Abstract:
A level indicator for a container that is lined with a membrane for holding fluid, and which has a wall with an aperture formed through it. A frame is attached to the container wall adjacent to the aperture. A plunger is engaged with the frame, and moves between an extended position, where the plunger extends through the aperture and into the interior of the container, and a retracted position, where the plunger does not substantially extend into the interior of the container. An elastic member between the frame and the plunger urges the plunger to the extended position. A visual indicator is driven by the plunger between an indicating position and a non-indicating position. The force of the elastic member is selected to enable the membrane, under static pressure of fluid within the container, to urge the plunger to the retracted position.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates fluid level indicators. More particularly, the present invention relates to fluid level indicators useful in conjunction with rigid containers having flexible liners for storing or processing liquids or other fluid materials. 
     2. Description of the Related Art 
     Storage and processing containers are in widespread use in various industries and other endeavors. Many of these are used to contain liquids and other flowable bulk materials, such as powders and granular materials. While containing many types of fluid materials, it is preferable to line the container with a polymeric membrane so that the bulk material is either impermeably contained in a suitable polymeric material, or to insure that the bulk materials does not contact the container itself. For example, in the case of pharmaceutical and food grade materials, a polymeric liner, such as PVC or polypropylene, may be used to maintain the purity and cleanliness of the bulk material. In other instances, the bulk material may react with a storage container itself, so a polymeric liner is used to prevent such reactions. 
     Various fluid level indicators are known and used with liquids and other bulk fluid materials. Most level indicators sense fluid level using some form of direct contact with the contained bulk material. For example, the classic floating level indicator is commonly used in fuel tanks Another classic example is the liquid sight gauge, where the contained liquid level is visually presented through a transparent portion of the gauge. Other fluid level indicators use more sophisticated detection techniques, including acoustic detection, proximity detection, mass, pressure and so forth. However, these more sophisticated techniques are generally complex, expensive, and somewhat unreliable over time unless maintained by skilled technicians. 
     In the case where an impermeable liner is placed between a rigid container and a bulk fluid material being stored or processed therein, the challenges associated with the task of fluid level indication are increased. The operation of devices such as float gauges, sight glasses, and other direct contact system are interfered with by the liner membrane. Plumbing connections are more challenging, and would reduce system reliability and performance if attempted. Electronic fluid level detection devices can be interfered with as well. Thus it can be appreciated that there is a need in the art for an apparatus for indicating the fluid level in a lined container that overcomes the challenges associated with prior art designs. 
     SUMMARY OF THE INVENTION 
     The need in the art is addressed by the teaching of the present disclosure. The present disclosure teaches a level indicator apparatus for use with a container with an interior that is lined with a membrane for holding fluid, and which has a wall with an aperture formed into to. The apparatus includes a frame for attachment to the container wall adjacent to the aperture. A plunger is engaged with the frame, and is movable between an extended position, where the plunger extends through the aperture and into the interior of the container, and a retracted position, where the plunger does not substantially extend into the interior of the container. An elastic member is disposed between the frame and the plunger, and is oriented to deliver a force to urge the plunger to the extended position. A visual indicator is driven by the plunger between an indicating position and a non-indicating position. The force of the elastic member is selected to enable the membrane, under static pressure of fluid within the container, to urge the plunger to the retracted position. 
     In a specific embodiment of the foregoing apparatus, the container is a food grade or pharmaceutical grade process bin, and the membrane is a impermeable liner for the storage bin. In another embodiment, the membrane is a replaceable polymeric liner. 
     In a specific embodiment of the foregoing apparatus, the container wall may be an insulated wall or a clad wall, and the frame and the plunger are proportioned to accommodate additional thickness of the container wall. 
     In a specific embodiment of the foregoing apparatus, the frame is fabricated from a tubular stock material, and the plunger is movable within, and guided by, the tubular stock material. In a refinement to this embodiment, the tubular stock material is round stainless steel. In another specific embodiment the frame includes a flange that can be fastened to the wall around the aperture. 
     In a specific embodiment of the foregoing apparatus, the plunger is fabricated from a polymeric material. In another embodiment, the plunger has a distal face portion that engages the membrane, and that distal face portion is smooth and rounded to reduce possible damage to the membrane. 
     In a specific embodiment of the foregoing apparatus, the elastic member is a spring. In a refinement to this embodiment, the spring can selected from a compression spring, a tension spring, or other spring types know to those skilled in the art. In another specific embodiment, the spring couples the force to the plunger through a linkage. In a refinement to this embodiment the linkage is a lever. 
