Abstract:
A pressure indicating device for detecting and isolating leakage of toxic and/or pyrophoric gasses from within various packages is disclosed. The device can affix to a user port of a cylinder package. The device has a flexible disc-like structure which is fine tuned to outwardly flex in response to a build-up of pressure of the gas exerted against the disc-like structure. The flexed disc contacts a movable pin and pushes the push outwards from within the device. The outward movement of the pin pierces a paper seal extending over the device, thereby indicating a leak from within the valving of the package. The device withstands the pressure exerted against it, thereby also isolating the leak of the pressurized gas.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a pressure indicating device to be attached to a user port of various gas packages. The device is capable of visually indicating a valve leak and isolating the leak to prevent any material inside the cylinder from escaping. 
       BACKGROUND OF THE INVENTION 
       [0002]    Industrial processing and manufacturing applications, such as semiconductor manufacturing, typically require the safe handling of toxic, corrosive and/or flammable hydridic and halidic gases and mixtures thereof. By way of example, the semiconductor industry often relies on the gaseous hydrides of silane (SiH 4 ), and liquefied compressed gases such as arsine (AsH 3 ) and phosphine (PH 3 ) for wafer processing. Various semiconductor processes utilize SiH 4 , AsH 3  or PH 3  from vessels that have storage pressures as high as 1500 psig. As a result of their extreme toxicity and/or pyrophoricity and high vapor pressure, uncontrolled release of these gases, which can occur due to delivery system component failure, or human error during cylinder change-out procedures, may lead to catastrophic results. For example, the release of a flammable gas such as silane may result in a fire, system damage and/or potential for personal injury. Leaks of a highly toxic gas, such as arsine, could result in personal injury or even death. 
         [0003]    A pyrophoric gas such as silane after filling into a package, is attached with an outlet cap. However, internal leakage of silane across the valve seat can accumulate within a dead space volume behind the outlet cap. When the cap is removed, the leaked silane can emerge from the user port and come into contact with air, resulting in a “popping” sound. The popping sound can be accompanied by a flame in the user port. Relatively smaller silane leaks may give no visual indication of a leak, but yet can result in a popping sound when the silane comes into contact with air. The popping can also be accompanied by a flame in the user port. 
         [0004]    The internal leakage of silane across the valve seat can occur during the transport of silane cylinders, during which sufficient momentum can be imparted to the valve seat causing it to momentarily open and then reseat. This momentary opening of the valve seat is known as “burping” in the industry, and can put sufficient pressure under the outlet cap, such that popping can occur when the cap is removed. Burping can be a particular problem with spring-loaded pneumatic valves. 
         [0005]    Additionally, silane can oxidize to form silicon dioxide white particulates, which can then deposit on the valve seat. By virtue of the deposited particles, the valve can no longer make a leak-tight seal when the valve is closed, thereby resulting in leakage across the port (known as cross porting in the gas industry). 
         [0006]    There is an unmet need to improve the safety of silane packages. Other aspects of the present invention will become apparent to one of ordinary skill in the art upon review of the specification, drawings, and claims appended hereto. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention is directed to a pressure indicating device affixed to a user port of a pressurized cylinder. The device has a flexible disc-like structure which can be fine tuned to outwardly flex in response to a build-up of pressure of the gas exerted against the disc-like structure. The flexed disc contacts a movable pin and pushes the pin outwards from within the device. The outward movement of the pin pierces a seal extending over the device, thereby visually indicating an internal leak across a valve seat from within the valve of the cylinder. The device is designed to provide such an indicator only when dangerous levels of gas have internally leaked within the cylinder. In this manner, the visual indicator notifies an operator to not remove the device from the user port, and to not use the cylinder for delivery of gas contained within the cylinder. The device withstands the pressure exerted against it, thereby also isolating the leak of the pressurized gas. 
         [0008]    The invention may include any of the following aspects in various combinations and may also include any other aspect described below in the written description or in the attached drawings. 
