Abstract:
An air flow control valve including: a valve body having an internal cavity and an inlet and outlet in flow communication with the internal cavity, the axes of the inlet and outlet being aligned at substantially 90° each other; a valve seat located within the cavity and co-axially aligned with the outlet, the valve sat being located on the distal end of an upstanding tubular pedestal which is famed around the outlet; the internal cavity being configured so as to define an annular space around the pedestal with which the inlet is in flow communication; a flexible generally planar diaphragm mounted above the valve seat, the diaphragm supporting a valve closure member which is adapted to engage the valve seat to close the valve; valve control means for causing the diaphragm to move towards and away from the valve seat to dose and open the valve respectively; and the valve being characterised in that, with the valve oriented with die inlet axis horizontal and the outlet facing downwards, the valve seat is located at an elevation at or below the upper most edge of the inlet, and the diaphragm is located at an elevation above the upper most edge of the inlet.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to a diaphragm operated air flow control valve of the type typically used in the dust collector industry. The valve of the invention will be suitable for use in that industry, but it is to be understood that the valve of the invention can be used in other applications as well.  
       BACKGROUND OF THE INVENTION  
       [0002]     Air flow control valves used in the dust collection industry have a series of reasonably specific design constraints which they must meet in order to operate effectively. For example, typically the valves have inlets and outlets arranged at 90° to each other, the valves are typically electronically controlled, and the supply and outlet pipes which lead towards and away from the valve are typically either 20 mm, 25 mm or 45 mm in diameter.  
         [0003]     Typically these valves have a valve closure member mounted to a diaphragm and by controlling the pressure on opposite sides of the diaphragm the valve can either be opened or closed. The pressurised air supply provides the necessary pressure for controlling the valve and a bleed arrangement is provided for supplying air under pressure to opposite sides of the diaphragm.  
         [0004]     Since these aspects of the valves are well-known, they need not be described in this document in any great detail.  
         [0005]     There are important performance characteristics which such valves must meet in order to be competitive in the industry. For example, the valves must open rapidly and there must be a minimum pressure drop across the valve when the valve is open. In addition, the valves should be relatively easy to manufacture, assemble and install, and maintenance of the valves should be possible without removing the valve body from the equipment onto which is has been installed.  
       SUMMARY OF THE INVENTION  
       [0006]     According to one aspect of the invention there is provided an air flow control valve including: 
        a valve body having an internal cavity and an inlet and outlet in flow communication with the internal cavity, the axes of the inlet and outlet being aligned at substantially 90° to each other;     a valve seat located within the cavity and co-axially aligned with die outlet, the valve seat being located on the distil end of an upstanding tubular pedestal which is formed around the outlet;     the internal cavity being configured so as to define an annular space around the pedestal with which the inlet is in flow communication;     flexible generally planar diaphragm mounted above the valve seat, the diaphragm supporting a valve closure member which is adapted to engage the valve seat to close the valve;     valve control means for causing the diaphragm to move towards and away from the valve seat to close and open the valve respectively; and     the valve being characterised in that, with the valve oriented with the inlet axis horizontal and the outlet facing downwards, the valve seat is located at an elevation at or below the upper most edge of the inlet, and the diaphragm is located at an elevation above the upper most edge of the inlet.        
 
         [0013]     Preferably the upper most edge of the valve seat is located a distance which is approximately one third the diameter of the inlet above the centre line of the inlet.  
         [0014]     Preferably the valve body has a bowl portion in which the inlet and outlet are located, and a cap portion in which the valve control means is located, the cap portion having screw threads thereon adapted to engage with screw threads on the bowl portion, the diaphragm being captively held in position between the cap portion and the bowl portion when the cap portion is operatively screwed onto the bowl portion. The screw threads on the bowl portion are preferably of female configuration, and the threads on the cap portion are preferably of male configuration.  
         [0015]     A further feature of the invention provides for the cross sectional area of the annular space or bowl area relative to the area of the valve seat to be in the range of 2.5:1 to 4.5:1, and preferably in the range of 3.2:1 to 3.6:1.  
         [0016]     The internal diameter of the valve seat is preferably larger than the internal diameter of the outlet, and the inner wall of the tubular pedestal preferably tapers convergently from the valve seat towards the outlet.  
         [0017]     The inlet and outlet can have any suitable connection arrangement for connecting air flow conduits to the valve. In one arrangement the inlet and outlet both have an internally threaded socket adapted to each receive a respective externally threaded tubular conduit.  
