Patent Publication Number: US-2022227035-A1

Title: Directional Control Valve and a Sealing Arrangement Therefore

Description:
This invention relates to directional control valves and sealing arrangements for spool valves. 
     Directional control valves, such as spool valves, are used in hydraulic and pneumatic machinery to restrict, permit, or change direction of flow from a pressurised source. Typically, spool valves are classified in accordance with the number of ports, number of spool positions, actuation methods, and type of spool. 
     In a known configuration, a spool valve comprises a housing with a bore and a sliding spool disposed within the bore. The bore may include a plurality of grooves for receiving o-rings. The o-rings are seated in the grooves and are slideably engaging the bore, thus defining and separating adjacent fluid chambers. Appropriate sealing is crucial from the perspective of correct operation of the spool valve, as adjacent fluid chambers may sometimes be at significantly different pressures. 
     Using o-rings in a spool valve has various disadvantages. In applications such as stretch blow moulding, actuation speed, thus opening and closing time, must be carefully controlled. Upon actuating the valve, o-rings interact with the bore of the housing to create a frictional force opposing the actuation force. Therefore, achieving a specific actuation speed and time may not be always possible, as it is dependent upon the extent of this frictional interaction. 
     Secondly, installation and maintenance of such seals is challenging. The diameter of a typical groove for receiving seals is larger than the diameter of the seal. Dedicated tooling is required to place the seal within its groove. Installation of the seal involves stretching the seal using dedicated tooling, arranging the seal around its respective groove, and removing the tool to allow the seal to drop into the groove. The installation process may scratch or even break the seal. Removing spent or damaged seals is also done using dedicated tools, such as a pick tool. The sharp end of the pick tool is used to pry off the seal from its respective groove. Rubber o-rings removed in this fashion cannot be re-used, as they usually get irreversibly damaged in the process. Moreover, frequent seal changes can lead to scratching of the surface of the spool, which may reduce the efficiency of operation of the valve. 
     The object of the present invention is to provide an improved valve, which addresses at least one of the abovementioned problems. 
     Thus, according to a first aspect of the invention there is provided a valve comprising a bore extending about an actuation axis, an inlet port, a first outlet port, a first exhaust port, a second outlet port, and a second exhaust port, wherein a spool inside the bore is actuated between a first working position and a second working position, and a first circumferential seal wing and a second circumferential seal wing being arranged on the spool,
         wherein a diameter of the spool is smaller than a diameter of the bore thus establishing a first fluid path between the inlet port and the first outlet port, establishing a second fluid path between the first outlet port and the first exhaust port, establishing a third flow path between the inlet port and the second outlet port, and establishing a fourth flow path between the second outlet port and the second exhaust port;   a first annular recess radially extending from the bore and being in permanent fluid communication with the first outlet port, the first annular recess comprising an outer first recess wall next to the first exhaust port and an inner first recess wall next to the inlet port;   a second annular recess radially extending from the bore and being in permanent fluid communication with the second outlet port, the second annular recess comprising an outer second recess wall next to the second exhaust port and an inner second recess wall next to the inlet port,       

     whereby the first seal wing and the second seal wing are arranged on the spool, such that:
         in the first working position, the first seal wing abuts to the outer first recess wall, thus closing the second fluid path and opening the first fluid path, and the second seal wing abuts to the inner second recess wall, thus closing the fourth flow path and opening the third flow path;   in the second working position, the first seal wing abuts to the inner first recess wall, thus closing the first flow path and opening the second fluid path, and the second seal wing abuts to the outer second recess wall, thus closing the third flow path and opening the third flow path.       

