Abstract:
A valve in a pipeline is automatically configured to close the flow through the pipeline in the event of a pipeline rupture or similar event. During normal flow, a valve element is maintained in an open position. However, in the event of a rupture, the resulting pressure drop across the valve is sensed and causes the valve element to move to a closed position.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Field of the Invention 
         [0002]    This invention is directed to an automatic shutoff valve for a fluid pipeline, which may convey gas or oil for example. The valve is located within the pipeline and will automatically close in response to a drop in pressure which may be the result of a pipeline rupture or other emergency shutdown event. 
         [0003]    Description of Prior Art 
         [0004]    Pipeline owners are required by federal regulations to provide the capability of emergency shutdown of pipeline. Typically this is accomplished by providing valves in the pipeline which are either manually controlled, remotely controlled, or operate automatically. 
         [0005]    Experience has indicated that excessive delays have occurred in manually closing valves after a rupture and that without early detection, remotely controlled valves are of little value. Industry studies have determined that:
       1. Both field and computer simulation studies have shown the major reliability problem of these systems results from the fact that no pipeline flow parameter has been identified that will serve as an adequate line break detection signal in all applications.   2. Rate of pressure drop (ROPD), for example, is inadequate in many pipeline applications where operating transients from compressor stations, valve change, etc. are comparable in magnitude to the transient signals developed by a line break. Other approaches have been attempted, but none have demonstrated adequacy for all applications.   3. The safety benefits of early valve closure lies in shortening the duration of line blowdown and when early ignition occurs, of reducing the effect of long-term thermal radiation.   4. In most cases, ignition occurs within the first 10 minutes. Early shutoff will reduce the prolonged heating of nearby structures and reduce the magnitude of injuries and property damage.       
 
         [0010]    An ideal shutoff valve will close in seconds, not minutes or hours. An ideal automatic shutoff valve will not rely upon external instrumentations and human interpretation to determine when to close the valve and does not require an external source of power to close the valve. Also the ideal valve does not require a remote action to close the valve and does not exhibit a fail-safe function to needlessly close. Lastly an ideal valve would be less expensive than automatic and remote control valves and would be based on current and proven technology to the extent possible. 
       BRIEF SUMMARY OF THE INVENTION 
       [0011]    These and other needs in the art are addressed by the instant invention by providing an automatic shutoff valve that is actuated by sensing a drop in pressure in the flow line. A valve closure member is responsive to a higher flow rate and pressure drop across the valve to move a valve element to a closed position. The valve element is normally held in an open position by a static force provided for example by weights attached to the valve element or by the weight of the valve element itself. The valve element may be a hinged flapper type valve element or a gate type valve element. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    For a detailed description of the preferred embodiments of the invention, reference will now be made to the accompanying drawings in which: 
           [0013]      FIG. 1  is a cross sectional view of a first embodiment of the invention. 
           [0014]      FIG. 2  is a cross sectional view of a second embodiment of the invention. 
           [0015]      FIG. 3  is a cross sectional view of a third embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0016]    To illustrate various illustrative embodiments of the present invention, the following examples are provided. 
         [0017]    As shown in  FIG. 1 , a first embodiment of the invention includes a valve housing having an inlet portion  72  with an inlet flow path  1 , a middle portion  3  and an outlet portion  73  having an outlet flow path  2 . Inlet portion  1  and outlet portion  2  are adapted to be suitably connected in a pipeline by welding or bolts as in known in the art. 
         [0018]    A flapper valve element  4  is pivotally connected at  6  to an internal portion of the middle housing portion  3  and is normally held in an open position as shown in  FIG. 1 . A valve seat  5  cooperates with flapper valve element  4  to shutoff flow through the valve as shown in phantom at  27 . 
         [0019]    The valve housing further includes a vertically extending portion  71  which may be cylindrical or rectangular in shape. Vertical extending housing  71  is closed at its upper end by a top plate  19  which includes an opening  20  for the valve stem  7 . 