         [0018]     The diaphragm can have a bleed hole (such as bleed hole  26  of  FIGS. 1 and 7 A) therethrough adapted to feed pressurised air from the annular space into the area above the diaphragm. Optionally the diaphragm can be spring-loaded into engagement with the valve seat. If desired a combination of a bleed hole and spring bias can be utilised.  
         [0019]     The present invention also provides a valve body and cover, said valve body including a threaded portion to engage a mating threaded portion on said cover, said body and said cover having respective engagement members which are adapted to engage each other in use, said members being positioned so that said cover, when threaded onto said body, will rotate a necessary number of turns to secure said cover to said body to a predetermined torque, indicated by said engagement members engaging each other preventing any further tightening, said engagement members not engaging or contacting until said predetermined torque is reached.  
         [0020]     Preferably it takes 1½ turns to secure said cover from first engagement of the threads of said cover and body until engagement of the respective engagement members.  
         [0021]     The engagement members can be located outside of a circumference of said cover, or alternatively located within a circumference of said cover. Preferably said cover and said body include a releasable securing means so that said cover cannot be unsecured from said body until said releasable securing means has been released.  
         [0022]     Preferably said cover body each have an aperture therein so that once said engagement members are engaged, said apertures are aligned so as to receive a locking means. Preferably said locking means is any one of: a pin; a plastic pin; a cable tie or a retractable pin.  
         [0023]     Alternatively said body can include a system pressure activated pawl, with said cover having a recess or aperture, whereby when said valve is pressurised the pawl moves into said recess thereby locking the cover and body together until depressurised.  
         [0024]     Preferably the threaded portion of one or both of said cover and said body includes at least one groove extending generally laterally relative to the thread direction, said at least one groove permitting the exhaust of gas in said valve body once a seal between said cover and said body is broken.  
         [0025]     The engagement members can be protruding bosses, lugs, faces, pins, or any appropriate formation, or combinations of these, which can extend laterally or axially relative to the valve body and or cover.  
         [0026]     An operator to open and close a control valve having: 
        a body member which is separate from said control valve but is connectable thereto, said body member having a first side with connection means for connection to said control valve and a second side to engage a valve member;     said body member including a passage communicating from said first side to said second side to allow gas from said control valve through said body member when connection has been made;     said body member including a seat around said passage on said second side, which is closable by said valve member, to open and close said passage when desired.        
 
         [0030]     Preferably the valve member is movably held between said body member and a second member which connects to said body member.  
         [0031]     The body member can be made from a plate having on one side connection means to connect either directly or remotely to said control valve.  
         [0032]     Preferably said plate includes support members on said second side extending away therefrom.  
         [0033]     The body member can include a peripheral wall around said plate. Alternatively said body member can be generally cup shaped.  
         [0034]     The second member can be a solenoid casing which is held by or which holds said body member.  
         [0035]     Alternatively the second member can be a tubular member such as a ferrule tube, which is held by or which holds said body member, said tubular member in turn being held by or which holds a solenoid casing.  
         [0036]     The second member being held by support members on said body member so as to be kept a predetermined distance away from said seat.  
         [0037]     The second member having associated therewith a bias means to bias said valve member towards or away from such seat.  
         [0038]     The operator when in use being directly connected to said control valve.  
         [0039]     Alternatively the operator when in use is connected to said control valve by means of a tube allowing the operator to be remotely located relative to said control valve.  
         [0040]     The body member preferably has a plurality of ports formed between a like number of support members extending away from said body member.  
         [0041]     Preferably the valve member is a plunger. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0042]     Further features of the invention will be made apparent from the description of the embodiments thereof given below by way of examples. In the description references are made to the accompanying drawings, but the specific features shown in the drawings should not be construed as limiting on the invention.  