     Advantageously, arranging seals in this way minimises frictional interaction between the seals and the bore. This accounts for much faster switching times of the valve. The switching times can also be accurately controlled, as there are almost no frictional losses in this system. Whilst achieving all of the above, the seals are able to separate chambers under vastly different pressures. This arrangement improves durability of the valve, as the seals wear out slower. It also has a positive effect on running costs and downtime. 
     Lastly, the seals can abut the housing, instead of rubbing against it, which further improves their durability. 
     Optionally, the valve includes a housing, a first cap, and a second cap, the housing having the bore, and having a first housing end and a second housing end, wherein the first cap is disposed at the first end of the housing, and the second cap disposed at the second end of the housing, the valve further comprising a biasing element for returning the valve from the second working position to the first working position and disposed around the spool and between the spool and the second cap. 
     Optionally, the first seal wing is flexible, such that, in the first working position of the valve, it is adapted to abut the first outer recess wall so as to elastically deflect, and wherein the second seal wing is flexible, such that, in the second working position of the valve, it is adapted to abut the second outer recess wall so as to elastically deflect. 
     Advantageously, elastic deflection of each seal wing eliminates the need for frictional interaction between the bore and each seal wing. Instead, sealing between neighbouring fluid chambers is possible due to a wing pressing against the respective wall of the respective recess. This provides the necessary sealing between two pressurised 
     Optionally, the valve comprises a tubular connector disposed around the spool and extending axially between the first and second seal wing, wherein the first seal wing, the second seal wing, and the tubular connector together form a unitary seal. 
     Advantageously, two wings and a tubular connector form a unitary seal. The unitary seal is a single component, making it easy to manufacture. Its shape facilitates quick and simple assembly on the spool. Cost of production and time to assemble are both substantially reduced. 
     Optionally, the valve further comprises a first dynamic seal and a second dynamic seal, said first and second dynamic seal being circumferentially disposed around each end of the spool, the dynamic seals being configured to centre the spool such that the spool does not directly contact the bore of the housing. 
     Advantageously, dynamic seals are the only component which is in continuous contact with both the spool and the bore. Owing to that, the spool is moveable within the bore with a minimal amount of friction. Friction in the system is only due to the dynamic seals moving along the surface of the bore. 
     Optionally, the second pressure cap comprises a secondary bore for receiving the spool, wherein the secondary bore is permanently fluidly connected to the second annular recess, such that the secondary bore is configured to act as an air spring for transmitting the spool from the second working position to the first working position, wherein the first dynamic seal is arranged between the bore and the spool and the second dynamic seal is arranged between the spool and the secondary bore. 
     Advantageously, the air spring uses the pressure of the main pressure supply to create a cushion of pressurised air which helps to move the spool from a working to a resting position. The air spring helps achieve faster switching times, thus directly increasing throughput of a blow moulding machine, for instance. 
     Optionally, the valve further comprises a first chamfered edge disposed at an intersection between the bore and the inner first recess wall, and comprising a second chamfered edge disposed at an intersection between the bore and the inner second recess wall. 
     Optionally, the spool includes a first radially extending protrusion for accommodating the first seal wing, and wherein the spool includes a second radially extending protrusion for accommodating the second seal wing. 
     Advantageously, wings of the seal are supported by respective protrusions, thereby preventing plastic deformation of the wings when engaging one of the recesses. 
     Optionally, the first seal wing has a diameter which is smaller than a diameter of the first recess, and wherein the second seal wing has a diameter which is smaller than a diameter of the second recess. 
     Advantageously, each seal wing interacts only with radial walls of its respective recess and does not touch circumferential walls of its respective recess. This reduces losses due to friction and increases a lifetime of each seal wing. 
     Optionally, in the second working position, the first sealing wing is sheared between the first chamfered edge of the first recess and the first protrusion so as to establish a fluid tight contact patch therebetween, while the second seal wing bears against the outer second recess wall, so as to deflect from the second protrusion, forming a gap therebetween, and wherein, in the first working position, the second sealing wing is sheared between the second chamfered edge of the second recess and the second protrusion so as to establish a fluid tight contact patch therebetween, while the first seal wing bears against the outer first recess wall, so as to deflect from the first protrusion, forming a gap therebetween. 
     Advantageously, each seal wing is clamped between a protrusion and a chamfered edge. Because these two components are at a substantially similar angle with respect to a horizontal plane, each wing can be sheared between the protrusion and the chamfered edge. This increases the contact patch between the seal wing and the protrusion, as well as the protrusion and the chamfered edge, to provide improved sealing between neighbouring zones under varying pressures. 
     Optionally, the valve further comprises an actuator operatively connected to the spool for moving the spool from the first working position to the second working position, where the actuator is: electromechanical, hydraulic, or pneumatic, wherein the actuator is disposed on or within the first cap. 
     Advantageously, the valve assembly is not limited to one actuation method, as it may be actuated using various available methods. 
     Optionally, the spool comprises of a first module and a second module, wherein the second module receives the first module thus forming an interference fit therebetween, and wherein the first module includes the first radially extending protrusion, and wherein the second module includes the second radially extending protrusion, and wherein the biasing element is clamped between the second protrusion and the second pressure cap. 
     Advantageously, the modular construction of the spool facilitates easy assembly of various elements of the valve, in particular the biasing spring and the unitary seal. 
     According to a second aspect of the present invention there is provided a blow moulding machine, comprising: 
     a main valve comprising a housing and a piston moveable within the housing, the housing having at least one inlet port and at least one outlet port in fluid communication with the inlet port, the housing also comprising a first control port and a second control port, the first control port being in fluid communication with a first control chamber and the second fluid port being in fluid communication with the second control chamber, a valve as defined in of any of the preceding claims, wherein the first outlet port is in fluid communication with the first control port, and the second outlet port is in fluid communication with the second control port, such that when the valve is in the open position, the piston opens a flow path between the inlet port and the outlet port, and when the valve is in the closed position, the piston closes the flow path between the inlet port and the outlet port. 
     Optionally, the main valve is pressure balanced, or wherein the blow moulding valve is for manufacturing plastic containers, or plastic bottles. 
     Advantageously, using the above described valve in a blow moulding machine will significantly increase throughput of such a machine, with no effect on quality of produced bottles. Faster switching times, lower failure frequency and easy assembly have a positive effect on reliability, speed of operation and reparability. 
     According to a third aspect of the present invention there is provided a seal, comprising: a tubular section extending along an axis and having a first and a second end; 
     a first wing section disposed at the first end of the tubular section, the first wing section extending radially away from the first end of the tubular section; 
     a second wing section disposed at the second end of the tubular section, the second wing section extending radially away from the second end of the tubular section; 
     wherein the first wing section and the second wing section extend axially along the axis away from one another, wherein the tubular section, the first wing section, and the second wing section together define a unitary seal for a spool valve. 
     Advantageously, a unitary seal is relatively simple to mass produce using known manufacturing techniques. 
     According to a fourth aspect of the present invention there is provided a method of assembling a valve of any preceding claim, comprising the steps of:
         providing: a housing having a bore extending along an axis, and having a first end and a second end; a modular piston having a first module and a second module, wherein the first module is received in an opening of the second module, the first module having a first radial protrusion and the second module having a second protrusion; a unitary seal having a tubular section with a first and a second end; a biasing spring; a pressure cap;   providing a tubular insert for introducing the unitary seal into the bore of the housing, the tubular insert being smaller than the bore and having an inner surface for engaging with the unitary seal;   compressing radially the unitary seal and subsequently inserting the compressed unitary seal into the tubular insert;   inserting the first module of the piston into the housing;   inserting the tubular insert with the compressed unitary seal into the housing and mounting the tubular section of the unitary seal on the first module of the piston so that the unitary seal is in contact with the first radial protrusion;   assembling the second module onto the first module so that the seal is also in contact with the second radial protrusion;   attaching the first pressure cap to the first housing end;   disposing the biasing spring on the second radial protrusion;   attaching the pressure cap to the second housing end, such that the spring is clamped between the second protrusion and the second pressure cap.       

     Advantageously, the above method facilitates mounting a unitary seal on a spool with a relative ease. The method ensures that the seal remains intact after assembly. Moreover, the method does not require stretching of the seal or aligning of the seal with its respective groove. This results in shorter overall downtime, as seals do not have to be replaced frequently. 
    