         [0020]    A fluid cylinder  15  is attached to the top plate  19  and in turn is closed by a second top plate  18  which includes an opening  75  for the valve stem  7 . 
         [0021]    Flapper valve element  4  is normally held in an open position by a weight  9  suspended around a pulley  10  or other mechanism within housing  71 . A cable  11  is attached at one end to weight  9  and at a second end to flapper valve element  4  at  12 . 
         [0022]    A valve stem  7  extends through top plates  18  and  19  through openings  75  and  20  and is connected to flapper valve element  4  by a flexible link  76  that is pivoted at  8  to both flapper valve element  4  and valve stem  7  to allow the flapper valve element to move from the open position to the closed position  27  shown in phantom in  FIG. 1 . 
         [0023]    A piston  73  is positioned within fluid cylinder  15  and is fixedly attached to valve stem  7 . The volume  49  above piston  73  is in fluid communication with the inlet flow path  1  via port  78 , control lines  21 ,  49 ,  17  and valve  76 . Valve  22  allows external pressure to reposition the piston and flapper valve element  4 . A vent  23  allows for purging or relieving pressure acting in control line  17 . 
         [0024]    The lower volume  48  of cylinder  15  is in fluid communication with outlet  2  of the valve via control line  16 ,  26 , and port  79 . A valve  25  allows for external pressure to reposition the piston  13  and valve stem  7 . A vent  24  allows for purging or relieving pressure within control line  16 . 
         [0025]    Upper portion  49  of the fluid cylinder  15  contains pressure equal to the inlet pressure of the valve at  1  and the lower portion  48  of the fluid cylinder  15  contains pressure equal to the outlet pressure of the valve at  2 . In a steady state open flow situation, the pressure drops across the valve is not sufficient to overcome the force of the weight  9 . However, should a rupture occur, the pressure drop across the valve will be significantly higher. When a pipeline rupture occurs, the differential pressure across the valve increases with the square of the gas flow rate and velocity. Depending on the proximity to the rupture, the differential pressure across the valve can increase by a factor of five to twenty five or even more depending on how close the valve is to the rupture. 
         [0026]    Thus when a rupture occurs, the pressure acting on the top of piston  13  is great enough to overcome the force of the weight  9 . This causes valve stem to move downwardly to move flapper valve element to a closed position shown in phantom in  FIG. 1 . 
         [0027]    A second embodiment of the invention is shown in  FIG. 2 . The operating principles are very similar to the embodiment of  FIG. 1 . A gate valve element  34  having an opening  90  however is utilized in lieu of a flapper valve element. 
         [0028]    Referring to  FIG. 2 , the valve includes a central valve housing  62  having an inlet flow path  31  and an outlet flow part  32 . An inlet connector  61  includes a port  83  and outlet connector  63  includes a port  84 . Inlet and outlet connectors  61  and  63  are suitably connected for example by welding or bolts to central valve housing  62 . A lower valve housing  33  which may be circular in shape extends below central valve housing  62  and houses a retainer member  35  which supports gate valve element  34  in the closed position shown in phantom at  89 . A pair of seals  36  are located on the sides of the gate valve to seal the valve in the closed position. 
         [0029]    The valve housing further includes an upper portion  81  which houses one or more weights  38  which are attached to the gate valve element  34  at  40  via a pair of cables  41  that pass over a pair of pulleys  39  or other mechanisms secured within upper housing member  81 . Thus weights  38  exert an upward force on valve stem  37  and gate valve  34  to keep the valve open during normal operation. 
         [0030]    Top plate  42  closes upper housing portion  81  and has an opening  43  through which valve stem  37  passes. A fluid cylinder  44  is positioned on top of top plate  42  and includes a second top plate  47  which has an opening  82  through which valve stem  37  passes. A seal  86  surrounds valve stem  37  at the opening  82 . A passageway  87  extends through second top plate  47  and is connected to control line  52 . 
