Abstract:
A sealing mechanism for a gas chromatograph machine includes a weldment attachment mountable at the weldment assembly of the machine. The attachment has a passage therethrough for gas communicated to the weldment assembly. An actuator imparts a direct force on the weldment attachment to move it linearly towards an injection port of the machine and to sealingly clamp the weldment attachment onto the port. Torsional forces are not applied on the weldment attachment by the actuator.

Description:
[0001]     This invention relates to a mechanism used for sealing two sealing halves in a gas chromatograph machine and specifically for sealing the injection port of a gas chromatograph machine.  
       BACKGROUND OF THE INVENTION  
       [0002]     Gas chromatography is a technique used for the separation of mixtures. In gas chromatography, the sample is often introduced as a liquid into the injection port whereafter it is volatilized. An inert gas is used as a carrier to propel the volatilized sample into the gas chromatographic column where the sample mixture is separated into its components. Each separated component is further propelled by the carrier gas through the exit of the gas chromatographic column into a detector. The detector then provides information regarding the amount and identity of each component of the sample mixture.  
         [0003]     The injection port is the point at which the sample is introduced into the machine prior to separation of components. The injection port typically operates at elevated temperatures to ensure that the sample mixture is vaporized and transitions into the gas phase prior to separation entry to the chromatographic column. To assist this vaporization a disposable liner made of an inert material such as glass or quartz is placed within the injection port. A side effect of this process is that the liner also traps non-volatile components within the sample mixture. After repeated exposure to sample introductions, the injection port liner may loose its inert characteristics or become dirty and thus require replacement.  
         [0004]     When using dirty sample matrices liner replacement is required frequently. This requires the uncoupling of two sealing surfaces to remove and replace the liner, followed by a recoupling of these sealing surfaces. This sealing is usually provided through the compression of an o-ring or ferrule around the outer diameter of the liner and positioned between the two sealing halves of the injection port body.  
         [0005]     The normal way of forming this compression is through the use of a threaded weldment nut assembly onto an injection port body which contains a sealing bevel and metal tube to house the injection port liner. Such an arrangement is illustrated in  FIG. 1 . Components of the threaded nut assembly usually include gas introduction lines connected to a sealing septum to bring the carrier gas to the inlet. Once the weldment assembly is removed a liner and seal is placed into the injection port body. The threaded weldment nut is then turned onto matching threads on the injection port body producing a compression seal on an O-ring around the outer diameter of the injection port liner. This compression seal couples the liner and allows the flow of carrier gas supply through the liner into the gas chromatographic column.  
         [0006]     The threaded weldment nut assembly often requires tools such as a wrench to rotate the nut onto the thread of the injection port body. The weldment nut is inductively heated when it is in contact with the injection port body, resulting in it often being too hot to handle (temperatures up to 350° C.). When removing the weldment nut from the injection port body it must be turned several times, often with a wrench, before it is released from the injection port body. After replacing the old liner, the threaded weldment nut is cool and thus exhibits difficulty in rethreading onto the thread of the hot injection port body. This can result in cross threading and seal leakage. Liner seals may also be damaged and leak due to torsional forces produced by rotating the weldment nut.  
         [0007]     Additionally, this process of replacing the liner may be dangerous for operators if their hands contact the hot components of the injection port body which can easily occur when rotating the weldment nut assembly. The process of unthreading and rethreading may take several minutes to accomplish which can have deleterious effects on the system by exposing the gas chromatograph and column to air.  
         [0008]     The present invention seeks to improve the ease and efficiency of removing and replacing the weldment assembly and on the whole making it safer for operators to use.  
       SUMMARY OF THE INVENTION  
       [0009]     In one embodiment the invention is a sealing mechanism for a gas chromatograph machine comprising: 
        a weldment attachment mountable at the weldment assembly of a gas chromatograph machine and having a passage therethrough for gas communicated to the weldment assembly; and 
 
 actuating means for actuating a direct force on the weldment attachment to linearly move it towards an injection port of the gas chromatograph machine and sealingly clamp the weldment attachment onto the injection port, wherein the actuating means does not apply torsional forces on the weldment attachment. 
       
 
         [0012]     In another embodiment the invention is sealing mechanism for a gas chromatograph machine comprising: 
        an annular base mountable at the weldment assembly of a gas chromatograph machine, the base having a passage therethrough for gas communicated to the weldment assembly;     a lever pivotally connected to the annular base and pivotally attached to an injection port of the gas chromatograph machine, wherein the base is adapted to be seated on top of the injection port and sealed against thereto by pivotally moving the lever to apply a direct force and clamp the base onto the injection port.        