    
     
         FIG. 1  is an isometric view of the valve assembly of the first embodiment of the invention 
         FIG. 2  is a section view of the valve assembly of  FIG. 1  in a closed position 
         FIG. 3  is a close up view of detail A-A 
         FIG. 4  is a section view of the valve assembly of  FIG. 2  in an open position 
         FIG. 5  is a close up view of detail B-B 
         FIG. 6  is a section view of the actuator of the valve assembly in accordance with the first embodiment of the invention 
         FIG. 7  is a schematic view of a blow moulding machine 
         FIG. 8  is a section view of a second embodiment of the invention in a closed position 
         FIG. 9  is a section view of a second embodiment of the invention in an open position 
         FIG. 10  is a section view of a third embodiment of the invention in an open position 
         FIGS. 11 a - c    are an isometric view of the steps required to insert a seal into the valve in accordance with any of the embodiments 
         FIG. 12 a    is a partial section view of the valve with a partially inserted seal 
         FIG. 12 b    is a partial section view of the valve with an almost fully inserted seal 
     
    
    
     VALVE ASSEMBLY 
     A first embodiment of a valve assembly  10  is shown in  FIG. 1 . The valve assembly  10  comprises a housing  12 , a first cap  16 , a second cap  18 , and an actuator  17 . 
     As shown in  FIGS. 2 and 4 , the valve assembly  10  further comprises a spool  34 , a seal  54 , and a spring  38 . 
     The housing  12  of the valve assembly  10  includes a bore  14 . The bore  14  extends along the housing  12  and defines an actuation axis A. The housing  14  has two axially opposing and distal ends—a first end  12 A and a second end  12 B. The bore  34  also defines a space for receiving the spool  34 . The bore  34  may be circular, although the cross sectional shape of the bore  34  depends on the desired shape of the spool  34  to be used in the valve assembly  10 . In the first embodiment, the spool  34  is substantially cylindrical and slideably engages a substantially cylindrical interior surface of the bore  14 . 
     In the embodiments shown in  FIGS. 2 and 4 , the valve assembly  10  is a 5/2 valve, however any other suitable arrangement, such as a 3/2 or a 4/2 valve, is also possible. It is known that the 5/2 valve is characterised in that it includes five ports and has two possible spool positions. The spool  34  is therefore moveable between a closed position located at the first end  12 A and an open position located at the second end  12 B. “Open position” and “closed position” make reference to the operating mode of the first fluid path. 
     As shown in  FIGS. 3 and 5 , the housing  12  also includes a first recess  22 A and a second recess  22 B. The first recess  22 A extends radially away from the bore  14  and into the housing  12  and forms a groove of a predetermined axial thickness and radial depth. The first recess  22 A is circumferentially disposed around the spool  34 . The first recess  22 A has an outer wall  24   a  which is aligned with a plane parallel to the first end  12 A of the housing  12  and an inner wall  24   b  opposite to the outer wall  24   a . The first recess  22 A also includes a first chamfer  26 A which is disposed at an intersection of an inner wall  24   b  of the first recess  22 A and the bore  14  and which lies opposite to the outer wall  24   a.    
     The second recess  22 B is substantially a mirror image of the first recess  22 A. The second recess  22 B has an outer wall  24   d  which is aligned with a plane parallel to the second end  12 B of the housing  12  and being located closer to the second end  12 B that to the first end  12 A. The second recess  22 B also includes an inner wall  24   c , located opposite the outer wall  24   d . The second recess  22 B also includes a second chamfer  26 B which is disposed at an intersection of an inner wall  24   c  of the second recess  22 B and the bore  14  and lies opposite to the outer wall  24   d.    
     Referring again to  FIGS. 2 and 4 , the housing  12  of the valve assembly  10  has 5 primary ports—an inlet port  44 , a first outlet port  50 , a second outlet port  46 , a first exhaust port  52 , and a second exhaust port  48 . 
     The inlet port  44  is fluidly connected to a working pressure source, so as to supply working pressure to the valve assembly  10 . The first outlet port  50  and the second outlet port  46  are fluidly connectable to an external hydraulic/pneumatic device, for example to control an auxiliary valve assembly. The auxiliary valve assembly may be a valve, for example a pressure balanced valve. The valve assembly  10  can thus be used as one of the pilot valves in a complex pressure system, such as a stretch blow moulding machine. 
     The first exhaust port  52  and the second exhaust port  48  are connected either to the external atmosphere, or to a vacuum source, to remove pressurised fluid from the valve assembly  10 . In the embodiment shown in  FIGS. 2 and 4 , the primary ports are arranged substantially along the actuation axis A, although any other arrangement is possible, for example each port being arranged at a different circumferential or radial position with respect to the actuation axis A. In the embodiments of  FIGS. 3 and 4 , the primary ports are arranged in the following order (going from the second end  12 B to the first end  12 A of the housing  12 )—first exhaust port  52 , first outlet port  50 , inlet port  44 , second outlet port  46 , and second exhaust port  48 . The person skilled in the art would appreciate that the order in which the primary ports are arranged may be modified. 
     The second outlet port  46  is located on a radial wall of the second recess  22 B, while the first outlet port  50  is located on a radial wall of the first recess  22 A. 
     Referring again to  FIGS. 2 and 4 , the housing  12  also defines secondary fluid conduits. In the first embodiment of the invention, the housing  12  includes an air spring conduit  21  and an actuator supply conduit  23 A. The purpose of the air spring conduit  21  is to supply pressurised fluid from the working pressure supply to an air spring chamber  32 B of the second cap  16 . As shown in  FIG. 6 , the actuator supply conduit  23 A delivers working fluid from the working pressure supply to the actuator  17 . 
     Referring again to  FIGS. 2 and 4 , the second cap  16  is partially received within the bore  14  on the first end  12 A of the housing  12 . The first cap  18  is partially disposed within the bore  14  on the second end  12 B of the housing  12 , opposite the second cap  16 . The second cap  16  is thus longitudinally spaced along the actuation axis A from the first cap  18 . 
     In the first embodiment of the invention, the first cap  18  together with the housing  12  defines the actuator supply conduit  23 A to supply the working pressure to the actuator  17 . The first cap  18  also includes an actuator outlet conduit  23 B for inducing working pressure to the bore  14  of the housing  12  in order to move the spool  34  from the closed position to the open position. The first cap  18  also includes an actuator exhaust conduit  23 C for exhausting working fluid out of the actuator  17 . 
     All pressure interfaces between the housing  12  and the first cap  18  or the second cap  16  are fluid tight thanks to o-ring or any other suitable sealing means disposed between the housing  12  and the caps. 