     In a specific embodiment of the foregoing apparatus, the visual indicator has a visual cue portion, and the visual cue portion is visible in the indicating position, but the visual cue portion is concealed in the non-indicating position. In a refinement to this embodiment, the frame conceals the visual cue portion in the non-indicating position. In another refinement, the visual cue portion is finished in a color that contrasts with the color of the frame. 
     In a specific embodiment of the foregoing apparatus, the plunger and the visual indicator are rigidly connected, and move in unison. In another embodiment, the plunger and the visual indicator are connected by a linkage. In anther embodiment, the plunger and the visual indicator are connected through a pivot. 
     The present disclosure also teaches a level indicator apparatus for use with a process bin, suitable for pharmaceutical product production, that has an impermeable polymeric liner for holding fluid inside, and which has a wall with an aperture formed through it. The apparatus includes a tubular frame with a flange to attach it to the process bin wall around the aperture. There is a plunger engaged within the tubular frame, which slides inside between an extended position, where the plunger extends through the aperture and into the interior of the storage bin, and a retracted position, where the plunger doesn&#39;t extend into the interior of the storage bin. The plunger has a distal face portion that engages the impermeable polymeric liner, and the distal face portion is smooth and rounded to reduce possible damage to the impermeable polymeric liner. A spring is disposed between the frame and the plunger, and oriented to deliver a force that urges the plunger to the extended position. A visual indicator is rigidly connected to the plunger so as to move in unison therewith, between an indicating position and a non-indicating position. The visual indicator having a visual cue portion, and the visual cue portion is visible in the indicating position, but the visual cue portion is concealed by the tubular frame in the non-indicating position. Also, the visual cue portion is finished in a color that contracts with the frame. In operations, the force of the spring is selected to enable the impermeable polymeric liner, under static pressure of fluid within the storage bin, to urge the plunger to the retracted position, thereby exposing the visual cue portion of the visual indicator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view drawing of a liquid container with plural level indicators according to an illustrative embodiment of the present invention. 
         FIGS. 2A and 2B  are exterior and interior views, respectively, of a level indicating apparatus according to an illustrative embodiment of the present invention. 
         FIGS. 3A and 3B  are exterior and interior views, respectively, of a level indicating apparatus according to an illustrative embodiment of the present invention. 
         FIGS. 4A and 4B  are exterior and interior views, respectively, of a level indicating apparatus according to an illustrative embodiment of the present invention. 
         FIGS. 5A and 5B  are exterior and interior views, respectively, of a level indicating apparatus according to an illustrative embodiment of the present invention. 
         FIG. 6  is a section view drawing of a pair of level indicators according to an illustrative embodiment of the present invention. 
         FIG. 7  is a section view drawing of a pair of level indicators according to an illustrative embodiment of the present invention. 
         FIG. 8  is a section view drawing of a pair of level indicators according to an illustrative embodiment of the present invention. 
         FIGS. 9A and 9B  are schematic diagrams of a level indicator apparatus in the retracted and extended positions, respectively, according to an illustrative embodiment of the present invention. 
         FIG. 10  is a schematic diagram of a level indicator apparatus according to an illustrative embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     Illustrative embodiments and exemplary applications will now be described with reference to the accompanying drawings to disclose the advantageous teachings of the present invention. 
     While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope hereof and additional fields in which the present invention would be of significant utility. 
     In considering the detailed embodiments of the present invention, it will be observed that the present invention resides primarily in combinations of steps to accomplish various methods or components to form various apparatus and systems. Accordingly, the apparatus and system components and method steps have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the disclosures contained herein. 
     In this disclosure, relational terms such as first and second, top and bottom, upper and lower, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms “comprises,” “comprising,” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by “comprises a” does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element. 
     An illustrative embodiment of the present invention is applied to the pharmaceutical industry, and in particular, processing bins that employ polymeric liners to impermeably retain a fluid content, which is commonly a liquid. Such processing and storage bins a commonly fabricated from stainless steel, for the benefits of corrosion resistance, cleanliness, and durability. As such, these bins are opaque and the contents are concealed from view. Although, it is known to provide a sight glass so that the interior can be partially viewed. However, the use of a sight class adds cost and reduced the durability of such bins. The polymeric liners are generally translucent to opaque, so that they reduce the effectiveness of a sight glass. Generally, the user would need to approach the sight glass and study it with care to ascertain and approximate liquid level. Also note that the polymeric liners are generally flexible bag-like structures that can be replaced from time to time. 