         [0009]    In a first aspect of the invention, a pressure indicating device for recording and isolating a leak of pressurized gas from a closed valve of a gas cylinder is provided. The pressure indicating device comprises a housing defined, in part, by an upper housing portion and a lower housing portion, the upper housing portion characterized by an inner channel extending therethrough, and the lower housing portion characterized by a gas flow channel extending therethrough. The lower housing portion is disposed within a user port of the cylinder valve. A movable pin is disposed within the interior channel of the upper housing portion. A solid diaphragm in a neutral state is disposed between the upper and the lower housing portions. The diaphragm has a bottom surface and a top surface. The top surface of the solid diaphragm is oriented towards the pin, and the bottom surface of the solid diaphragm is oriented towards the lower housing portion, wherein the bottom surface is in fluid communication with the gas flow channel. The diaphragm is sealed in place along an edge thereof. A seal is provided that extends along an outer surface of the upper housing through which the pin is configured to extend when said pin is in the activated state. The solid diaphragm is configured to flex from a neutral state to an activated state towards the pin in response to a predetermined activating pressure exerted against at least a portion of the bottom surface of the diaphragm. The diaphragm in the activated state flexes a sufficient amount against the pin so that a portion of the top surface of the diaphragm urges the pin from within the inner channel a sufficient axial distance through the upper housing so as to move the pin externally of the housing, thereby allowing the pin to pierce the material and visually indicate the leak of the pressurized gas from within the interior volume of the cylinder. 
         [0010]    In a second aspect of the invention, a safety system for isolating and indicating a leak of pressurized gas is provided. The system comprises a cylinder for holding a pressurized gas; a user pathway defined in part by a valve body affixed to an upper part of the cylinder; a pressure indicating cap having an upper housing and a lower housing mated thereto, the lower housing threadably engaged within the user pathway of the cylinder, the lower housing having a gas flow channel configured to receive a flow of the pressurized gas; the cap further comprising a disc disposed between the upper housing and the lower housing, the disc having a periphery fixably attached to corresponding edge portions of the upper and the lower housing; —a movable pin situated within the upper housing, the pin spaced apart a predetermined distance from the top surface of the disc; wherein the top surface of the disc is configured to flex from a neutral state towards the pin in response to a predetermined accumulation of pressure within the gas flow channel that is exerted against the bottom surface of the disc, the top surface of the disc flexed a sufficient amount to exert a force that pushes the pin outwardly from the upper housing in an axial direction so as to record a pressure leak. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The objects and advantages of the invention will be better understood from the following detailed description of the preferred embodiments thereof in connection with the accompanying figures wherein like numbers denote same features throughout and wherein: 
           [0012]      FIG. 1   a  shows a pressure indicating device incorporating the principles of the invention whereby the device is attached to a lateral port of a valve body; 
           [0013]      FIG. 1   b  shows a cross-sectional view of a valve having a lateral user port into which the pressure indicating device of the present invention can engage therewithin; 
           [0014]      FIG. 2   a  shows a cross-sectional view of the device of  FIG. 1   a , whereby the device is in a neutral state; 
           [0015]      FIG. 2   b  shows a cross-sectional view of the device of  FIG. 1   a , whereby the device is in an activated state; 
           [0016]      FIG. 3  shows a perspective view of the pressure indicating device of the present invention of  FIGS. 1 and 2 ; and 
           [0017]      FIG. 4  shows components prior to assembly of the pressure indicating device of the present invention in accordance with principles of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    The present disclosure relates to a pressure indicating device. The disclosure is set out herein in various embodiments and with reference to various aspects and features of the invention. 
         [0019]    The relationship and functioning of the various elements of this invention are better understood by the following detailed description. The detailed description contemplates the features, aspects and embodiments in various permutations and combinations, as being within the scope of the disclosure. The disclosure may therefore be specified as comprising, consisting or consisting essentially of, any of such combinations and permutations of these specific features, aspects, and embodiments, or a selected one or ones thereof. 
         [0020]      FIG. 1   a  shows one embodiment of a pressure indicating device  100  in accordance with principles of the present invention. The device  100  is shown attached into lateral user port  108  of a manual valve body  101 . A cross-sectional view of a pneumatic valve body  101  into which the device  100  can be inserted is shown in  FIG. 1   b . Threads located along the bottom housing  106  ( FIG. 1   a ) of device  100  can threadably engage and mate with threads along the user port  108 . The threaded portion ( FIG. 1   a ) of valve body  101  can affix to the top of a cylinder body. 