     The actuator outlet conduit  23 B is in fluid communication with an actuator chamber  42  defined within the bore  14  and between the spool  34  and the first cap  18 . Pressure supplied via the actuator outlet conduit  23 B to the actuator chamber  42  is used to actuate the spool  34  from the closed position to the open position. 
     The air spring chamber  32 B of the second cap  16  is in fluid communication with the air spring conduit  21 , via which pressurised medium is delivered to the air spring chamber  32 B. The air spring chamber  32 B partially receives the spool  34 . The spring chamber  32 B also has a bore  32  that defines circumferential walls of the air spring chamber  32 B. 
     Referring to  FIGS. 2 and 4 , the seal  54  is disposed circumferentially around the spool  34  and extends along the longitudinal axis A. The seal  54  includes a first wing  56 A and a second wing  56 B, spaced axially apart from the first wing  56 A. The wings are interconnected by an annular central section  70  extending along the actuation axis A. The first wing  56 A extends radially from the central section  70  towards and into the first recess  22 A. Similarly, the second wing  56 B extends radially from the central section  70  towards and into the second recess  22 B. Each wing is angled away from the radial plane, towards the housing end the closest to it. Therefore, the first wing  56 A is angled towards the first end  12 A and the second wing  56 B is angled towards the second end  12 B. 
     As shown in  FIGS. 2 and 4 , the spool  34  is of a modular design and is comprised of a male module  34 A and a female module  34 B. The two modules may be connected together using interference fit, adhesive, or any other suitable assembly method. The male module  34 A is proximal to the first end  12 A whereas the female module  34 B is closer to the first end  12 B. Referring to  FIGS. 2 and 4 , the male module  34 A includes a radially extending and circumferentially disposed first projection  36 A for supporting the first wing  56 A. The second sealing wing  56 B is supported by a second projection  36 B, extending radially from and disposed circumferentially around the female module  34 B. Each projection is annular and substantially conical in cross-sectional view as shown in  FIGS. 2 and 4 , although other suitable shapes are also possible. In the first embodiment of the invention, the central section  70  of the seal  54  is disposed around the male module  34 A. A skilled person would appreciate that the male module may be a female module and vice versa. 
     The spool  34  includes a first end seal  40 A and a second end seal  40 B disposed around opposing ends of the spool  34 . The second end seal  40 B is seated on the male module  34 B of the spool  34  and is slideably in contact with the bore  14  of the housing  12 . The first end seal  40 A is seated on the female module  34 A and is slideably in contact with the bore  32 A of the air spring chamber  32 . These seals can be of any type, for example a double lip seal or o-ring. Therefore, at any spool  34  position, there is no metal on metal contact between the spool  34  and the bore  14 . 
     The valve  10  may also be part of a larger pressure system, for example a blow moulding machine  400 , as shown in  FIG. 7 . For illustrative purposes, the valve  10  was shown in  FIG. 7  in a simplified manner. In the system  400  the valve assembly  10  is used as a pilot valve. In such a machine, the valve  10  is fluidly connected to a main valve  410  comprising a housing  412  having a bore  414 , a piston  416  slideaby mounted within the bore  414  and moveable between an open position and a closed position. It is envisaged that the piston  416  is pressure compensated or a standard, not pressure compensated piston. The housing  412  defines a first control port in fluid communication with a first control chamber  418  and a second control port in fluid communication with a second control chamber  420 . The first control chamber  418  is in fluid communication with the second outlet port  46  of the valve  10  and the second control chamber  420  is in fluid communication with the first outlet port  50  of the valve  10 . The housing  412  further defines an inlet port  422  and an outlet port  424  and a flowpath between the inlet port  422  and the outlet port  424 . 
     The outlet  424  of the main valve  410  is fluidly connected to a moulding apparatus  430 . The moulding apparatus  430  includes a mould  426  and a preform  428 . The moulding apparatus  430  facilitates shaping the plastic preform  428  to the shape of the mould  426  under certain conditions, one of which being application of pressure to the moulding apparatus  430 . Due to being connected to the outlet  424  of the main valve  410 , the moulding apparatus  430  receives pressure sufficient to mould the preform  428  when the flowpath between the inlet  422  and the outlet  424  of the main valve  410  is open. The preform  428  can be made of any material suitable for blow moulding, for example PET, although any suitable type of plastics known to the skilled person is possible. 
     Valve assembly  10  is a pilot valve to the main valve  410 , meaning that any pressurised fluid flowing from the valve assembly  10  via the first outlet port  50  into the first control chamber  418  will result in the piston  416  moving along its actuation axis so as to close the flowpath between the inlet port  422  and the outlet port  424 . 
     In describing alternative embodiments, similar reference numbers are used for the same components. 
     A second embodiment of the invention is shown in  FIGS. 8 and 9 . The second embodiment of the valve assembly  110  is substantially the same as the first embodiment of the valve assembly  10 , except no air spring or radial seal at the second end  112 B are included. Such a valve assembly  110  is controlled by the pressure from the actuator supplied via the actuator outlet conduit  123 B into the actuator chamber  142 . 
     A third embodiment if the invention is shown in  FIG. 10 . The third embodiment is substantially the same as the second embodiment shown in  FIGS. 8 and 9 . The valve assembly  210  of the third embodiment differs in that the actuation method is purely mechanical. A plunger  280  is operatively connected to the spool  234  at the first end  212 A of the housing  212 . The plunger  280  is colinear with the spool  234 . Actuation of the valve assembly  210  is therefore facilitated by pushing the plunger into the spool  234 . 
     It is envisaged that any of the embodiments described above could form part of the blow moulding system  400  and serve as pilot valves connected to the main valve  410 . 
     Assembly of the Seal 