         [0043]     Embodiments are described with reference to the following drawings in which:  
         [0044]      FIG. 1  illustrates an exploded cross-sectional side view of an air flow control valve;  
         [0045]      FIG. 2  illustrates an enlarged cross-sectional side view of the bowl portion of the valve body of  FIG. 1 ;  
         [0046]      FIG. 3  illustrates a perspective view of a valve similar to  FIGS. 1 and 2  with different connecting portions and with the cover removed from the body portion;  
         [0047]      FIG. 4  illustrates an end view of the bowl portion of the body of the valve shown in  FIG. 3 ;  
         [0048]      FIG. 5  illustrates an exploded view of another valve body and cover;  
         [0049]      FIG. 6  illustrates the cover and body of  FIG. 5  in an assembly;  
         [0050]      FIG. 7  illustrates an exploded perspective view of valve components to construct a valve similar to that of  FIGS. 5 and 6 ;  
         [0051]      FIG. 7A  illustrates a perspective view of the valve body and diaphragm of  FIG. 7 ;  
         [0052]      FIG. 8  illustrates an exploded view of an operator or pilot valve for use with the cover of  FIG. 5 , or  6 ;  
         [0053]      FIG. 9  illustrates a cross section of the exploded parts of another operator construction;  
         [0054]      FIG. 10  illustrates a cross section of the operator of  FIG. 9  in assembled condition;  
         [0055]      FIG. 11  illustrates a plan view of an arrangement to lock a cover relative to a valve body when pressurised;  
         [0056]      FIG. 12  illustrates a right side elevation of the valve of  FIG. 11 ;  
         [0057]      FIG. 13  illustrates a cross section through the valve of  FIG. 1  through the plane BB;  
         [0058]      FIG. 14  illustrates a detail of the right hand side of the cross section of  FIG. 13 ;  
         [0059]      FIG. 15  illustrates an exploded view of a pilot valve or operator assembly similar to that of  FIGS. 9 and 10 ;  
         [0060]      FIG. 16  shows the pilot valve or operator assembled from the parts of  FIG. 15 ;  
         [0061]      FIG. 17  illustrates a part cross section through the pilot valve or operator of  FIG. 16 , with the pilot valve or operator in the closed condition; and  
         [0062]      FIG. 18  illustrates a part cross section through the pilot valve or operator of  FIG. 16 , with the pilot valve or operator in an open condition. 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0063]     Illustrated in  FIG. 1  is a flow control valve  2  which includes a valve body  10  having a bowl portion  12  and a cap portion  14 , which in use is mounted to de bowl portion  12  with an O-ring seal  13  to seal the under side of flange  130  of cap portion  14  with a sealing rim  132  at the top of the bowl portion  12 . The cap portion  14  will, in use, hold a diaphragm assembly  16  to the body portion  12 . The valve  2  is controlled by a solenoid operated plunger assembly  18  which includes a plunger  20 , compression spring  22  and a retaining clip  24 . These components are well known in the art and need not to be described herein in any detail.  
         [0064]     The diaphragm assembly  16  has a flexible circular diaphragm  55  which has a valve closure member  20  mounted thereto by means of a fastener  22  and backing plate  24 . The diaphragm  55  has a bleed passage  26  therethrough (see also bleed passage or hole  26  in  FIG. 7A ), through which pressure differentials on opposite sides of the diaphragm  55  are equalised. A compression spring  28  urges the diaphragm away from the cap portion  14 . The plunger  20  has a rubber cap  30  on its lower most end which is adapted to seal with a nozzle  32  which in use is mounted to the cap portion  14 .  
         [0065]     The bowl portion  12  has an inlet  34  and an outlet  36  both of which are in flow communication with an internal cavity  38 . The internal cavity  38  is of a circular or bowl shaped configuration. A valve seat  40 , which is coaxial with and surrounds the outlet  36 , is formed on the bowl portion  12 . The valve seat  40  is located on the upper or distal end of a tubular pedestal  42  which surrounds the outlet  36 . The pedestal  42  serves to lift the valve seat  40  adjacent the under side of the diaphragm assembly  16  which will be mounted against an annular seat  44  formed on the body portion.  
         [0066]     Turning to  FIG. 2  of the drawings, the body portion  12  is shown in more detail. The configuration of the body portion  12  achieves significant efficiencies for the valve.  
         [0067]     The inlet  34  of the body portion  12  has a centre line  45  which, when the body portion is oriented, as shown in  FIG. 2 , with the centre line  45  horizontal and the outlet  36  facing downwardly, the valve seat  40  is located below the upper most edge  47  of the inlet  34 . In other words, the valve seat  40  is relatively close to the centre line  45  of the inlet  34 . In the arrangement shown in  FIG. 2 , for example, where the inlet diameter  34  is approximately 24 mm, the dimension “d” is approximately 9 mm which is significantly less than the applicant&#39;s prior art valve arrangements which is approximately 20 mm. The dimension between the diaphragm seat  44  and the valve seat  40  has also been increased. In the applicant&#39;s prior valve that dimension was approximately 6 mm whereas in the present embodiment that dimension is approximately 9 mm. However, it is believed that it is the lowering of the valve seat  40  in relation to the inlet port centre line which has significantly improved the efficiency of the valve. The effect of these dimensional changes is that when the valve is open, a relatively large opening is achieved between the diaphragm and the valve seat, and the valve seat is also located within the direct flow path of air flowing from the inlet to the outlet. This ensures a significantly lower pressure drop across the valve.  