     Reference is directed to  FIG. 1 , which is a perspective view drawing of a liquid container  2  with plural level indicators  14 ,  16 ,  18  according to an illustrative embodiment of the present invention. This container  2  is an example of a fluid storage bin suitable for use in pharmaceutical processing and storage. The container  2  is fabricated with an exterior frame  4 , which comprises plural stainless steel structure shapes, such as rectangular tubing and angle iron shapes. The walls  6  are commonly fabricated from stainless steel sheet or plate stock. As such, the interior of the container  2  is smooth and suitable from housing a polymeric bag-type liner without risk for damage or puncture. This exemplary processing bin  2  comprises a pair of access doors  8 , which swing open  10  for access to the interior of the bin  2 . The top of a polymeric bag  12  is visible at the open top of the container  2 . As the polymeric liner  12  is filled and emptied, the unfilled portion of the polymeric bag moves upwardly and downwardly with the level of the liquid contained therein. Of course, the static pressure of the liquid displaces the polymeric liner  12  firmly against the walls  6  of the bin  2 . This figure illustrates the use of level indicators of the present invention, including two level indicators  14 ,  16  mounted in the wall  6  of the bin  2 , and one level indicator  18  installed in the door  8  of the bin  2 . The design and function of the level indicators will be more fully described hereinafter. 
     Reference is directed to  FIGS. 2A and 2B , which are exterior and interior side views, respectively, of a level indicating apparatus  25  according to an illustrative embodiment of the present invention.  FIG. 2  illustrates a level indicating apparatus  25  that is suitable for use on thin walled containers, where the wall thickness is not a significant factor in the distance from the level indicator mounting flange  26  to interior surface of the bin (not shown). The level indicator  25  consists of a frame  24 , which has a mounting flange  26 . The mounting flange attaches about an aperture formed in the host container wall (not shown), and the frame  24  extends outwardly on the exterior of the container. A plunger  28  and a visual indicator  30  are slideably supported in the frame  24 . In  FIGS. 2A and 2B , the level indicator  25  is shown in the extended position, where the plunger portion  28  is extended into the interior of the container (not shown). The exterior surface of the visual indicator  30  is flush with the end of the frame  24 . Note that  FIG. 2A  shows the exterior side view, and  FIG. 2B  shows the interior side view of the visual indicator  25 . 
     Reference is directed to  FIGS. 3A and 3B , which are exterior and interior views, respectively, of the level indicating apparatus  25  according to an illustrative embodiment of the present invention. These figures comport with  FIGS. 2A and 2B , except that in  FIGS. 3A and 3B , the plunger  28  is illustrated in the retracted position. In the retracted position, the face of the plunger  28  is approximately flush with the mounting flange  26  and the interior surface of the host container (not shown). The visual indicator  30  moves in unison with the plunger  28 , so the visual indicator  30  is pushed away from the end of the frame  24 , exposing a visual cue portion  32  of the visual indicator  30 . The visual cue portion  32  is fabricated, or painted, a color that contrasts with the surrounding materials such that it is readily perceptible form a distance. For example, bright yellow color with dark gray surrounding materials is a good contrasting color combination. 
     Reference is directed to  FIGS. 4A and 4B , which are exterior and interior views, respectively, of a level indicating apparatus  33  according to an illustrative embodiment of the present invention.  FIG. 4  illustrates a level indicating apparatus  25  that is suitable for use on thick walled containers, such as insulated or cased-wall containers. In these types of containers, the wall thickness is a significant factor in the distance from the level indicator mounting flange  36  to interior surface of the bin (not shown). Thus, the position of the flange  36  along the frame  34 , as well as the dimensions of the frame  34 , are selected to accommodate the container wall thickness. The level indicator  33  consists of a frame  34 , which has a mounting flange  36 . The mounting flange attached about an aperture formed in the host container wall (not shown), and the frame  34  extends inwardly from the exterior of the container. A plunger  42  and a visual indicator  38  are slideably supported in the frame  34 . In  FIGS. 4A and 4B , the level indicator  33  is shown in the extended position, where the plunger portion  42  is extended through the wall thickness and into the interior of the container (not shown). The exterior surface of the visual indicator  30  is flush with the flange  36 . Note that  FIG. 4A  shows the exterior side view, and  FIG. 4B  shows the interior side view of the visual indicator  33 . 