         [0021]    In the event that pressurized gas stored within the cylinder leaks across a valve seat  111  ( FIG. 1   b ) of the valve body  101 , gas can accumulate within a dead space volume  112  ( FIG. 1   b ) adjacent to the device  100 , thereby causing the pressure to a rise up to the fill pressure of the cylinder. 
         [0022]      FIGS. 2   a  and  2   b  show the pressure indicating device  100  of  FIGS. 1   a  and  1   b  in cross-sectional view, whereby the device  200  is shown in a neutral state and an activate state, respectively. It should be appreciated by one skilled in the art that that all of the elements of the device  100  of  FIGS. 1   a  and  1   b  are incorporated into  FIGS. 2   a  and  b . As a result, the elements and features of the device  200  shown in  FIGS. 2   a  and  2   b  should be understood in relation to the elements and features shown in  FIGS. 1   a  and  1   b.    
         [0023]    With reference to  FIGS. 2   a  and  2   b , the rise in pressure is exerted against a flexible diaphragm  206  of the device  200 . Generally speaking, and as will be explained in greater detail, the device  200  includes a movable pin  204  that is designed to be urged outwards by a flexible diaphragm  206  in response to the pressure. As the pin  204  axially extends outwards, it pierces material  213  disposed over the top housing  201 , as shown in  FIG. 2   b . The pin  204  remains extended in a so-called “activated state” as the device  200  isolates and contains the pressure, thereby preventing the pressurized gas from leaking beyond device  200 . The extended pin  204  and pierced material  213  serve as a visual indicator of the existence of elevated levels of gas leakage across the valve seat  111  and into the user port  108 . In this manner, an operator can see that the cylinder has an unacceptable gas leak that is not suitable for use. The ability of the device  200  to isolate a leak of pressurized gas as well as record such a leak prior to cylinder use provides an enhanced level of safety. 
         [0024]      FIGS. 2   a  and  2   b  show device  200 , which represents the device  100  of  FIG. 1  in cross-sectional view. It should be appreciated by one skilled in the art that the elements of  FIG. 1  are incorporated into  FIGS. 2   a  and  2   b . As a result, the elements and features of the device  200  shown in  FIG. 2  should be understood in relation to the elements and features shown in  FIG. 1 . 
         [0025]      FIG. 2   a  shows a cross-sectional view of the device  200  in the relaxed state. The relaxed state as used herein and throughout the specification is defined by the absence of gas leakage or, in the alternative, the absence of gas leakage in an amount sufficient to create a pressure against the flexible diaphragm  206  of the device  200  that urges the movable pin  204  outwards from within the top housing  21 . The terms “relaxed” and “neutral” will be used interchangeably throughout the specification and are intended to have the same meaning of a cylinder in a safe state. 
         [0026]      FIG. 2   a  shows the movable pin  204  configured in a relaxed state. The pin  204  is entirely disposed within the top housing  201 . The tip of the pin  204  is shown below the material  213  and entirely within the top housing  201 . Preferably, the tip is not in contact with the material  213  when the pin  204  is in the relaxed state to avoid inadvertent perforation of the material  213 . The pin  204  is shown with no threads to enable it to controllably slide within the top housing  201 . A spring  203  is shown coiled around the base of the pin  204 . The coiled spring  203  exerts a slight downward force against the pin  204  to prevent inadvertent extension of the pin  204  when in the relaxed state. In one example, the spring  203  may be set between 1-10 psi to prevent the pin  204  from moving in the relaxed state. 
         [0027]    The diaphragm  206  resembles a disc-like structure which can be formed from any suitable material, including spring steel or other metal alloys. The diaphragm  206  is configured to flex and urge the pin  204  outwards from the top housing  201  when sufficient leakage of gas across the valve seat  111  and into the user port  108  ( FIG. 1   b ) occurs. The leaked gas thereafter flows through gas channel  217  of device  200  and terminates into the reservoir  208 , where pressure can rise to a predetermined activating pressure sufficient to flex the diaphragm  206  upwards into a dome-like structure, as shown in  FIG. 2   b , so that the device  100  acquires a flexed or activated state. The terms “flexed” and “activated” as used herein are intended to have the same meaning and will be used interchangeably throughout the specification. 