         [0068]     In addition to lowering the valve seat the applicant has also increased the diameter of the annular space  46  around the pedestal  42 . This has been achieved by an increase in the diameter of the body portion  12 . This larger bowl area allows for a straighter flow path of high pressure air across the valve seat  40  and into the outlet  36  when the valve is open. Furthermore, this arrangement provides a higher static pressure recovery (due to lower air velocity around the bowl) inside the bowl. The higher the static pressure inside the bowl, the better the flow across the seat when the valve is open.  
         [0069]     These new configurations in the valve body have helped to achieve an approximately 40% flow improvement (Kv) against applicant&#39;s own prior art valve of similar external dimensions. The attached Table 1 sets out a comparison of a valve of the present embodiment (being those marked with a suffix “−3” in column 1) and certain of the applicant&#39;s comparable prior art valves (being those with a suffix “std” in column 1).  
         [0070]     Clearly, the applicant does not in any way wish to be bound to any of the dimensions or ratios listed in Table 1 but those dimensions indicate certain of the differences between the prior art valves and the valve of the present embodiment which have gone towards achieving this improvement in flow performance.  
         [0071]     One difference in particular is that the column entitled Bowl Area/Seat Area indicates that for the valves embodying the invention, namely those with a “−3” suffix that this ration is in the range of 2.5:1 to 4.5:1 and more particularly in the range of 3.2:1 to 3.6:1.  
         [0072]     The FS, DD and T are letter codes representing for the inlet and outlet configurations available in the industry. The FS valves generally have a structure where the inlet has a tubular connection with a flange surrounding its end, while the outlet has an unthreaded unflanged tubular construction. The DD valve has male threaded inlet and outlet which cooperates with a gland nut and frusto-conical seal as illustatd in  FIG. 7 . The T valve has an inlet and outlet with female threads as illustrated in  FIGS. 1, 2  and  11  through to  14 .  
                                                                                                     TABLE 1                                   Seat                                               Area           Seat   Bowl   Inlet   Inlet   %           Seat   Seat   (mm2)   Bowl   Bowl   Area/   area/   Ct&#39;line   port   port           ID   OD   (Based   ID   Area   Bowl   Seat   to Seat   dia   dia       Value   (mm)   (mm)   on ID)   (mm)   (mm2)   Area   area   Ht (mm)   (mm)   exposed                                25FS-3   35.00   42.00   962.11   77.00   3271.18   0.20   3.40   14.30   39.40   13.71       25FS std   31.50   42.00   779.31   64.00   1831.55   0.43   2.35   30.80   39.40   −28.17       20FS-3   27.50   32.50   593.96   60.00   1997.85   0.30   3.36   9.00   26.00   15.38       20FS std   23.00   27.40   415.48   51.30   1477.28   0.28   3.56   19.50   25.20   −27.38       20DD-3   27.50   32.50   593.96   60.00   1997.85   0.30   3.36   9.00   256.0   14.00       20T-3   27.50   32.50   593.96   60.00   1997.85   0.30   3.36   9.00   23.90   12.34       20T,DD-std   20.50   25.80   330.06   50.80   1504.04   0.22   4.56   15.20   23.00   −16.09       45FS-3   55.00   63.50   2375.83   120.00   8142.80   0.29   3.43   15.00   46.00   20.00       45FS std   53.50   63.50   2248.00   95.50   3996.10   0.56   1.78   37.90   46.00   −5.80       45T,DD std   50.80   59.00   2026.83   95.50   4429.05   0.46   2.19   37.80   40.40   −10.85                 Notes for Table 1            Seat Area Based on ID column- Seat area is based on ID            Bowl Area Column-Bowl area is based on (bowl ID minus seat OD).            Inlet Centreline to seat height column- Height from inlet port centreline to diaphragm flange.            Inlet port diameter column-Only 25FS-3 dimension quoted against 25FS/T/DD-3 row.            % port dia exposed column-Based on % of port diameter(not area) exposed above body seat.             
 
         [0073]     Other improvements of the valve are that the cap portion  14  has a male threads  48  which engage in female threads  50  formed in the body portion. This allows the cap portion  14  to be screwed onto and off the body portion for quick assembly and maintenance. The plunger assembly, likewise, is simply fitted to the cap portion by the clip  24  which engages in a groove  52 . The cap  14  includes a hexagonal formation  14 ′ to allow a spanner to engage it and also provides gripping formation  14 ″ so that tightening by hand can be performed.  