         [0031]    A piston  45  is fixedly secured to valve stem  37  and is located within fluid chamber  44 . 
         [0032]    Pressure at valve inlet  31  is communicated to the upper side of piston  45  via port  83  and control line  39 ,  64 , and  52 . Valve  50  allows external pressure to be used to test or reposition the valve to a closed position. A vent  51  allows venting of pressure within control lines  39 ,  64 ,  52 . 
         [0033]    Pressure at valve outlet  32  is communicated to the lower side of piston  45  via port  84 , control lines  53 ,  65 , and  56 . 
         [0034]    Valve  54  allows venting and permits an external pressure source to be used to test or reposition the valve to an open position. Valve  55  is a vent valve to allow venting of the pressure within control lines  56 ,  65 , and  53 . 
         [0035]    In the normal flow condition the magnitude of the weights  38  are selected to maintain gate valve  34  in the open position shown in  FIG. 2 . The differential pressure acting on the piston during normal operation is not sufficient to overcome the force of the weights and gate valve  34 . 
         [0036]    However, as explained above with references to the embodiment of  FIG. 1 , a rupture in the pipe line will cause a significant pressure drops across the valve that will be sufficient to overcome the force of the weights and thus move piston  45  in a downwardly direction. This in turn will cause gate valve to move downwardly and close the gate valve as shown in phantom at  89  thereby shutting off flow through the valve in a manner known in the art. 
         [0037]      FIG. 3  illustrates a third embodiment of the invention. The embodiment utilizes the weight of the valve stem and gate valve as the biasing force to maintain the valve in a closed position. An increase in the differential pressure across the valve results in an upward movement of the piston, valve stem, and gate valve assembly. 
         [0038]    The valve housing  103  includes an inlet  101  and outlet  102 . The valve can be secured to pipeline sections  99  and  104  as is known in the art. The valve housing also includes a lower portion  107  which includes a guide  105  to position the gate valve  106  in the open position. 
         [0039]    The valve housing further includes an upper portion  108  having a top plate  109  which includes an opening  125 . A fluid chamber  110  is positioned on top plate  109  and is closed by a second top plate  115  which has an opening  124  and seal  122  through which valve stem  112  extends. A fluid passageway  123  also extends through top plate  123 . 
         [0040]    A piston  111  is positioned within fluid chamber  110  and is fixed to valve stem  112 . Valve stem  112  is attached to gate valve  106  which has an opening  129  which allows for fluid flow through the valve in an open position as is known in the art. 
         [0041]    Inlet fluid pressure is applied to the bottom  114  of fluid chamber  110  via port  116 , conduit  118  and inlet port  130 . A valve  121  allows for venting of fluid pressure within conduit  118 . 
         [0042]    Outlet fluid pressure is applied to the top portion  113  of fluid cylinder  110  via port  117 , conduits  120 ,  119  and passageway  123  in top plate  115 . A vent valve  126  allows venting and connection to an external pressure source to be used to test or reposition the valve. 
         [0043]    In this embodiment, the combined weight of valve stem  112 , piston  111 , and gate valve  106  is sufficient to maintain the valve in an open position as shown in  FIG. 3 . However should a rupture occur, the pressure differential across the valve will increase, thus causing piston  111  to move upwardly. This will in turn cause gate valve  106  to move upwardly to a closed position. 
         [0044]    The inlet and outlet pressure ports could also be located in the pipeline adjacent to the inlet and outlet of the valve, or further upstream of the inlet and further downstream of the outlet to increase the pressure drop across the control ports. 
         [0045]    Grooves or serrations  88  or other types of surface roughness as shown in  FIG. 2  in flow path  91  may be machined or otherwise provided to the inside surface of the central valve housings in all the embodiment to increase the pressure drop across the valve. Additionally valves may be provided in control lines  21 ,  26 ,  39 ,  53 ; and  118 ,  120 . Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations may be made herein without departing from the spirit and scope of the invention as defined by the appended claims.