     Referring to  FIGS. 11 a  to 11 c   , the seal  54  is of a unitary construction, meaning that assembling the seal  54  requires additional tooling, so as to place the seal  54  in position within the housing  12  without the risk of damaging the seal. Advantageously, the seal  54  can be inserted into the housing  12  by means of an inserting means  60 . The inserting means  60  comprises an exterior section  62  including an outside insert surface  62 A and an inside insert surface  62 B, and a bore section  64 . The exterior section  62  defines an opening  66  through which the seal  54  can be inserted into the inserting means  60 . The exterior section  62  also includes an outer surface  62 A and an inner surface  62 B, both of which are circumferentially disposed around a longitudinal axis of the inserting means  60 . The interior section  64  extends longitudinally from the exterior section and has a diameter which is smaller than the diameter of the bore  12 , to the extent that the interior section  64  can be inserted into the bore  12 . The interior section  64  is, in fact, the only part of the inserting means  60  which may enter the bore  12 . The exterior section  62  abuts an outside surface of the housing  12  such that the exterior section  62  does not enter the bore  14  when the insert  60  is inside the housing  12 . The exterior section  62  also defines a chamfered lip  62 C and the inside surface  62 B is tapered. 
     In use, as shown in  FIG. 11 c   , the seal  54  is inserted into the inserting means  60  through the opening  66 . To insert the seal  54  fully into the bore section  64 , the seal  54  must first be forced through the exterior section  62  with help of a lubricant. Referring now to  FIGS. 12 a  and 12 b   , firstly, the first module  34 A of the spool  34  is inserted into the bore  14  of the housing  12 . The exterior section  62  fits around the first module  34 A of the spool  34 . Forcing the seal  54  through the inserting means  60  is achieved by installation means  67  which installation means  67  enables to force the seal  54  across the inserting means  60  so as to locate the seal  54  within the recesses of the valve assembly  10 . The lip  66 C and the inside surface  62 B help to gradually compress the seal  54  before it enters the bore section  64 . Seal  54  with compressed first seal wing  56 A and compressed second seal wing  56 B is then forced along the inserting means  60  by installation means  67 , onto the first module  34 A of the spool  34 . The exterior section  62  acts as a positive stop and the length of the bore section  64  is such that, when fully within the bore  14 , the inserting means  60  terminates before the inside wall  24   b  of the first recess  22 A. The inserting means  60  is then removed from the bore, all the while holding the seal  54  in place by means of the installation means  67 , in order to enable seal wings to expand. Firstly, the first seal wing  56 A expands into the first recess  22 A and then the second seal wing  56 B expands into the second recess  22 B. Once the inserting means  60  is fully removed, the seal  54  expands into its design shape. Once the seal  54  expands into its design shape, the second module  34 B is inserted, so as to axially constrain the seal  54 . After that, caps can be attached to each ends of the housing  12 , so as to create a fluid tight environment within the valve assembly  10 . Advantageously, the seal  54  can be inserted into the bore  14  which has multiple sharp edges without compromising its structural integrity or surface quality. 
     Operating Principles 
     Sealing Element 
     I. Closed Position 
     In use, the spool  34  is moveable between a closed position and an open position. In the closed position, the male module  34 A of the spool  34  is at its top dead centre in the proximity of the first end  12 A. This arrangement is illustrated in  FIG. 2 . The closed position in the sense of this embodiment means that pressurised fluid enters the system via the inlet port  44 , the first outlet port  50  is pressurised, the actuator supply conduit  23 A is pressurised, and the actuator  17  is switched off. Thus, there is a flow path established between the first outlet port  50  and the inlet port  44 , with all other primary ports not being fluidly connected to the working pressure source. 
     In such conditions, as shown in  FIG. 3 , the second wing  56 B abuts against the inner wall  24   c  of the second annular recess  22 B, while he first wing  56 A bears against the outer wall  24   a  of the first annular recess  22 A. More specifically, the second wing  56 B abuts the chamfered edge  26 B of the second recess  22 B such that the second wing  56 B is sheared between the second projection  36 B and the chamfered edge  26 B. The first wing  56 A is lifted off the first projection  36 A, meaning that the relative angle between the body of the first wing  56 A and a radial plane is smaller than in a neutral position, whereby the second wing  56 B rests on the second projection  36 B. The deflection of the first wing  56 A is balanced by the net force applied to the first wing  56 A by the working pressure from the inlet port  44 . Therefore, the seal  54  separates areas of high and low pressure from each other, wherein high pressure fluid always acts on the surface of the seal  54  angled towards the inside surface of the bore  14 . 
     In the closed position, the seal  54  prevents pressurised fluid from entering the second outlet port  46 , the second exhaust port  48 , the second exhaust port  48 , or the air spring conduit  21 . Therefore, the first seal wing  56 A and the second wing  56 B work together to maintain a flow path between the inlet port  44  and the first outlet port  50 . In the open position, the spring  38  is decompressed and the air spring chamber  32  contains fluid at low pressure or vacuum. Therefore, the valve assembly  10  will remain in this position, unless the actuator  17  actuates the spool  34 . 
     In relation to the blow moulding system  400  of  FIG. 7 , when the valve assembly  10  is in the closed position, working fluid is expelled from the valve assembly  10  via the first outlet port  50  into the first control chamber  418  of the main valve  410 . At the same time, there is no working pressure in the second outlet port  46  which is connected to the second control chamber  420 . The net force on the piston  416  is such that the flowpath between the inlet port  422  and the outlet  424  is closed by the piston  416 . In this position, no pressurised fluid is induced into the moulding apparatus  430 . Therefore, no blow moulding is actively taking place. This moment of inactivity may be used to prepare the moulding apparatus  430  for moulding a bottle, for example by inserting a preform  428  into the mould  426  and establishing a fluid communication channel between the blow moulding apparatus  430  and the main valve  410 . 
     As regarding the second embodiment of the invention shown in  FIGS. 8 and 9 , maintaining the valve assembly  110  in the closed position is achieved using similar means as those described above in relation to the first embodiment of the valve assembly  10 . The seal  154  abuts walls of relevant recesses  122 A and  122 B at the same locations and in a similar fashion to the first embodiment. The main difference being that the second embodiment has no air spring channel, so no vacuum or low pressure is maintained in such a channel. This valve assembly  110  may also achieve closing of the flowpath of the main vale  410 , thus preventing any fluid from entering the blow moulding apparatus  430 . 
     Regarding the third embodiment of the invention shown in  FIG. 10 , the seal  254  of the valve assembly  210  operates in a similar way to that described in relation to the first and second embodiment. The difference between the valve assembly  210  and the valve assembly  10  is that channels for delivering working fluid to the air spring or to and from the actuator are not present in the valve assembly  210 . Actuation is purely mechanical, achieved by means of the plunger  280 . In the closed position, the plunger  280  does not apply any axial forces onto the spool  234 , thus enabling a flowpath between the inlet port  244  and the first outlet port  250 , with the first exhaust port  252 , the second outlet port  246  and the second exhaust port  248  not fluidly connected to a pressure supply. 