         [0074]     It will be appreciated that the valve seat  40  could be lowered even closer to the centre line  45  of the inlet. This could be achieved by, for example, increasing in the thickness of the valve closure  20 , thereby bringing the contact face of the valve closure member  20  closer to the valve seat  40 . Also, the increased bowl diameter has the effect of increasing the diameter of the diaphragm  55  allowing more movement of the diaphragm  55  and therefore permitting the valve seat  40  to be located a greater distance away from the valve closure member  20  than is the case with small diameter diaphragms.  
         [0075]     It will be appreciated that maintenance of the valve can take place in a relatively simple fashion. To maintain the valve after it has been installed onto equipment the cap portion  14  is simply screwed off the body portion  12  allowing the diaphragm assembly  16  to be removed and replaced as necessary. The plunger assembly  18  can, similarly, be removed from the cap portion by releasing the clip  24 . This is a simple operation and allows for far quicker maintenance and inspection than is the case where a series of bolts or screws are used to hold down the cap and the plunger assembly.  
         [0076]     It will be appreciated that the simplicity of the valve also enables the valve to be easily and rapidly assembled during manufacture. In addition, the simplicity of the design has significantly reduced the number of parts of the valve and this has therefore reduced the cost of the valve.  
         [0077]     Illustrated in  FIGS. 3 and 4  is a valve body similar to that of  FIG. 2 , except that there are male threaded connections  54  to allow connection to the inlet  34  and outlet  36 . It will be noted that the valve of  FIG. 2  has two female connections. Other valves connections could be provided such as flanges clamped or bolted fitting arrangements.  
         [0078]     Illustrated in  FIG. 5  is an exploded view of a valve  2 A having a cover  14 A and body  10 A similar to valve  2 , cover  14  and body  10  of  FIG. 1 . Many of the components illustrated in previous Figures are not illustrated in  FIGS. 5 and 6  to provide better clarity. The cover  14 A has a male thread  48 A whilst the body  10 A has a female thread  50 A which mates with the male thread  48 A.  
         [0079]     The cover  14 A and body  10 A differ from the cover  14  and body  10  of  FIG. 1  by the presence of a radially extending portion  100  on the cover  14 A and a similar shaped radial extension  102  on the body  10 A. The extension  100  terminates in a face  104  which can engage protruding boss  106  on body  10 A. The height of the extension  100  and the pitch of threads  48 A and  50 A are designed and arranged so that the cover  14 A will be tightened onto the body  10 A after 1½ turns of the cover  14 A. Thus to connect the cover  14 A to the body  10 A the thread  48 A has to begin on cover  14 A in the vicinity of the face  104  whereas the thread  50 A needs to begin at a location diametrically opposite to protruding boss  106 . In this way after the first half turn with the threads engaged, the lower most portion of face  104  will pass close to, but not make contact with, the upper surface  108  of protruding boss  106 . The protruding boss  106  is of a depth or height equal to the pitch of the thread  50 A or  48 A. Thus after one further complete turn the underneath surface of extension  100  and face  104  will be at the same level as the upper surface of extension  102  and the face  104  will be prevented from moving further in a tightening direction by means of the protruding boss  106 .  
         [0080]     In this way, the cover  14 A can not be overtightened onto the body  10 A. The bosses  104  and  106  being highly visible allows a service person or fitter of these valves to know if the valve cover  14 A has been appropriately tightened.  
         [0081]     If desired, as illustrated in  FIGS. 5 and 6 , an aperture  110  can be provided through the extension  100  in the vicinity of face  104  and an aperture  112  can be provided in the extension  102  in the vicinity of protruding boss  106 , so that once the face  104  and boss  106  are contacting (as in  FIG. 6 ) the apertures  110  and  112  are in alignment. This allows a pin, or a cable tie or other locking apparatus to be threaded through apertures  110  and  112  and secured to prevent the cover  14 A from unwinding from the valve body  10 A unintentionally. To an extent it also ensures that the valve has not been tampered with since the last servicing. The latter especially is possible if the locking means is of the sort that needs to be destroyed to be removed such as a cable tie or a frangible pin.  
         [0082]     In the embodiment of  FIGS. 5 and 6  the face  104  and boss  106  are provided in an offset location comppared to the circumference of the cover  14 A. If desired similar bosses can be provided within the circumference of the body  10 A, however to do this may require the wall thickness  115  (see  FIG. 5 ) to be increased in order to allow sufficient bearing area of face  104  and boss  106  and to allow for some locking mechanism if desired.  