         [0028]      FIGS. 2   a  and  2   b  show that the diaphragm  206  is disposed between the upper and the lower housing portions  201  and  207 , respectively. The diaphragm  206  has a bottom surface  231  and a top surface  230 . The top surface  230  is configured so as to face towards the pin  204 .  FIG. 2   a  shows a predefined gap  235  exists between the top surface  230  and the bottom of the pin  204  to enable the diaphragm  206  to flex upwards towards the pin  204 . The bottom surface  231  of the diaphragm  206  faces in a direction towards the lower housing portion  207 . The bottom surface  231  is preferably substantially abutted against the lower housing  207  in the relaxed state ( FIG. 2   a ). The edges  236  and  237  of the diaphragm  206  are sealed in place between the top housing  201  and the lower housing  207 . In one embodiment, the edges  236  and  237  are sealed by welding a bead around the entire perimeter of the device  100 . Welding can be performed using an orbital welder as known in the art. The thickness of the bead is preferably equal to or greater than the wall thickness of the top housing  201 . The edges  236  and  237  are therefore sealed and remain stationary at all times (i.e., during the relaxed state of  FIG. 2   a  and the activated state of  FIG. 2   b ) to prevent gas from flowing outwardly beyond the reservoir  208  and potentially leaking beyond the edges  236  and  237  and out from the device  200 . The portions of the diaphragm  206  inward of the edges  236  and  237  are not attached or affixed to any surfaces of the top housing  201  or bottom housing  207 , thereby allowing the diaphragm  206  to flex. The bottom surface  231  is in fluid communication with reservoir  208  and gas flow channel  217 . 
         [0029]    In the event of a leak across valve seat  111  ( FIG. 1   b ) and into the user port  108  ( FIG. 1   b ), gas stored within the interior of a cylinder may flow into gas channel  217  and accumulate within reservoir  208 . The reservoir  208  may have any cross-sectional shape. In the embodiment of  FIG. 2   a  and  FIG. 2   b , the reservoir  208  is rectangular-shaped. The reservoir  208  is designed to have a predetermined volume that is preferably larger in cross-section than the cross-section of gas channel  217  to allow a sufficient build up of pressure to an activating pressure therewithin that adequately flexes the diaphragm  206  to urge the pin  204  axially upwards beyond the top housing  201 . 
         [0030]      FIG. 2   b  shows that as gas continues to accumulate within reservoir  208 , the pressure rises to a predetermined threshold or activating pressure which causes the diaphragm  206  to flex upwards into the predefined gap  235 . The diaphragm  206  undergoes a change in configuration and transitions from the relaxed state of  FIG. 2   a  to the flexed state of  FIG. 2   b . The top surface  230  of the flexed diaphragm  206  pushes against the pin  204 . The diaphragm  206  urges the pin  204  from within the top housing causing the pin  204  to protrude through the top housing  201  and pierce material  213 . The pierced material  213  and axially extended pin  204  visually indicate a leakage of gas across the valve seat  111 . In a preferred embodiment, when the gas stored is silane, the leakage has occurred at dangerous levels which may result in silane popping if the device  200  is removed from the valve body  101 . Accordingly, the pressure indicating device  200  of the present invention can significantly reduce the risk of silane popping by notifying an operator not to remove the device  200  from the user port  108  of the cylinder. 
