Abstract:
A pressure surge sensor has a body having a cylinder passage, a magnetically actuated electrical switch mounted on the body, and a piston member movable along the passage relative to the switch. The piston member carries a magnet. When the cylinder passage is coupled to a fluid pressure surge source, a fluid pressure surge applied causes the piston member to move along the cylinder passage relative to said switch, thereby actuating the switch. A breakable retainer element restrains the piston member against movement, and the piston is freely movable along the cylinder passage, after release by the retainer. The pressure surge sensor is suitable to be arranged downstream of a rupture disc, which releases overpressure of a pressurised apparatus, for example an extrusion apparatus, or a gas handling or gas storage system.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to a pressure surge sensor, which is particularly suitable for use with a pressure relief rupture disc. The invention also relates to an assembly comprising a pressure surge sensor and a pressure relief rupture disc. 
       BACKGROUND TO THE INVENTION AND PRIOR ART 
       [0002]    Rupture discs, also commonly known as bursting discs, are well known safety pressure relief devices, which are designed to rupture reliably at a predetermined pressure differential (rupture/burst strength). 
         [0003]    It is well known in the many industries to provide such rupture discs for protecting pressure systems from over-pressurisation. One such rupture disc is for example disclosed in WO 03/031853. When the pressure at one side of the disc rises above a predetermined rupture strength, the disc ruptures thereby releasing pressure from the system. Typical applications are on reaction vessels and chambers, in the chemical, pharmaceutical and food industries. 
         [0004]    Another application is to provide a warning detection system in an extrusion apparatus or gas handling or gas storage system, to give a warning of over-pressure. 
         [0005]    It is also known in the art to provide a rupture disc with a rupture detector. WO 2005/054731 discloses a rupture disc type over-pressure detector having a rupture disc clamped at its flange between inlet and outlet pipe members. At the vent side of the device is mounted a magnet, its movement being sensed by a non-invasive sensor. When the pressure at one side of the disc rises above a predetermined rupture strength, the disc ruptures, thereby releasing pressure from the system and moving the magnet relative to the sensor. A signal is produced by the sensor, signalling that the rupture disc has ruptured. 
       SUMMARY OF THE INVENTION 
       [0006]    An object of the present invention is to provide an improved pressure surge detector, particularly a detector for use in combination with a rupture disc. A pressure surge detector, which provides an output signal when subjected to a pressure surge, must act reliably and quickly, when provided at the outlet side of a rupture disc. Particularly when the amount of pressurised gas released through the rupture disc, on rupture of the disc, is small, the sensor may be required to operate at relatively low pressure, for example 0.3 bar. 
         [0007]    According to this invention there is provided a pressure surge sensor comprising 
         [0008]    a body having a cylindrical passage, 
         [0009]    a magnetically actuated electrical switch mounted on said body, and 
         [0010]    a piston member movable along said passage relative to said switch, the piston member comprising a magnet, 
         [0011]    said cylinder being adapted to be coupled to a fluid pressure surge source, 
         [0012]    whereby a fluid pressure surge applied to said cylinder causes said piston member to move along said cylinder relative to said switch, thereby actuating said switch. 
         [0013]    By the invention a device which is simple in construction and reliable in operation, even at low pressure, may be provided. 
         [0014]    Preferably the sensor has a retainer restraining said piston member against movement along the cylinder from a first position in the cylinder relative to said switch, said retainer being adapted to release the piston member on application of a predetermined load to the piston member. The retainer may be a breakable element, adapted to be broken to release the piston member when said predetermined load is applied. 
         [0015]    Preferably the piston is freely movable along the cylinder, after release by the retainer, no mechanical element applying a driving force opposing its movement. 
         [0016]    The fluid pressure surge source is preferably a gas pressure surge source. 
         [0017]    Preferably the body has one or more vent holes connecting said cylinder to the exterior, said vent hole or holes being located so as to be opened by the movement of the piston along the cylinder to allow release of gas pressure from the side of the piston to which the pressure surge is applied. 
         [0018]    In a second aspect, the invention provides an assembly comprising a pressure surge sensor of the invention as described above and a rupture disc, the rupture disc being adapted to rupture at a predetermined rupture strength and arranged on rupturing to release a pressure surge to the pressure surge sensor. 
         [0019]    The invention also provides a pressurised apparatus, such as an extrusion apparatus or gas handling or gas storage apparatus, having such an assembly. 