         [0083]     It can be seen in  FIG. 5  that the threads  50 A and  48 A have axially extending grooves  120  and  122  on the body  10 A and grooves  124  on the cover  14 A. The grooves  120 ,  122  and  124  ensure that once the cover  14 A is unscrewed relative to the body  10 A and the underneath flange  130  of the cover  14 A breaks contact with an O-ring seal (not illustrated) situated on top of rim  132 , any gas pressure inside the valve body  10 A will be exhausted through the grooves  120 ,  122  and  124 . Clearly, the grooves need only be formed on any one of the valve body  10 A or cover  14 A, however, if desired, they can be located on both as is illustrated in  FIG. 5 . It is will be readily understood that this feature of one or more grooves  120 ,  122  or  124  is a desirable safety feature, and need not be present for the working of the valve.  
         [0084]     Illustrated in  FIGS. 7 and 7 A is a valve construction similar to that of  FIGS. 3 and 4 , with a cover arrangement similar to  FIGS. 5 and 6 . In  FIG. 7  like parts to those of previous Figures have been like numbered, and their function and purpose need not be described further. As can be seen from  FIG. 7  the flow control valve  2 B has a valve cover  14 A, O ring seal  130 , spring  28  and diaphragm  16 . The body  10 A has inlet and outlet male threaded connections  54  which cooperate with frusto-conical seals  54 A and gland nuts  54 B which together form a sealed connection with a conduit passing through them once gland nut  54 B is secured to threads  54  thus compressing the seals  54 A to seal against outer surface of the conduit.  
         [0085]     Illustrated in  FIG. 7  is a pin  112 A which is sized to fit through circular apertures  110  and  112  in the cover and body respectively when the cover  14 A is screwed onto the body  10 A and the apertures  110  and  112  are aligned.  
         [0086]     This alignment is assured due the arrangement of the threads  50 A and  48 A, and the cooperative interaction of boss  106  and shoulder  104  which engage each other preventing further tightening of the cover  14 A on body  10 A as described in relation to  FIGS. 5 and 6 .  
         [0087]     As illustrated in  FIG. 7A  the valve body  10 A includes an extension  100  similar in purpose to the extension  100  of  FIG. 5 . except that the extension  100  of  FIG. 7A  is of a shape which allows the valve body  10 A to have an axis of symmetry on either side of a plane AA which passes through the inlet, the outlet and bowl portion. The boss  106  also has a shape allowing it to be readily die cast. The boss  106  is sized relative to the threads  48 A and  50 A and the face  104  so as to function in the same manner as boss  106  of  FIGS. 5 and 6 . Turning now to  FIG. 8  there is disclosed a valve operator  200  for use with the covers of  FIGS. 5 and 6 .  
         [0088]     The operator  200  has a base  202  which can be made from a plastics material or alternatively manufactured from any suitable material such as steel, brass, aluminium, etc. If a plastics material is desired, preferably nylon  6  or glass filled nylon is utilised. However, if the operator  200  is to be used in a high temperature environment, the base  202  may need to be made of a material of better heat resistance than plastics and thus a metal or other heat resistant material will be more appropriate.  
         [0089]     The base  202  has a generally planar undersurface  204  to provide a sealing surface in conjunction with an o-ring (not illustrated) which would be positioned inside a groove  140  as illustrated in  FIG. 5, 6  or  7 .  
         [0090]     When used with the embodiment illustrated in FIGS.  5  to  7  the connecting means between the base  202  and the cover  14 A or  14 B is by means of a threaded tubular portion (not illustrated in  FIG. 8  but see similar feature being item  410  in  FIGS. 9 and 10 ) which extends downwardly from base  202  and engages the threaded port  142  in covers  14 A of  FIGS. 5 and 6 . This is a preferred arrangement and other mechanisms could be used to connect the base  202  to the port  142  in a sealed arrangement. Such other mechanisms can include bayonet fittings; providing the base  202  with a female thread to engage a male threaded portion surrounding the port  142 ; or other appropriate arrangement can be used.  
         [0091]     The base  202  as illustrated in  FIG. 8  includes an upwardly extending circumferential skirt  206  which serves the purpose of surrounding the base of a silencer  208  when located on the base  202 . Skirt  206  is optional and is provided in this embodiment mainly for aesthetic reasons. If desired, the base  202  can be made from a simple plate construction (that is without skirt  206 ) having an upper and lower generally planar surface (see base  202 A in  FIGS. 9 and 10 ).  
