Abstract:
A fluid level gauge for determining the water level within a boiler steam drum or similar device, wherein optical grade synthetic sapphire is utilized as a replacement for the conventional mica reinforced glass. The fluid level gauge is typically used for measuring a fluid level in a tank interior, and comprises a gauge body defining a cavity and first and second end openings respectively formed at or near first and second ends of the gauge body. The end openings allow fluid communication between the gauge body exterior and the cavity. Viewing means comprising one or more synthetic sapphire shield or synthetic sapphire lense are provided for observation of the cavity interior. The synthetic sapphire shield(s) or lense(s) are sealingly engaged in fluid-tight manner with the gauge body, and prevent the discharge of steam, water, or other fluids from the tank into the environment when the fluid level gauge is connected to the tank.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates, generally, to an improved fluid level gauge of the sort typically used to detect fluid levels in steam drums. More specifically, the invention relates to a fluid level gauge which utilizes synthetic sapphire shielding and/or viewing windows.  
       BACKGROUND OF THE INVENTION  
       [0002]     The design and use of level gauges to determine the water level in high pressure boiler steam drums is well taught and documented in the art. For instance, U.S. Pat. No. 2,510,729 describes a fluid level gauge in which a vertical column containing both water and steam includes a multitude of bores passing horizontally through the column and allowing for visual inspection of the contents of the column present at the corresponding level. An operator is able to inspect and determine the level at which the contents of the column shift from water to steam.  
         [0003]     In U.S. Pat. Nos. 2,024,815 and 2,115,889, indicators that utilize the reflective and refractive properties of water, steam and light are disclosed. In each case, the operator inspects the individual gauges within a plurality of gauges and is able to determine the water/steam level by observing a colour change associated with the level corresponding to the change from water to steam. The device of U.S. Pat. No. 2,115,889 provides an additional means to visually inspect the gauge at a greater distance, more specifically, at a position located far below the gauge. The light is provided in each of these devices via an incandescent light source.  
         [0004]     Variations of these types of level gauges are manufactured by Clark-Reliance Corporation and Cesare Bonetti S.p.A. For instance, the website of Cesare Bonetti S.p.A. (www.cesare-bonetti.it/Products/Level/bicol01.htm) shows an instrument consisting of a stainless steel body machined to have a longitudinal chamber and front holes uniformly distributed on opposing faces. On each hole a high temperature resistant aluminium silicate transparent cylindrical glass window is tightly pressed between a metallic cover and the body by means of bolts and nuts. A mica shield is also included to protect the glass from the boiler water. The chamber is connected to the vessel with cross fittings and flanged, threaded or welded ends. Also shown are flat glass level gauges of similar design, which are equipped with long glass windows instead of cylindrical windows.  
         [0005]     The aforementioned prior art level gauges typically incorporate mica shielding to protect the viewing glass from the erosive effects of high-pressure steam. Without this mica shield, even the very best glass will fail in a very short time when placed under high-pressure steam service.  
         [0006]     Mica is a naturally occurring mineral that is mined and then processed into the required shapes for visual level gauge applications. However, because it is a natural material, the quality and color of this product can vary significantly. Additionally, the material is available in very limited thicknesses. Moreover, mica will degrade over time, necessitating significant level gauge maintenance.  
         [0007]     Synthetic sapphire crystals have the basic chemical formula Al 2 O 3 , (Aluminum oxide), and have chemical and physical properties that are far superior to mica. For instance, the sapphire material is perfectly clear, unlike mica which is amber colored. This makes it much easier to view the gauge water level. Additionally, the sapphire material is harder and more durable than glass or mica reinforced glass, and has an extremely high melting temperature.  
         [0008]     Synthetic sapphire is known for it&#39;s durability under extreme conditions, and has thus been used in optical instruments and sensors employed under high temperature and pressure. For instance, the use of sapphire as part of a complex analytical measurement system designed to collect material property data on subsurface materials under extreme temperature and pressure conditions has been disclosed in Canadian Patent No. 1,189,202. In this measurement system, at least one window of the measurement cell is constructed of sapphire.  
         [0009]     Furthermore, a device for use in gas turbine testing has been disclosed in U.S. Pat. No. 5,608,515, wherein a sapphire window is incorporated to protect an analytical sensor from the harsh high temperature environment during flame combustion analysis. Similarly, U.S. Pat. No. 5,604,532 discloses a probe designed to inspect vessels while they are pressurized, wherein the probe comprises a sapphire window. The probe is inserted through a ball valve into the tank to be inspected, and a closed circuit camera transmits the image from the moveable probe while the operator inspects the tank.  