     
    
     
       INTRODUCTION OF THE DRAWINGS 
         [0020]    Non-limitative embodiments of the invention will now be described by way of example with reference to the accompanying drawings. In the drawings: 
           [0021]      FIG. 1  is an isometric view of a first pressure surge sensor embodying the invention, with the housing body of the sensor cut away, to show the interior parts. 
           [0022]      FIG. 2  is an end view on the left hand end of the pressure surge sensor of  FIG. 1 . 
           [0023]      FIG. 3  is a side view of the pressure surge sensor of  FIG. 1 . 
           [0024]      FIG. 4  is an isometric view of a second pressure surge sensor embodying the invention, cut along an axial section, to show interior parts. 
           [0025]      FIG. 5  is a diagrammatic view of an assembly embodying the invention. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0026]    The pressure sensor embodying the invention shown in  FIGS. 1 to 3  has a body in the form of a housing  10 , which is made in one piece of suitable synthetic resin material, in the present case of nylon 6/6. Any other suitable non-magnetic material may be employed for this housing  10 . The housing  10  has a central passage  12  which has a large screw-threaded portion  14  at one end, suitable to make connection with a complementarily threaded pipe. Apart from this large opening end  14 , the central passage  12  is a circular-sectioned cylindrical shape passage  13  having a step  15  and extending to an open end  16  at the opposite end of the body  10 . 
         [0027]    On the exterior of the body  10 , there is mounted a magnetically actuated reed switch  17  of a standard design, containing electrical contacts which are biased towards an open position and held in the closed position when subjected to a magnetic field provided by a magnet described below. Electrical wires  18  are connected to the switch  16 , so that opening and closing of the contact in the switch  16  can be detected. 
         [0028]    In the cylindrical passage  13  of the housing  10  a piston  20  is located, also having a circular cross-section and closely fitting within the passage  13 , while being movable along the passage. At the first end of the piston  20 , towards the large portion  14 , there is mounted a felt washer  22  which is held in place by a steel disc  24  having openings through it and attached to the piston  20 . The felt washer  22  provides a better seal of the piston  20  to the surface of the passage  13 . A different form of piston ring may be provided to achieve a satisfactory seal between the piston  20  and the body  10 , or no additional seal may be provided. 
         [0029]    The piston  20  is made of a suitable synthetic resin material, in this case nylon 6/6, and holds within it a permanent bar magnet (not shown). 
         [0030]    In the position shown in  FIG. 1 , movement of the piston  20  to the right hand side is optionally prevented by a piston retainer  26  which is a graphite rod and is easily broken. The load required to break this retainer  26  is small. 
         [0031]    At the extreme right hand end of the passage  13  there is a fixed steel ring  28 , which is removable, and which prevents the piston  20  from being driven out of the passage  13 . On removal, it allows insertion and replacement of the piston  20 . 
         [0032]    As shown in  FIG. 1 , the piston is held against movement towards the open end  14  by the step  15  in the passage  13 . 
         [0033]    Spaced from the right hand side of the piston in its position shown in  FIG. 1 , the body  10  has laterally opening vents  30  extending from the passage  13  to the exterior peripheral face of the body  10 . 
         [0034]    Operation of the pressure surge sensor shown in the drawings is as follows. The normal rest position, before actuation of the sensor, is as shown in  FIG. 1 . In this position, the magnet within the piston  20  holds the contacts within the switch  16  in their closed position, allowing passage of current between the two wires  18 . Typically a control device of the apparatus, to which the pressure surge sensor is fitted, continuously or periodically checks that the current flows, the contacts remaining closed. The piston  20  is held in place between the piston retainer  26  and the step  15 . When a gas pressure surge having a pressure sufficiently above that of the atmosphere is applied at the end  14 , the piston  20  is driven to the right as shown in  FIG. 1  by the pressure differential over atmospheric pressure, breaking the retainer  26  and moving along the passage  12  at least until the vents  30  are uncovered, when excess pressure in the passage  12  can escape into the atmosphere. This movement of the piston  20  changes the magnetic field applying at the switch  16 , allowing the contacts within the switch  16  to open, breaking the electrical connection between the two wires  18 . This is sensed by the control device of the apparatus mentioned above, so that suitable action can be taken. A warning signal may be generated and/or the apparatus may be, for example, shut down. 
         [0035]    After breakage of the optional retainer  26 , no mechanical element provides a driving force opposing movement of the piston  20  along the passage  12 . Only friction provides resistance to movement. 