 
         [0015]     In still another embodiment the invention is a sealing mechanism for a gas chromatograph machine comprising: 
        an annular base mountable on the inlet weldment assembly of a gas chromatograph machine, the base providing a passage therethrough for gas;     a latch having two arms pivotally connected on opposing sides on the exterior circumference of the annular base, the arms being provided with hinging means to hingedly attach the latch to a corresponding attachment on an injection port of the machine, the base being mountable on the injection port, wherein the latch is pivotally levered against the injection port to directly clamp the base onto the injection port in sealing engagement and without imparting torsional force on the base.        
 
         [0018]     In yet another embodiment the invention is a method of sealing a weldment assembly and an injection port on a gas chromatograph machine including: 
        mounting a weldment assembly onto the injection port, wherein the weldment assembly includes a latch having two arms and is pivotally connected to opposite sides of the exterior circumference of an annular base, the arms having coupling means for coupling with complementary means located at the injection port in order to mount the latch onto the injection port; and     pivotally levering the latch at the coupling to clamp the base down onto the injection port.        
 
         [0021]     In still another embodiment the invention is a method of sealing a weldment assembly and an injection port on a gas chromatograph machine including: 
        mounting a weldment attachment at the weldment assembly, the weldment attachment providing a passage therethrough for gas communicated to the weldment assembly;     actuating an actuating means connected to the weldment attachment, and thereby applying a direct force on the weldment attachment moving it towards the injection port and sealingly clamping the weldment attachment against the injection port, wherein torsional forces are not applied on the weldment attachment by the actuating means.       
 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]     The present invention is described further by way of example with reference to the accompanying drawings of which:  
         [0025]      FIG. 1  is a schematic side view of an injection port of a gas chromatograph machine sealed using a known assembly;  
         [0026]      FIG. 2  is a side schematic view of an injection port of a gas chromatograph machine prior to sealed using a sealing mechanism according to one embodiment of the present invention;  
         [0027]      FIG. 3  is a view similar to  FIG. 2  but showing the mechanism mounted on the injection port in an unlocked position;  
         [0028]      FIG. 4  is a view similar to  FIG. 3  but showing the mechanism in the locked position;  
         [0029]      FIG. 5  is an exploded perspective view of one embodiment of the sealing mechanism;  
         [0030]      FIG. 6  is a plan view of a latch used in the first embodiment of the sealing mechanism;  
         [0031]      FIG. 7  is a perspective view of the latch of  FIG. 6 ;  
         [0032]      FIG. 8  is a perspective view of a base ring used in the first embodiment of the sealing mechanism;  
         [0033]      FIG. 9  is a side sectional view of the base ring of  FIG. 8 ;  
         [0034]      FIG. 10  is a perspective view of an adapter ring used in the first embodiment of the sealing mechanism;  
         [0035]      FIG. 11  is a side view of the adapter ring of  FIG. 10 ;  
         [0036]      FIG. 12  is a side view of a sealing mechanism in the locked position; and  
         [0037]      FIG. 13  is the same view as  FIG. 12  but showing the sealing mechanism in the locked position. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0038]      FIG. 1  illustrates a known device for sealing an injection port body of a gas chromatograph machine. A weldment frame  11  including a sealing septum  18  and septum nut  19  carries an internally threaded weldment nut A that is screwed onto a corresponding thread  17  on the injection port body  12 . Gas lines  13  connected to the weldment frame  11  are for communicating carrier gas to the weldment frame  11  the on to the injection port inlet  15  when sealed.  
         [0039]     In the following a preferred embodiment of a sealing mechanism of a gas chromatograph machine is described in detail. Essentially, sealing mechanism avoids the use of a thread to screw the weldment frame  11  onto an O-ring  14  of the injection port body  12 . Instead the mechanism uses a clamping force to form a tight and even seal between the injection port body and weldment frame. Accordingly, the present sealing mechanism eliminates any torsional forces involved in sealing the injection port and instead applies a direct force normal to the mouth of the injection port inlet  15  to create a direct and balanced seal. With this mechanism there is little chance of misalignment and damage or leakage caused by incorrect sealing.  
         [0040]     The preferred embodiment of the sealing mechanism employs a lever system to achieve a direct clamping force. However, it is understood that other mechanisms are also able to provide the necessary direct force to seal the injection port of a gas chromatograph and these are also described briefly below as alternate embodiments of the invention.  