         [0031]    Surrounding or stabilizing material  218  is sufficiently rigid to stabilize, support and maintain the diaphragm  206  in the final flexed configuration shown in  FIG. 2   b . Material  218  is sufficiently rigid to remain stationary when diaphragm  206  transitions from the relaxed state to the activated state. The specific type of material  218  is selected to prevent the diaphragm  206  from continuing to have a tendency to excessively flex, thereby preventing diaphragm  206  from potentially rupturing. In this manner, the material  218  provides structural support to the flexed diaphragm  206  and maintains diaphragm  206  in the flexed position. The material  218  allows diaphragm  206  to isolate the pressurized gas within the reservoir  208 . Should the pressure exerted against the bottom surface  231  of diaphragm  206  increase, the surrounding material  218  will possess sufficient rigidity to counteract such pressure increase, thereby preventing the flexed diaphragm  206  from further having a tendency to flex and/or axially move upwards. The combination of diaphragm  206 , surrounding material  218  and other components of device  200  are designed and constructed to preferably hold a maximum pressure equal to about 5/3 of the cylinder rating pressure. 
         [0032]    Additionally, the specific type of surrounding material  218  selected is preferably rigid enough to limit the maximum axial distance of the diaphragm  206 . Commercially available Delrin® resins and other suitable commercially available plastics known in the art may be utilized in the present invention to impart the necessary rigidity. 
         [0033]      FIG. 2   a  shows that in addition to the predefined gap  235  between the bottom of the pin  204  and the diaphragm  206 , a predefined gap  286  is present between the bottom of the surrounding material  218  and the diaphragm  206  in the relaxed state. The predefined gap  286  is created by virtue of the bottom of the surrounding material  218  tapering inward from edges  236  and  237  to each of the sides of the pin  204 , as shown in  FIG. 2   a . The predefined gap  286  permits the diaphragm  206  to axially move as it flexes and can represent the maximum axial distance the diaphragm  206  flexes. The diaphragm  206  to flex and axially move the necessary distance to urge pin  204  outwards through material  213 , in response to the activating pressure (i.e., the pressure at which device  200  visually indicates unacceptable leakage levels of gas across the valve seat  111  by pin  204  piercing material  213 ). The diaphragm  206  can continue to flex upwards until it contacts the surrounding material  218 . When the diaphragm  206  flexes upwards and abuts against the surrounding material  218 , the gas pressure against the bottom surface  231  of the diaphragm  206  is counteracted by the downward pressure exerted against the top surface  230  of the diaphragm  206  by surrounding materials  218 . The diaphragm  206  acquires a final flexed position in which the diaphragm  206  substantially remains until the activating pressure against the bottom surface  231  is removed. The predefined gap  235  between the diaphragm  206  and pin  204  and the predefined gap  286  between the diaphragm  206  and surrounding material  218  have both reduced to substantially zero. Such a reduction in each of gaps  235  and  286  is associated with a corresponding increase in the volume of reservoir  208 , as shown in  FIG. 2   b.    
         [0034]    Still referring to  FIG. 2   a , the pin  204  in the relaxed state may be spaced apart a predetermined gap  290  from surrounding material  218 . When pin  204  is urged by diaphragm  206  in response to an activating pressure, the pin  204  can axially move upwards a distance equal to the gap  290 . The distance of gap  290  is designed to ensure the tip of pin  204  can extend beyond the top housing portion  201  and pierce material  213  when the diaphragm  206  flexes. 
         [0035]      FIG. 3  shows device  300 , which represents the device  200  of  FIG. 2  in perspective view. Bottom housing  307  has sealing members which prevents leakage of gas across the device  200 . Specifically, a sealing member  310  and sealing gasket  339  are shown along the bottom housing  307 . The sealing member  310  and sealing gasket  339  engage within lateral port  108  of valve body  101  ( FIG. 1   b ) to enable internally leaked gas (i.e., gas that has flowed across valve seat  111 ) from flowing beyond device  300  and being released to the atmosphere. Threads  340  can threadably engage onto complimentary threads along lateral port  108  of valve body  101 . It should be understood that other variations as known in the art for creating sealing surfaces between device  300  and valve body  101  are contemplated. 
         [0036]    The criteria for designing a suitable device  200  in accordance with the embodiments shown in  FIGS. 1   a ,  1   b  and  FIGS. 2   a ,  2   b  may be dependent upon various parameters. For example, the design of the device  200  would preferably take into account several parameters, including determining the minimal activating pressure within reservoir  208  at which elevated levels of leaked gas would be considered toxic or could cause a small fire or popping noise if released to the atmosphere. In one embodiment, the activating pressure at which the diaphragm  206  should be designed to flex and urge the pin  204  outwards to pierce material  213  can range from about 10 psi up to about the maximum pressure of the cylinder. 