     II. Open Position 
     In the first embodiment, the female module  34 B of the spool  34  is at its top dead centre in the proximity of the first end  12 B when the spool is in the open position. This arrangement is illustrated in  FIG. 4 . The open position means that the pressurised working fluid enters the system via the inlet port  44  and there is an open flowpath between the inlet port  44  and the second outlet port  46 . In such a case, the actuator  17  is switched on, meaning it opens a flowpath going from the inlet port  44 , via the actuator supply conduit  23 A onto the actuator outlet conduit  23 B and into the actuator chamber  42 . Therefore, the actuator  17  overcomes the biasing force of the biasing force of the spring  38 , moving the spool  34  and compressing the spring  38 . 
     In such conditions, as shown in  FIG. 5  the first wing  56 A abuts against the inner wall  24   b  of the first annular recess  22 A, while the second wing  56 B bears against the outer wall  24   d  of the second annular recess  22 B. More specifically, the first wing  56 A abuts the chamfered edge  26 A of the first recess  22 A such that the first wing  56 A is sheared between the first projection  36 A and the chamfered edge  26 A. The second wing  56 B is lifted off the second projection  36 B, meaning that the relative angle between the body of the second wing  56 B and a radial plane is smaller than in a neutral position, whereby the second wing  56 B rests on the radial projection  36 B. The deflection of the second wing  56 B is balanced by the net force applied to the second wing  56 B by the working pressure from the inlet port  44 . Therefore, the seal  54  separates areas of high and low pressure from each other, wherein high pressure fluid always acts on the surface of the seal  54  angled towards the inside surface of the bore  14 . 
     In the open position, the seal  54  prevents pressurised fluid from entering the first outlet port  50 , the first exhaust port  52 , or the second exhaust port  48 . Therefore, the first wing  56 A and the second wing  56 B work together to maintain an open flow path between the inlet port  44  and the second outlet port  46 , and between the inlet port  44  and the actuator chamber  42 . In the open position, the spring  38  is compressed and the air spring chamber  32  contains fluid at high pressure. 
     In the open position, the spring  38  is fully compressed and the air spring chamber  32  contains pressurised fluid. Therefore, the net force acting on the spool  34  is such that the force due to spring  38  compression and fluid contained in the air spring chamber  32  acting on the spool  34  is larger than the force due to the fluid contained within the actuation chamber  42  acting on the spool  34 . The net force pushes the spool  34  to close the valve assembly  10 . Providing a combination of the spring  38  and the air spring to close the valve assembly  10  results in much faster switching times in comparison to any known devices of this type. 
     In relation to the blow moulding system  400  of  FIG. 7 , when the valve assembly  10  is in the open position, working fluid flows from the valve assembly  10  via the second outlet port  46  into the second control chamber  420  of the main valve  410 . At the same time, there is no working pressure in the first outlet port  50 , which is connected to the second control chamber  420 . The net force on the piston  416  is such that the flowpath between the inlet port  422  and the second outlet  424  is opened by the piston  416 . In this position, pressurised fluid is induced into the moulding apparatus  430  and blow moulding can take place. The preform  428  is moulded to the shape of the mould  426  in order to manufacture a container, for example a plastic bottle or similar. The main valve  410  will enable pressurised fluid to charge into the preform for as long as the main valve  410  is open, which in turn means that as long as the valve assembly  10  is in the open position, the preform  428  will remain pressurised. In order to provide appropriate conditions for manufacturing items out of preforms, the main valve  410  must be shut after a period of time. The valve assembly  10  controls the length of time during which the main valve  410  is open. 
     As regarding the second embodiment of the invention shown in  FIGS. 8 and 9 , maintaining the valve assembly  110  in the open position is achieved using similar means as those described above in relation to the first embodiment of the valve assembly  10 . The seal  154  abuts walls of relevant recesses  122 A and  122 B at the same locations and in a similar fashion to the first embodiment. The main difference being that the second embodiment has no air spring channel, so no vacuum or low pressure is maintained in such a channel. In order to return the spool  134  to the closed position, the pressure within the pilot chamber  142  acting on the spool  134  is counteracted by the spring force of the spring  138 . For the valve assembly  110  to shut correctly, the spring  138  must provide a much larger axial force than the actuator  17  connected to the pilot chamber  142 . This valve assembly  110  also achieve opening of the flowpath of the main valve  410 , thus enabling fluid to enter the blow moulding apparatus  430  so as to shape the preform  428 . 
     Regarding the third embodiment of the invention shown in  FIG. 10 , the seal  254  of the valve assembly  210  operates in a similar way to that described in relation to the first and second embodiment. The difference between the valve assembly  210  and the valve assembly  10  is that channels for delivering working fluid to the air spring or to and from the actuator are not present in the valve assembly  210 . Actuation is purely mechanical, achieved by means of the plunger  280 . In the open position, the plunger  280  applies an axial force onto the spool  234 , thus opening a flowpath between the inlet port  244  and the first outlet port  250 , with the first exhaust port  252 , the second outlet port  246  and the second exhaust port  248  not fluidly connected to a pressure supply. 
     Clauses 
     1. A valve ( 10 ) comprising a bore ( 14 ) extending about an actuation axis (A), an inlet port ( 44 ), a first outlet port ( 50 ), and a first exhaust port ( 52 ) wherein a spool ( 34 ) inside the bore ( 14 ) is actuated between a first working position and a second working position, and a first seal wing ( 56 A) arranged on the spool ( 34 ),
         wherein a diameter of the spool ( 34 ) is smaller than a diameter of the bore ( 14 ) thus establishing a first fluid path between the inlet port ( 44 ) and the first outlet port ( 50 ) and establishing a second fluid path between the first outlet port ( 50 ) and the first exhaust port ( 52 );   a first annular recess ( 22 A) radially extending from the bore ( 14 ) and being in permanent fluid connection with the first outlet port ( 50 ), the first recess ( 22 A) comprising an outer first recess wall ( 24   a ) next to the first exhaust port ( 52 ) and an inner first recess wall ( 24   b ) next to the inlet port ( 44 );       