         [0041]      FIG. 2  illustrates a sealing mechanism  10  spaced above injection port body  12  before mounting. The sealing mechanism employs a lever style configuration to apply a direct downward force to clamp weldment frame  11  to injection port body  12 . The sealing mechanism  10  incorporates weldment frame  11  and the gas lines  13  connected thereto to form a weldment assembly capable of being sealingly mounted onto the injection port body by way of a clamping force.  
         [0042]     In this embodiment, the sealing mechanism  10  includes a base ring  30  adapted to fit onto the underside of weldment frame  11  such that the gas lines communicate carrier gas through the weldment frame  11  and through a central flow aperture  36  of base ring  30 , which in turn is designed to be sealingly connected to inlet port  15  in the injection port body.  
         [0043]     Latch  20  is hinged to opposing sides of base ring  30  and in use is levered down to provide the clamping force for sealing.  
         [0044]      FIG. 2  schematically illustrates latch  20  pivoted to opposite sides of base ring  30 . To seal the injection port body the whole weldment assembly  10  is brought down and centered on the inlet port  15  as illustrated in  FIG. 3 . Base ring  30  is mounted over O-ring  14  to prepare for sealing. Latch  20  is then levered down to the position illustrated in  FIG. 4  thereby bringing base ring  30  and O-ring  14  close in contact to seal the injection port body.  
         [0045]     To retrofit the present sealing mechanism  10  to existing gas chromatograph systems some form of an adapter is required as an engagement means for latch  20 . In the present embodiment latch  20  is unable to properly engage with thread  17 . Accordingly, adapter ring  40  is fitted onto the existing external thread  17  and the latch engages this adapter. The adapter enables existing gas chromatograph machines to operate with the present sealing mechanism. Specifically, the adapter is screwed onto the existing thread  17  and sits on a seat surrounding inlet port  15 .  
         [0046]     FIGS.  2  to  4  schematically illustrate the adapter ring which has an internal thread that cooperates with external thread  17  and an exterior circumference onto which latch  20  can be anchored and levered down.  
         [0047]      FIG. 5  illustrates in an exploded format the various components defining the preferred sealing mechanism  10 , namely latch  20 , base ring  30  with lugs  31 , and adapter ring  40 .  
         [0048]     Latch  20  is illustrated in  FIGS. 6 and 7  and is substantially U-shaped and has a central portion  22  from which two side arms  21  extend in opposite directions bending through approximately 90° to terminate in broad flanges  23 , which face each other. Flanges  23  have a cambered profile and are each provided with a small aperture  24  designed to receive lugs  31  extending from opposite side edges  32  of base ring  30 .  
         [0049]     This connection provides a hinged pivoting relationship between latch  20  and base ring  30 .  
         [0050]     Central portion  22  of latch  20  is provided with an upstanding lever handle  25  which is used by an operator to, in use, take a hold of the latch to pull down and seal the injection port.  
         [0051]     Base ring  30  as illustrated in  FIGS. 8 and 9  is annular in shape and can be round, hexagonal or similar. Base ring  30  is substantially defined by a large ring  33  and an adjacent concentric small ring  34 . Flow aperture  36  is located along the axial center of the base ring. Small ring  34  acts as a spacer and complementarily communicates with the port  15  of injection port body  12 . The annular bottom edge  35  of small ring  34  contacts against the O-ring  14  located around the inlet port  15  on the injection port body  12  to form a seal. The underside of large ring  33  adjacent small ring  34  defines one of the clamping surfaces used in sealing the weldment frame to the injection port body.  
         [0052]     The other clamping surface to which the large ring  33  clamps is an upper annular edge  41  of the adapter ring  40 . Adapter ring  40  is illustrated in  FIGS. 10 and 11  and is an annular ring having an internal thread for cooperating with existing thread  17 , and a series of pins  44  provided on the exterior circumference extending radially outward. Once adapter ring  40  is screwed onto thread  17  at injection port inlet  15 , grub screws  42  radially located on opposite sides of body  43  of adapter ring  40  adjust and secure the position of adapter ring  40  with respect to the annular upstanding lip  16  of the injection inlet port  15 . The grub screws when tightened protrude through the inner circumference of adapter ring  40  and into the centre  45  of the ring. The screws are tightened by way of a hex-wrench which end locates in a corresponding grub screw aperture located on the exterior circumference of ring  40 . As the grub screws are tightened they extend through to the inner circumference of adapter ring  40  and engage with external thread  17 .  
         [0053]     On the exterior circumference of adapter ring  40  each pin  44  has a paired pin on a directly opposite point of the exterior circumference. In other words the paired pins are spaced 180° on the exterior circumference. Latch  20  is designed to hook onto one of the pair of pins  44  on the adapter ring  40 . The pair of pins  44  acts as the fulcrum or pivoting point for the latch  20  so that the latch can be levered down to seal the weldment assembly onto the injection port body  12 .  