         [0037]    Still further, the design of a suitable diaphragm  206  should also take into consideration the type of gas being supplied. The type of gas stored can affect the required thickness of the diaphragm  206 . A low pressure exerted against the bottom surface of the disc  231  may require a relatively thinner diaphragm  206  to be employed. For example, gases such as arsine are liquefied gases, having a pressure limited by their vapor pressure. Arsine exerts a vapor pressure of approximately 200 psig at 70° F. Because such a relatively low supply pressure exerts a small amount of pressure at the bottom surface  231  of the diaphragm  206 , a thinner and less stiff diaphragm  206  more prone to flexing may be preferable, as even relatively low concentrations of released arsine into the atmosphere would be considered hazardous. 
         [0038]    Other gases, which are filled into cylinders at pressures of 1250 psig or higher and which may be less hazardous, may potentially require a thicker more rigid diaphragm  206  to avoid premature flexing of the diaphragm  206  that would visually indicate a false positive. In another embodiment, if the gas being stored within a cylinder is silane, the diaphragm  206  may be configured to flex in response to an activating pressure within reservoir  208  that corresponds to a certain number of grams of leaked silane sufficient to cause silane popping. The pressure indicating device of the present invention can be uniquely identified to ensure it is attached and used with the intended cylinder. In this manner, inadvertent attachment of, for example, a high pressure indicating device to a low pressure cylinder or vice versa can be avoided. In one example, the pressure indicating device can be color coded to that of its corresponding cylinder for which it is intended. 
         [0039]    Selection of a suitable material for diaphragm  206  can include spring steel, metal alloys and the like. Different materials will require different thicknesses to flex at a predetermined activating pressure for a particular gas having a defined pressure within cylinder. Accordingly, the thickness of the disc and the rigidity or strength of the disc are preferably also taken into account along with material selection. 
         [0040]    Design of the diaphragm  206  can also taken into consideration the net effective volume of the reservoir  208  into which leaked gas accumulates prior to the diaphragm  206  flexing. The size of the cylinder may also be taken into account. Still further, other design considerations may include the distance the disc is required to flex before contacting pin  204  (i.e., denoted as predetermined gaps  235  and  236  in  FIG. 2   a ). An optimal design of the device  200  will involve balancing the aforementioned design parameters to allow the diaphragm  206  to selectively flex in response to a predetermined activating pressure. The aforementioned parameters interact with each other to determine the final design and construction of the diaphragm  206  and overall device  200 . 
         [0041]    Designing and constructing the diaphragm  206  to selectively flex within a specific pressure range ensures that cylinders are removed from service by an operator only when necessary. A build up of pressure below the activating pressure may still allow removal of the device  100  from the cylinder user port  108  if determined that the leaked gas from cylinder would be released to levels which are not dangerous and/or which are released at levels that are diluted to a virtually safe level. The ability of the device  200  to be tuned to a specific activating pressure to provide such visual indications can therefore avoid false positives. 
         [0042]    Numerous techniques can be employed for constructing device  100 . One possible means for the construction of the device  100  of the present invention can be better understood in relation to  FIG. 4 , which shows the spatial arrangement of components relative to each other prior to their assembly. The stabilizing material  418 , the pin  404  and the diaphragm  406  are assembled so as to be contained within the top housing  401 . The pin  404  is slightly tensioned to a few psig with an accompanying spring  403  helically coiled around the pin  404 . In this manner, the spring  403  prevents the pin  404  from inadvertently moving towards the top housing portion  401  and piercing material  413  in the neutral or relaxed state to generate a false positive reading. 
         [0043]    Furthermore, although not visible in  FIG. 4 , a gradual taper can be created from each of the edges of the stabilizing material  418  to the sides of the pin  404 , as shown in  FIG. 2   a , to create the necessary gaps for diaphragm  406  to flex in response to an activating pressure. 
