of tabs  61 , each bearing an alphanumeric reference. The number of tabs  61  matches the number of orifices  54  cut into the disc  53 . The disc  53  has an indicator  62  which, when the disc  53  is aligned such that one of the orifices  54  is aligned with the orifice  55  in the second manifold, aligns with one of said tabs  61 . Therefore a user of the valve  50  can easily determine which orifice  54  is in use and, from a reference table or other source, information about that orifice. 
     Either due to the interaction between the tabs  61  and the indicator  62 , or through a separate set of mutually engaging portions, the disc  53  is constrained to only be positioned in a fixed number of rotary positions relative to the second manifold. This number of positions corresponds to the number of orifices  54  in the disc  53 , such that in each position a different one of said orifices aligns with the orifice  55  in the second manifold. 
     It will be appreciated that, where components of this embodiment have not been described in detail, they may have similar properties, functions or characteristics (including any optional properties, functions or characteristics) as described in relation to similar components of the above described first embodiment. 
       FIG. 5  shows a cross-section through a valve  70  according to a further embodiment of the present invention. In contrast to the above described embodiments in which the valve was comprised of three principal components, the valve  70  of this embodiment has two principal components: a first plate  71  and a second plate  72 . 
     The first element  71  has a number of circular orifices  74  cut around a common pitch circle diameter, each having a different, known radius. The first element  71  is mounted to the second element  72  in one of a number of predetermined rotational positions which are arranged such that, in each of the predetermined positions, one of the orifices  74  on the disc is positioned in-line with a single orifice  75  in the second element  72 . The single orifice  75  in the second element  72  has a greater diameter than all of the orifices  74  cut into the first element  71 . The single orifice  75  may have its own O-ring seal  80  which ensures a fluid-tight seal between the first element  71  and the second element  72 . 
     The rotational position of the first element  71  relative to the second element  72  is controlled to be in one of the number of predetermined positions by spline locators  76 . The first element  71  is secured to the second element  72  by a fixing bolt  77  so that the O-ring seal  80  of the single orifice makes a fluid-tight seal between the elements. 
     The valve  70  can be mounted in a pipe  78  or other fluid containing component and fluid flow around the valve is prevented by an outer O-ring seal  79 . A circlip  81  is used to hold the valve  70  in position. 
     It will be appreciated that, where components of this embodiment have not been described in detail, they may have similar properties, functions or characteristics (including any optional properties, functions or characteristics) as described in relation to similar components of the above described first and second embodiments. 
     While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.