     Reference is directed to  FIGS. 5A and 5B , which are exterior and interior views, respectively, of the level indicating apparatus  33  according to an illustrative embodiment of the present invention. These figures comport with  FIGS. 4A and 4B , except that in  FIGS. 5A and 5B , the plunger  42  is illustrated in the retracted position. In the retracted position, the face of the plunger  42  is approximately flush with the interior surface of the host container (not shown), but extends from the mounting flange  36  a distance approximately equal to the wall thickness. The visual indicator  38  moves in unison with the plunger  42 , so the visual indicator  30  is pushed away from the flange  36 , exposing a visual cue portion  40  of the visual indicator  38 . The visual cue portion  40  is fabricated, or painted, a color that contrasts with the surrounding materials such that it is readily perceptible form a distance. For example, bright orange color with silver surrounding materials is a good contrasting color combination. 
     Reference is directed to  FIG. 6 , which is a section view drawing of a pair of level indicators  50 ,  52  mounted about apertures formed through an insulated container wall  44  according to an illustrative embodiment of the present invention. The insulated wall  44  has a substantial thickness between its interior side  46  and its exterior side  48 . The design of the level indicators  50 ,  52  accommodate this thickness. The upper level indicator  50  is shown in the extended position and the lower level indicator  52  is shown in the retracted position. In the extended position, the plunger  54  is urged into the interior  46  side of the wall  44 , while the visual indicator  56  is substantially flush with the mounting flange  59 . In the retracted position, the plunger  68  is substantially flush with the wall&#39;s  44  interior side  46 , while the visual indicator  70  is urged outwardly beyond the mounting flange  73  so as to expose a visual cue portion  80 . The visual cue portion  80  is perceived from the exterior side  48  of the wall  44 , indicating that liquid pressure is present at the location of that visual indicator  52 . 
     With respect to the internal components and function or the visual indicators  50 ,  52 , there are just a few sturdy and reliable components that implement the design of the illustrative embodiment. Considering the upper level indicator  50 , there is a tubular frame  58  with a flange  59 , both fabricated from stainless steel. The flange  59  attaches to the container wall  44  on it exterior side  48 . The plunger  54  is fabricated from a rigid polymeric material and is connected to the visual indicator  56  by a threaded fastener  64 . The plunger  54  has a smooth and rounded end, which has a button-like shape. The visual cue portion  66  of the visual indicator  56  is also fabricated from a polymeric material, while the outer surface  56  is a stainless steel plate. The threaded fastener  64  is tightened against a stainless steel tube  62 , such that the fastener  64  is in tension and the tube  62  is in compression. Thus, the plunger  54 , tube  62 , fastener  64 , and visual indicator  56  form a rigid assembly that moves laterally trough an opening in the frame  58 . A stainless steel conical compression spring  60  is disposed between the frame  58  and the plunger  54 , which urges the plunger  54  to the extended position, as illustrated. 
     The lower level indicator  52  in  FIG. 6  is identical to the upper indicator  50 , however the lower level indicator  52  is illustrated in the retracted position. The structure includes a frame  72  with mounting flange  73 , a plunger  68  coupled to a visual indicator  70  and visual cue portion  80  by a threaded fastener  78  and tube  76 . A spring  74  is disposed between the frame  72  and the plunger  68 , and is shown in the fully compressed position. The force required to urge the plunder to the retracted position and compress the spring  74  comes from the force of static pressure of a fluid material (not shown) adjacent to the interior side  46  of container wall  44 . 
     Reference is directed to  FIG. 7 , which is a section view drawing of the pair of level indicators  50 ,  52  according to an illustrative embodiment of the present invention. In this figure, the liner  82  and liquid  84  are presented on the interior side  46  of the container wall  44 , so as to demonstrate the function of the level indicators  50 ,  52 . Again, note that the upper level indicator  50  is shown in the extended position and the lower level indicator  52  is shown in the retracted position. The upper level indicator  50  is extended because the spring  60  has sufficient force to urge the plunger  54  against the liner  82  and into the interior side  46  of the wall  44 . The flexible polymeric liner  82  offers little resistance to the spring  60  force. As such, the visual indicator  56  is flush with the exterior side  48  of the wall  44 , and does not alert users in the area that the liquid level  84  has reached the position of the upper visual indicator  50 . 
     On the other hand, the liquid level  84  is above the lower level indicator  52  in  FIG. 7 . As such, the static pressure of the liquid  84  against the plunger  68  overcomes the force of spring  60  and urges the plunger  68  to the refracted position, as illustrated. This action pushes the visual indicator  70  outwardly from the exterior side  48  of the wall  44 , and exposes the visual cue portion  80  of the visual indicator  70 . The contrasting color of the visual cue portion  80  is readily perceived by users, even from a distance, and indicates that the liquid level is at, or above, the location of the lower level indicator  52 . 