         [0044]    A gasket  405  may be optionally disposed between the bottom of the pin  404  and the top surface  430  of the diaphragm  406  to ensure adequate contact between the diaphragm  406  and the pin  404 . Gasket  405  creates a gap  235  that is designed to prevent an electrical contact between pin  204  and top surface  230 . In this manner, no electrical conductivity exists between pin  204  and top housing  201  in the neutral state. Conversely, in the activated state, electrical conductivity exists between the pin  204  and the top housing  201 . The gasket  405  may be optional if only a small pin displacement has occurred. Leaked gas extends in an upwards direction (as shown by the arrow in  FIG. 4 ), through gas channel  417  and thereafter terminates into a reservoir  408 . The reservoir  208  as shown in  FIGS. 2   a  and  2   b  is created after the bottom surface  431  of the diaphragm  406  has been sealed onto the lower housing portion  407 . Specifically, the reservoir  208  is defined by the bottom surface  431  of the diaphragm  406 , the indented surface  408  of the bottom housing portion  407  and the periphery of the indented surface  408 . The edges of the diaphragm  406  along its top surface  430  are welded to the top housing portion  401  and the edges of the diaphragm  406  along its lower surface  431  are welded to the lower housing portion  407  thereby creating a seal along the periphery of the device  400 . The weld preferably extends completely around the periphery of the top surface  430  and bottom surface  431  of diaphragm  406 . The weld bead preferably has a thickness equivalent to at least a portion of the wall thickness of the top housing portion  401  and the lower housing portion  407 . The welds are sufficiently strong to withstand pressure of the leaked gas within reservoir  408 . The remainder of the diaphragm  406  remains unwelded to allow it to flex in response to a predetermined activating pressure, as shown in  FIG. 2   b.    
         [0045]    The top housing portion  401  may contain an opening along its top-most surface for material  413  to be affixed. The lower housing portion  407  can be machined to specific dimensions which will match the corresponding dimensions of lateral port  108  of valve body  101  ( FIG. 1   b ). Final assembly of the components of  FIG. 4  preferably occurs by welding. 
         [0046]    The pressure indicating device of the present invention as has been described advantageously allows cylinders to be removed from service before removing the device and exposing an operator to dangerous levels of gases at the user port  108 . Silane pops can be avoided when the pressure indicating device of the present invention has visually indicated an extended pin through pierced material. Because the device remains affixed to the valve body of the cylinder and the pin is protruding through pierced material, the pin does not revert back into the top housing portion of device. The visual indicator is therefore permanent and notifies the operator to remove the cylinder from the production area. The unsafe cylinder can be returned to the factory where personnel can wear protective equipment and perform standard safety handling procedures during removal of device. After the device is removed from the user port of cylinder, a waste line can be connected in which the valve of the cylinder is opened to safely transfer the gas to a scrubber or another cylinder. 
         [0047]    Other design alternatives may be employed to achieve a predetermined flexing of the diaphragm. In an alternative embodiment, the pressure indicating device does not contain a reservoir into which the leaked gas accumulates. Rather, when the diaphragm of the device initially flexes upwards, the surface area of the bottom surface of the diaphragm that the leaked gas pushes against increases, thereby allowing continued flexing until the complete activated state has been achieved. 
         [0048]    Although the present invention has been described in reference to leaks within cylinders, it should be understood that the present invention can be employed in any suitable high pressure storage and delivery package. Furthermore, the pressure indicating device may be used in combination with other devices, such as, for example, a pressure relief valve. 
         [0049]    Although the present invention can eliminate the occurrence of silane pops, the present invention can also be useful as an pressure indicating device to detect dangerous levels of toxic gases which are not pyrophoric but which will visually indicate to an operator that the cylinder contains a toxic amount of gas behind the device such that the device should not be removed to expose the user port. 
         [0050]    While it has been shown and described what is considered to be certain embodiments of the invention, it will, of course, be understood that various modifications and changes in form or detail can readily be made without departing from the spirit and scope of the invention. It is, therefore, intended that this invention not be limited to the exact form and detail herein shown and described, nor to anything less than the whole of the invention herein disclosed and hereinafter claimed.