         [0036]    When used in conjunction with a rupture disc, the pressure surge sensor is connected, via the screw threaded opening end  14 , to a pipe structure in which the rupture disc is mounted. The pressure surge sensor is thus on the downstream or low pressure side of the bursting disc. When the rupture disc operates by rupture, when its bursting strength is exceeded, a pressure surge passes through the bursting disc and operates the pressure surge sensor as described above. The rupture of the rupture disc is therefore detected. 
         [0037]    For example, when the rupture disc is arranged in an extrusion machine, e.g. on a branch pipe connected to the pressurized chamber of the extrusion machine, or when the rupture disc is arranged connected in a gas handling or storage system to detect overpressure, the rupture disc is selected so as to rupture at the desired maximum operating pressure of the machine or system. Rupture of the rupture disc when this pressure is exceeded is detected by the pressure surge sensor. Operation of the pressure surge sensor is detected by the control device of the machine, which causes the machine to cease operation. 
         [0038]    The pressure surge sensor is simple in operation, and is reliable, since the piston is able to move when subjected to a relatively low pressure differential. The device is not integral with the rupture disc mounting, and is easily mounted to an existing structure or incorporated in a new assembly. 
         [0039]    The contacts of the switch  16  may alternatively be held in the open position by the magnetic field of the magnet in the piston  20 , but the arrangement described above is more fail-safe because accidental cutting of the wire  18  is detected. In another embodiment, the switch  16  may be mounted at a different position on the body  10 , so that the magnet  20  can moves past it or comes to a stop close to it, when the pressure surge causes movement of the magnet. 
         [0040]    The device can be made of components which are capable of resisting relatively high temperatures, for example 100° C. 
         [0041]    In the drawings, the cylinder passage  12  and the piston  20  are circular in cross-section, which is most convenient, but may be of other cross-section shape. 
         [0042]      FIG. 4  shows a pressure surge sensor embodying the invention which is a modification of the sensor of  FIGS. 1 to 3 . Similar or identical parts are identified by the same reference numbers and will not be described again. This sensor differs from that of  FIGS. 1 to 3  in several ways. Instead of the removable ring  29 , the body  10  has an integral end  28   a  having a small hole  28   b  through it to allow air to escape. The piston  20  cannot be removed at this end of the body  10 . At the left end in  FIG. 4 , the body  10  has a pipe portion  10   a  screw-threadedly engaged into the body  10  and providing an abutment face  10   b  which prevents the piston  20  from moving to the left from its normal rest position adjacent the optional breakable retainer  26 . The pipe portion  10   a  has a connector  10   c  screw-threadedly engaged on it and having an exterior screw-thread  10   d  which is suitable for connection to a pipe or other vessel in which the pressure surge, to be detected, may occur. Removal of the pipe portion  10   a  from the body allows insertion, removal and replacement of the piston  20 . 
         [0043]    The operation of the sensor of  FIG. 4  is the same as that of  FIGS. 1 to 3 . 
         [0044]      FIG. 5  shows diagrammatically an assembly of the invention, comprising the sensor of  FIG. 4  indicated by reference numeral  11 , a rupture disc assembly  1  and a wall of a pressurized apparatus, schematically indicated by reference numeral  9  having an internal face  9   a  at the high-pressure side and an external face  9   b . The pressurized apparatus  9  is for example a conventional extrusion apparatus, e.g. for extrusion of plastics or metal, or is a pressurized tank or other vessel of a gas handling or gas storage system. 
         [0045]    Attached to the front end of the body  10  of the sensor  11 , by a screw-thread, is a tubular member  6  replacing the elements  10   a  and  10   c  of  FIG. 4 . The member  6  holds the disc unit having the disc  2  at its distal end and is sealingly engaged in a bore  7  through the wall  9  by a screw-thread  8 . 
         [0046]    The rupture disc assembly  1  shown is of a known type, such as described in GB-A-2285284, WO03/031853, WO2005/054731, WO2007/036719 and EP-A-1938007. The assembly  1  has a forward-acting rupture disc unit having a rupture disc  2  adapted to rupture at a predetermined pressure at the interior of the wall  9   
         [0047]    When excess pressure in the pressurized apparatus  9 , being protected by the rupture disc assembly  1 , is applied to the inlet face of the disc  2 , the disc  2  ruptures, releasing a pressure surge along the central bore  6   a  of the member  6  to the pressure surge sensor  11 , which provides an electrical output signal, which may act as a warning and/or be used for control of the apparatus  9 . 
         [0048]    While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.