     whereby the first seal wing ( 56 A) is arranged on the spool ( 34 ), such that:
         in the first working position, the first seal wing ( 56 A) abuts to the outer first recess wall ( 24   a ), thus closing the second flow path and opening the first flow path;   in the second working position, the first seal wing ( 56 A) abuts to the inner first recess wall ( 24   b ), thus closing the first flow path and opening the second flow path.       

     2. The valve ( 10 ) of the preceding claim further comprising a second outlet port ( 46 ), a second exhaust port ( 48 ), and a second seal wing ( 56 B),
         wherein a third flow path is established between the inlet port ( 44 ) and the second outlet port ( 46 ) and a fourth flow path is established between the second outlet port ( 46 ) and the second exhaust port ( 48 );   a second annular recess ( 22 B) radially extending from the bore ( 14 ) and being in permanent fluid communication with the second outlet port ( 46 ), the second annular recess ( 22 B) comprising an outer second recess wall ( 24   d ) next to the second exhaust port ( 48 ) and an inner second recess wall ( 24   c ) next to the inlet port ( 44 ).       

     whereby the second seal wing ( 56 B) is arranged on the spool ( 34 ), such that:
         in the first working position, the second seal wing ( 56 B) abuts to the second inner recess wall ( 24   c ), thus closing the fourth flow path and opening the third flow path;   in the second working position, the second seal wing ( 56 B) abuts to the outer second recess wall ( 24   d ), thus closing the third flow path and opening the fourth flow path.       

     3. The valve ( 10 ) of any preceding claim wherein the valve ( 10 ) includes a housing ( 12 ), a first pressure cap ( 18 ), and a second pressure cap ( 16 ), the housing ( 12 ) having the bore ( 14 ), and having a first housing end ( 12 A) and a second housing end ( 12 B), wherein the first pressure cap ( 18 ) is disposed at the first end ( 12 A) of the housing ( 12 ), and the second pressure cap ( 16 ) disposed at the second end ( 12 B) of the housing ( 12 ). 
     4. The valve ( 10 ) of claim  3  further comprising a biasing element ( 38 ) for returning the valve ( 10 ) from the second working position to the first working position and disposed around the spool ( 34 ) and between the spool ( 34 ) and the second pressure cap ( 16 ). 
     5. The valve ( 10 ) of any preceding claim wherein the first seal wing ( 56 A) is flexible, such that, in the first working position of the valve ( 10 ), it is adapted to abut the first outer recess wall ( 24   a ) so as to elastically deflect. 
     6. The valve ( 10 ) of any of the claims  2  to  4 , wherein the second seal wing ( 56 B) is flexible, such that, in the second working position of the valve ( 10 ), it is adapted to abut the second outer recess wall ( 24   d ) so as to elastically deflect. 
     7. The valve ( 10 ) of any of the claims  2  to  6  comprising a tubular connector ( 70 ) disposed around the spool ( 34 ) and extending axially between the first ( 56 A) and second ( 56 B) seal wing, wherein the first seal wing ( 56 A), the second seal wing ( 56 B), and the tubular connector ( 70 ) together form a unitary seal ( 54 ). 
     8. The valve ( 10 ) of any preceding claim further comprising a first dynamic seal ( 40 A) and a second dynamic seal ( 40 B), said first ( 40 A) and second ( 40 B) dynamic seal being circumferentially disposed around each end of the spool ( 34 ), the dynamic seals ( 40 A,  40 B) being configured to centre the spool ( 34 ) such that the spool ( 34 ) does not directly contact the bore ( 14 ) of the housing ( 12 ). 
     9. The valve ( 10 ) of claim  3 , wherein the second pressure cap ( 18 ) comprises a secondary bore ( 32 B) for receiving the spool ( 34 ), wherein the secondary bore ( 32 B) is permanently fluidly connected to the second annular recess ( 22 B), such that the secondary bore ( 32 B) is configured to act as an air spring for transmitting the spool ( 34 ) from the second working position to the first working position. 
     10. The valve ( 10 ) of claims  8  and  9 , wherein the first dynamic seal ( 40 A) is arranged between the bore ( 14 ) and the spool ( 34 ) and the second dynamic seal ( 40 B) is arranged between the spool ( 34 ) and the secondary bore ( 23 B). 
     11. The valve ( 10 ) of any preceding claim further comprising a first chamfered edge ( 26 A) disposed at an intersection between the bore ( 14 ) and the inner first recess wall ( 24   b ). 
     12. The valve ( 10 ) of any of the claims  2  to  4  and  6  to  10 , further comprising a second chamfered edge ( 26 B) disposed at an intersection between the bore ( 14 ) and the inner second recess wall ( 24   c ). 
     13. The valve ( 10 ) of any preceding claim, wherein the spool ( 34 ) includes a first radially extending protrusion ( 36 A) for accommodating the first seal wing ( 56 A). 
     14. The valve ( 10 ) of any of the claims  2  to  4 ,  6  to  10 , and  12 , wherein the spool includes a second radially extending protrusion ( 36 B) for accommodating the second seal wing ( 56 B). 
     15. The valve ( 10 ) of any preceding claim wherein the first seal wing ( 56 A) has a diameter which is smaller than a diameter of the first recess ( 22 A). 
     16. The valve ( 10 ) of any of the claims  2  to  4 ,  6  to  10 ,  12  and  14 , wherein the second seal wing ( 56 B) has a diameter which is smaller than a diameter of the second recess ( 22 B). 
     17. The valve ( 10 ) of claim  11 , wherein, in the second working position, the first sealing wing ( 56 A) is sheared between the first chamfered edge ( 26 A) of the first recess ( 22 A) and the first protrusion ( 36 A) so as to establish a fluid tight contact patch therebetween, while the second seal wing ( 56 A) bears against the outer second recess wall ( 24   d ), so as to deflect from the second protrusion ( 36 B), forming a gap therebetween. 
     18. The valve ( 10 ) of claim  12 , wherein, in the first working position, the second sealing wing ( 56 B) is sheared between the second chamfered edge ( 26 B) of the second recess ( 22 B) and the second protrusion ( 36 A) so as to establish a fluid tight contact patch therebetween, while the first seal wing ( 56 B) bears against the outer first recess wall ( 24   d ), so as to deflect from the first protrusion, forming a gap therebetween. 
     19. The valve ( 10 ) of any preceding claim further comprising an actuator operatively connected to the spool ( 34 ) for moving the spool ( 34 ) from the first working position to the second working position, where the actuator is: electromechanical, hydraulic, or pneumatic. 
     20. The valve ( 10 ) of claims  3  and  19 , wherein the actuator is disposed on or within the first pressure cap ( 18 ). 
     21. The valve ( 10 ) of any preceding claim, wherein the spool ( 34 ) comprises of a first module ( 34 A) and a second module ( 34 B), wherein the second module ( 34 B) receives the first module ( 34 A) thus forming an interference fit therebetween. 
     22. The valve ( 10 ) of claim  13  or  14 , and  21 , wherein the first module ( 34 A) includes the first radially extending protrusion ( 36 A), and wherein the second module ( 34 B) includes the second radially extending protrusion ( 36 B). 
     23. The valve ( 10 ) of claim  22 , wherein the biasing element ( 38 ) is clamped between the second protrusion ( 36 B) and the second pressure cap ( 16 ). 
     24. The valve ( 10 ) of any preceding claim, wherein the first exhaust port ( 52 ) is disposed on an inside surface of the bore ( 14 ) and is permanently fluidly connected to the second fluid port ( 46 ), or wherein the second exhaust port ( 48 ) is disposed on an inside surface of the bore ( 14 ) and is permanently fluidly connected to the first fluid port ( 50 ). 
     25. A blow moulding machine ( 400 ), comprising:
         a main valve ( 410 ) comprising a housing ( 412 ) and a piston ( 416 ) moveable within a bore ( 414 ) of the housing ( 412 ), the housing ( 412 ) having at least one inlet port ( 422 ) and at least one outlet port ( 424 ) in fluid communication with the inlet port ( 422 ), the housing ( 412 ) also comprising a first control port and a second control port, the first control port being in fluid communication with a first control chamber ( 418 ) and the second fluid port being in fluid communication with the second control chamber ( 420 ),   a valve ( 10 ) as defined in of any of the preceding claims, wherein the first outlet port ( 50 ) is in fluid communication with the first control chamber ( 418 ), and the second outlet port ( 46 ) is in fluid communication with the second control chamber ( 420 ), such that when the valve ( 10 ) is in the open position, the piston ( 416 ) opens a flow path between the inlet port ( 422 ) and the outlet port ( 424 ), and when the valve ( 10 ) is in the closed position, the piston ( 416 ) closes the flow path between the inlet port ( 422 ) and the outlet port ( 424 ).       