         [0092]     In the centre of the base  202  in  FIG. 8  is a valve seat  210  having a generally conical shape and providing a port  212  which can be sealed by means of a valve member  214  at the base of a plunger  216 .  
         [0093]     Upwardly extending from the base  202  are four support walls  218  which have spaces  220  between respective support members  218 . The spaces  220 , when the operator  200  is assembled, effectively form exhaust ports so that any air passing through the valve seat  210  when the valve member  214  is not engaging the valve seat  210 , will pass through the port  212  and out to atmosphere via the spaces  220 .  
         [0094]     The valve stem  216  is concentrically held over the valve seat  210  by means of a ferrule tube  222 . The ferrule tube  222  is assembled to the base  202  by first inserting the compression spring  224  and the plunger  216  coaxially adjacent thereto. The ferrule tube  222  is then pushed into connection with the base  202 , so that the rim of the base  226  of ferrule tube  224  when pushed towards base  202 , engages the angular surfaces  219  of each member  218 , thereby pushing the members  218  radially outward from the central axis of the base  202 . The members  218  continue to move outward until the base  226  of the ferrule tube  222  is located within a groove  230  which holds the base  226  and prevents it from moving either towards or away from the base  202 .  
         [0095]     Once the base  226  of the ferrule tube  222  is located in line with the groove  230  on each member  218 , the members  218 , by their relatively elastic nature, move radially inward relative to the central axis of the base  202 , thus locking ferrule tube  222  in position. The groove  230  and support members  218  keep the base  222  from moving relative to the seat  210  in any direction, ensuring that the ferrule tube  222  will apply an appropriate spring tension by means of spring  224  to force the plunger  216  to the closed position against the expected pressure which can be applied by gas pressure within the valve body, which bears against valve member  214  via port  212 .  
         [0096]     The operator  200  has its valve seat  210  normally closed due to the compression of spring  224 . A solenoid or coil (not illustrated) when activated, will pull the plunger  216  away from seat  210  against the bias of spring  224 . The ferrule tube  222  is received in the solenoid, which is secured to the ferrule tube  222  by means of a circlip (not illustrated) around the groove  232  in the iron top and shading ring  232 A.  
         [0097]     The silencer  208  is a ring of porous plastic or could be of some other porous material such as sintered bronze which would be particularly useful in high temperature environments. The silencer  208  is an optional feature of the operator  200  as the silencer  208  is not required for the operation of the operator  200 . However, with current noise abatement regulations and occupational health standards, the silencer  208  can be applied to the operator  200  by simply concentrically locating the silencer  208  around the outside surfaces of each of the support members  218  and locating the lower portion  240  of silencer  208  inside the annular space located between the outwardly facing side of support members  218  and the inwardly facing surface of annular skirt  206 .  
         [0098]     If desired, the lower portion  240  of silencer  208  can have a male thread formed thereon, with a female thread being formed on the inwardly facing surface of skirt  206 . If such threads were provided in portion  240 , then the silencer  208  could be screwed into the base  202  by means of threads on annular skirt  206  and lower portion  240 . This will permit the silencer  208  to have a tapered inner surface  242  so that as the silencer  208  is screwed into the base  202 , the surface  242 , if tapered, will force the support members  218  towards the central axis of the base  202 . This will positively urge the support members  218  towards the centre of the base thus securing the ferrule tube  222  into the annular groove  230 . Even without such threading and tapering, the silencer  208  helps to prevent the support members  218  from moving in a radially outwardly direction thus preventing them from disengaging from the base  226  on ferrule tube  222 .  
         [0099]     In another embodiment, an operator  400  is illustrated in  FIGS. 9 and 10 . Like parts of the embodiment of  FIGS. 9 and 10  compared to  FIG. 8 , have been like numbered and their function need not be repeated, as reference can be had to the previous description. In this embodiment the operator  400  is formed with a base  202 A which interconnects, without means of a ferrule tube, to a solenoid body  401 . That is the base  202 A and the solenoid body  401  alone provide the means to slidably retain the plunger  216 A in position and permit it only to move in an axial direction towards and away from the valve seat  210 A. In this embodiment an iron top and shading ring  401 A is provided within the solenoid body  401 .  
         [0100]     Four support members  218 A terminate in a barb formation  402  so as to engage flange  403  formed with or attached to the casing of solenoid body  401 . The operator  400  of  FIGS. 9 and 10  has like parts to the valve  200  of  FIG. 8 . These like parts are like numbered and end with the letter “A”.  