         [0054]     As illustrated in  FIGS. 6 and 7 , each flange  23  on side arms  21  has a shaped recess  26  on an interior face of the flange such that the shaped recesses  26  on the two flanges face one another. The shaped recesses  26  are each adapted to receive one pin  44  in a pair. The shape of the recesses  26  is bent at an angle so that pins extending into the recesses are made to follow the shape from one end of the recess to the other.  
         [0055]     In use where the latch and base ring arrangement are mounted over the adapter ring with opposing pins  44  extending into the recesses  26 , pivoting movement of latch  20  moves the hinged joint at lugs  31  and consequently base ring  30 , directly over injection port  15  and down onto the port in a manner that clamps the base ring on top of the adapter ring. In the unsealed position latch  20  is substantially upright over the injection port body. This position can be seen in  FIG. 12 . From here the latch, base ring and rest of the weldment assembly, is mounted on the inlet port and the latch levered down to a substantially horizontal position to scoop around and clamp the base ring and hence weldment assembly, onto the adapter ring and injection port body.  
         [0056]     The sealing mechanism is illustrated in  FIG. 13  in the sealed position (the injection port body and part of the weldment assembly are not shown). The hinged joint at lugs  31  between latch  20  and base  30  is located sufficiently close to the shaped recess such that as the latch is pulled down, the hinged joint moves in a path around the recess terminating at a point lower than where it began.  
         [0057]     The cambered profile of the flanges  23  assist in smooth rotation of the latch arm by providing a cam surface acting as a support against an upper surface of the injection port.  
         [0058]     Accordingly, a tight seal is produced between the injection port body and weldment assembly. As there is no need for any turning movement on threads, the seal is formed with an even distribution of pressure around the base ring and adapter ring and is devoid of any misalignment or uneven forces that may be produced by the torsional forces involved in screwing a component on a thread. The compression created on the sealing O-ring is direct. Furthermore, the only tool required is a small hex-wrench; there is no need for the snap ring pliers and other tools required for assembling and disassembling known seals. The assembling and disassembling process is faster than that for known systems and the danger of injury to the operator is greatly reduced as direct contact with the hot injection port body is minimised.  
         [0059]     In threading the adapter ring on the injection inlet port the alignment of pins against the latch arms may not initially be correct. In this case the adapter ring can be rotated slightly to one side or the other until the latching arms align properly on the pins and the lever moves smoothly and firmly to clamp down the weldment assembly.  
         [0060]     The above embodiment describes a sealing mechanism used on existing gas chromatograph machines. Other embodiments are also possible. For example, where there is a possibility of providing this sealing mechanism on new machines, there would be no need for an external thread  17 . Lip  16  of the inlet port could be designed to cooperate directly with the latch without the need for an adapter ring.  
         [0061]     Alternatively external thread  17  may remain and instead the configuration of latch arms  21  could be changed in design to directly engage with external thread  17  while still allowing the latch to apply a downward clamping force. More specifically, the recesses inside arms  21  could be designed to fit onto, and lever from, part of the external thread  17  at the inlet  15  of the injection port body.  
         [0062]     In another embodiment of the sealing mechanism a device could be provided having a multi-pivoting hinge attached to one side of the injection port body. The hinge would be moveable in two or three dimensional planes. The device on a second side would be provided with a lock down clip or lever so that the device could be used to apply non-torsional pressure to the sealing surface and locked once sealed.  
         [0063]     A simplified version of the sealing mechanism would not use shaped recesses for pivoting but a simple hinge that would still allow the latch to be pulled down and lifted up without any torsional force.  
         [0064]     In still an alternate embodiment the necessary direct pressure required to seal the two surfaces could be applied using pneumatic or hydraulic means. This may, for example, involve pneumatic pressure from an external compressed supply used in connection with the weldment assembly to sealingly force it onto the O-ring. The actuator could, for example, be a pneumatic ram mounted on a frame supported by the injection port body. A lock means would ensure that the sealing engagement is retained.  
         [0065]     A two way valve in the pneumatic line would dictate in which direction the pneumatic force is to be provided, namely whether to seal or unseal the injection port. Hydraulic means would operate in a similar manner.  
         [0066]     In a further embodiment the non-torsional direct force could be applied using magnetic attraction. Traditional magnets or electromagnetic devices could be used to form an attraction between the weldment assembly and the inlet port to firmly seal the two together. In the case of electromagnetic instruments, magnetic attraction may be used locate and create the initial seal and a regular locking device used to maintain the seal.