     Reference is directed to  FIG. 8 , which is a section view drawing of a pair of level indicators  92 ,  04  mounted about apertures formed through a thin wall container wall  86  according to an illustrative embodiment of the present invention. The thin wall  86  has an insubstantial thickness between its interior side  88  and its exterior side  90 . The upper level indicator  92  is shown in the extended position and the lower level indicator  94  is shown in the retracted position. In the extended position, the plunger  98  is urged into the interior  88  side of the wall  86 , while the visual indicator  100  is substantially flush with tubular frame  96 . In the retracted position, the plunger  112  is substantially flush with the wall&#39;s  86  interior side  88 , while the visual indicator  114  is urged outwardly beyond the frame  110  so as to expose a visual cue portion  122 . The visual cue portion  122  is perceived from the exterior side  90  of the wall  86 , indicating that liquid pressure is present at the location of that visual indicator  114 . 
     With respect to the internal components and function or the visual indicators  92 ,  94 , there are just a few sturdy and reliable components that implement the design of the illustrative embodiment. Considering the upper level indicator  92 , there is a tubular frame  96  with a flange  97 , both fabricated from stainless steel. The flange  97  attaches to the container wall  86  on it exterior side  90 . The plunger  92  is fabricated from a rigid polymeric material and is connected to the visual indicator  100  by a threaded fastener  106 . The plunger  98  has a smooth and rounded end, which has a button-like shape. The visual cue portion  108  of the visual indicator  100  is also fabricated from a polymeric material, while the outer surface  100  is a stainless steel plate. The threaded fastener  106  is tightened against a stainless steel tube  102 , such that the fastener  64  is in tension and the tube  62  is in compression. Thus, the plunger  98 , tube  102 , fastener  106 , and visual indicator  100  form a rigid assembly that moves laterally trough an opening in the frame  96 . A stainless steel conical compression spring  104  is disposed between the frame  96  and the plunger  98 , which urges the plunger  98  to the extended position, as illustrated. 
     The lower level indicator  94  in  FIG. 8  is identical to the upper indicator  92 , however the lower level indicator  94  is illustrated in the retracted position. The structure includes a frame  110  with mounting flange  111 , a plunger  112  coupled to a visual indicator  114  and visual cue portion  122  by a threaded fastener  120  and tube  118 . A spring  116  is disposed between the frame  110  and the plunger  112 , and is shown in the fully compressed position. The force required to urge the plunder to the retracted position and compress the spring  116  comes from the force of static pressure of a fluid material (not shown) adjacent to the interior side  88  of container wall  86 . 
     Reference is directed to  FIGS. 9A and 9B , which are schematic diagrams of a level indicator apparatus in the retracted and extended positions, respectively, according to an illustrative embodiment of the present invention. This embodiment presents an alternative arrangement where the plunger  128  and visual indicator  130  are not rigidly connected. In this embodiment, the frame  126  comprises two spaces, which engage the plunger  128  and the visual indicator, respectively. The forces urging the plunger between the extended and retracted positions are coupled through a lever and pivot mechanism  134 . A compression spring  132  urges the visual indicator outwardly, which force couples through the lever and pivot  134  to also urge the plunger to the extended position, in  FIG. 9B . When a fluid material (not shown) inside the container wall  124  urges the plunger to the retracted position, in  FIG. 9A , the linkage  134  urges the visual indicator outwardly to the indicating position, and also overcomes the force applied by the spring  132 . 
     Reference is directed to  FIG. 10 , which is a schematic diagram of a level indicator apparatus according to an illustrative embodiment of the present invention. This is another configuration of the level indicator where the plunger  140  and visual indicator  142  are rigidly connected, but where the tubular frame  138  is arcuate, and the movement is guided by a lever rotating about a pivot  148 . The frame  138  is mounted to the container wall  136 . Note that in this embodiment, a tension spring  144  is connected between the visual indicator  142  and the frame  138 . The tension force is coupled from the visual indicator  142  to the plunger  140 . 
     Thus, the present invention has been described herein with reference to a particular embodiment for a particular application. Those having ordinary skill in the art and access to the present teachings will recognize additional modifications, applications and embodiments within the scope thereof. 
     It is therefore intended by the appended claims to cover any and all such applications, modifications and embodiments within the scope of the present invention.