         [0101]     In  FIGS. 9 and 10 , there can be seen the threaded tubular spigot  410  (not illustrated in  FIG. 8 ) which allows for threaded attachment to the threaded port  142  of FIGS.  5  to  7 .  
         [0102]     Illustrated in FIGS.  15  to  18  is another operator  400 A similar to that illustrated in  FIGS. 9 and 10 . Like parts in FIGS.  15  to  18  when compared to FIGS.  8  to  10  have been like numbered, and further description of their function is not required as reference can be had to the previous description.  
         [0103]     The operator  400 A includes a solenoid body  401  which has four equi-spaced retaining formations  403 A which extend radially away from a cylindrical portion  403 B at the base of the solenoid body  401 . Each retaining formation  403 A includes a groove  403 C and an tapered lower extremity, the purpose of each these be described later.  
         [0104]     The support walls  218 A are similar to those in  FIGS. 9 and 10 , except that a barb like structure  402 A is outwardly directed and the four equi-spaced support walls  218 A are of a width to fit into the spaces between the retaining formations  403 A.  
         [0105]     A retaining ring  500 , such as circlip, cable tie, twisted wire or other appropriate retainer can be used to retain all the components securely together as illustrated in  FIG. 16 . As can be seen in  FIG. 16 , when assembled, the support walls  218 A fit between the retaining formations  403 A until the lowermost part of the barb  402 A is at the upper most wall or part of the groove  403 C. Once in this position the circlip  500  can be positioned in the groove  403 C thus keeping all the components locked together. The tapered lower extremity of the retaining formations  403 A aid in the positioning of the circlip  500 , by allowing the circlip  500  to be expanded due to it being pushed along the tapered extremity in the divergent direction. Once circlip  500  is aligned with groove  403 C, the circlip will enter the groove  403 C and trap the barb  402 C into the position illustrated in  FIG. 16 .  
         [0106]     As can be seen in  FIGS. 17 and 18  when the operator  400 A is closed the spring  224 A biases the plunger  216 A to the closed position sealing the valve seat  210 A and port  212 A. When the solenoid in solenoid body  401  is activated as in  FIG. 18 , the plunger  216 A is retracted compressing the spring  224 A between the plunger  216 A and iron top and shading ring  401 A, thereby opening the port  212 A to atmosphere. This allows air to escape through spaces  220 A (see  FIG. 16 ) between the support walls  218 A and underneath the retaining formations  403 A, thereby forcing the diaphragm to move the valve seat in the valve body to the open position.  
         [0107]     Illustrated in FIGS.  11  through to  14  is an alternative mechanism to lock the cover  14 C on to a valve body  10 C when the valve body  10 C is under pressure. The arrangement can be seen more clearly in  FIG. 14  whereby a spring biased pawl  310  is situated in a cylinder  312  located in the valve body  10 C. As can be seen from  FIG. 10 , the cylinder  312  is located offset from the circumference of the cover  14 C.  
         [0108]     As is illustrated in  FIG. 12 , the cover  14 C operates in a similar fashion to that of FIGS.  5  to  7  in that a protruding boss is provided on the cover  14 C which engages a protruding boss or protrusion  316  on body  10 C.  
         [0109]     The cylinder  312  is connected by a passage  318  to the main volume of the valve body  10 C. The cover  14 C will be correctly positioned onto the valve body  10 C, once the cover  14 C is correctly tightened, that is when protruding boss  314  engages protrusion  316 . When boss  314  and protrusion  316  engage, this will cause an alignment of aperture  320  over pawl  310 . When the aperture  320  is directly above the pawl  310  and pressure is applied to the valve body  10 C, air travelling through passage  318  gains access to the cylinder  312  thereby forcing the pawl  310  against the bias of compression spring  322  through the aperture  320  in cover  14 C. Thus the cover  14 C cannot be released until such time as pressure is released from the valve body  10 C. Once pressure is released, the compression spring  322  will force the pawl  310  back into cylinder  312 , thus allowing the cover  14 C to be removed from the body  10 C.  
         [0110]     Clearly, many variations may be made to the above described embodiments without departing from the scope of the invention. The embodiment shown in  FIGS. 3 and 4  depicts an arrangement in which the inlet and outlet have external threads  54  thereon to allow for a different type of connection arrangement to the air conduits. However, the arrangement shown in  FIGS. 3 and 4  employ the same valve seat configuration which, it will be noted from  FIG. 4 , is located below the upper edge  46  of the inlet.  
         [0111]     It will be understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.