     26. The blow moulding machine of any preceding claim, wherein the main valve is pressure balanced. 
     27. The blow moulding machine of any preceding claim, wherein the blow moulding valve is for manufacturing plastic containers or plastic bottles. 
     28. A seal ( 54 ), comprising:
         a tubular section ( 70 ) extending along an axis (A) and having a first and a second end;   a first wing section ( 56 A) disposed at the first end of the tubular section ( 70 ), the first wing section ( 56 B) extending radially away from the first end of the tubular section ( 70 );   a second wing section ( 56 B) disposed at the second end of the tubular section ( 70 ), the second wing section ( 56 B) extending radially away from the second end of the tubular section ( 70 );       

     wherein the first wing section ( 56 A) and the second wing section ( 56 B) extend axially along the axis away from one another, 
     wherein the tubular section ( 70 ), the first wing section ( 56 A), and the second wing section ( 56 B) together define a unitary seal for a spool valve. 
     29. A method of assembling a valve of any preceding claim, comprising the steps of:
         providing: a housing ( 12 ) having a bore ( 14 ) extending along an axis (A), and having a first end ( 12 A) and a second end ( 12 B); a modular piston ( 34 ) having a first module ( 34 A) and a second module ( 34 B), wherein the first module ( 34 A) is received in an opening of the second module ( 34 B), the first module ( 34 A) having a first radial protrusion ( 36 A) and the second module ( 34 B) having a second protrusion ( 36 B); a unitary seal ( 54 ) having a tubular ( 70 ) section with a first and a second end; a biasing spring ( 38 ); and a cap ( 16 )   providing a tubular insert ( 60 ) for introducing the unitary seal ( 54 ) into the bore ( 14 ) of the housing ( 12 ), the tubular insert ( 60 ) having a bore section ( 64 ) for engaging the bore ( 12 ) and an exterior section ( 62 ) for compressing the seal ( 54 );   inserting the first module of the piston into the housing;   forcing the unitary seal ( 54 ) through the exterior section ( 62 ) so as to compress the seal ( 54 ) and so as to insert the compressed seal ( 54 ) into the bore section ( 64 );   removing the tubular insert ( 60 ) from the bore ( 14 ) to allow the seal ( 54 ) to expand into the recesses of the housing ( 12 ) and to mount the unitary seal ( 54 ) on the first module ( 34 A) of the piston ( 34 ) so that the seal ( 54 ) is in contact with the first radial protrusion ( 36 A);   assembling the second module ( 34 B) onto the first module ( 34 A) so that the seal ( 54 ) is also in contact with the second radial protrusion ( 36 B);   disposing the biasing spring ( 38 ) on the second radial protrusion ( 36 B);   attaching the cap ( 16 ) to the second housing end ( 12 B), such that the spring ( 38 ) is clamped between the second protrusion ( 36 B) and the cap ( 16 ).