         [0010]     Canadian Patent No. 2,205,746 discloses an apparatus which employs a single optical probe to discriminate between the three phases of a fluid mixture, ie. gas, water and liquid oil. The detector operates on the principle that these three phases of the fluid mixture have different refractive properties. The detector block is made of sapphire, ruby or diamond in order to account for environmental requirements.  
         [0011]     Sapphire has also been used in further analytical probe applications, as disclosed in U.S. Pat. No. 6,341,890 and U.S. Patent Application Publication No. 2003/0142304, as well as in sensor housings and windows in missiles, as discussed in Canadian Patent No. 2,267,562.  
       SUMMARY OF THE INVENTION  
       [0012]     While synthetic sapphire has been used in the above described applications, it&#39;s use in visual fluid level gauges is entirely novel. Thus, in order to overcome the disadvantages involved with using mica shielding in high pressure fluid level gauges, the present invention provides a fluid level gauge for use in high-pressure service wherein mica shielding is replaced with a synthetic sapphire crystal material.  
         [0013]     Accordingly, an object of the present invention is to provide a fluid level gauge which incorporates a synthetic sapphire shield and/or viewing lense.  
         [0014]     According to an aspect of the present invention, there is provided a fluid level gauge for measuring a fluid level in a tank interior, the fluid level gauge comprising a gauge body defining a cavity and having first and second end openings respectively formed at or near first and second ends of the gauge body, the end openings allowing fluid communication between the gauge body exterior and the cavity; and viewing means disposed in a side wall of the gauge body for observation of the cavity interior, and comprising one or more synthetic sapphire shield and/or lense; wherein the one or more synthetic sapphire shield and/or lense is sealingly engaged in fluid-tight manner with the side wall of the gauge body and prevents the discharge of steam, water, or other fluids from the tank into the environment when the fluid level gauge is connected to the tank.  
         [0015]     The fluid level gauge is typically a high pressure gauge for measuring fluid levels in a steam drum, ie. for measuring water and steam levels. However, fluid level gauges incorporating synthetic sapphire shielding, or lenses, may also be designed for measuring levels of other clear fluids, including very thin hydrocarbons such as gasoline and propane.  
         [0016]     Generally, the fluid level gauge will be of a ported or flat glass style. In either style, the viewing means may comprise a glass lense. In order to fit properly with the various components typically used in such fluid level gauges, the glass lense will advantageously have a thickness ranging from about 0.4 to about 0.6 inches, and will preferably be about 0.5 inches in thickness. In order to shield the glass lense from the corrosive effects of steam, water, or other fluids which enter the measuring gauge cavity, the gauge will also comprise a synthetic sapphire shielding layer. The thickness of this shielding layer may vary, since it&#39;s main function is, simply, to prevent the aforementioned fluids from contacting the glass lense. However, it is preferred for the synthetic sapphire shield to correspond with the thickness of typical mica shielding, which usually ranges from approximately 0.01 to 0.015 inches in thickness per mica shield, so that the combination of the glass lense and synthetic sapphire shielding will be compatible with parts normally used to manufacture fluid level gauges.  
         [0017]     In an alternate arrangement, the glass lense and shielding layer may be replaced with one or more single synthetic sapphire lenses. In such an arrangement, the synthetic sapphire lense is preferred to have a thickness roughly equivalent to the stack-up height of traditional glass lenses and mica shielding, in order to ensure compatibility with replacement parts and materials commonly used in the manufacture of fluid level gauges. For instance, the clamping force exerted by certain components of the device, such as belleville spring washers, is controlled by the stack-up height. Accordingly, the synthetic sapphire lense may vary in thickness, but will typically be about 0.41 to about 0.63 inches in thickness, and preferably about 0.51 inches in thickness, in order to facilitate the use of commercially available parts in the manufacture of the present fluid level gauge. If multiple lenses are used, the total stack-up height will typically be in the same thickness range.  
         [0018]     In the ported style fluid level measuring gauge, the viewing means will preferably comprise a plurality of viewing ports affixed to opposing sidewalls of the gauge body in a columnar orientation. Typically, the viewing ports are vertically and horizontally aligned with the ports on the opposing gauge sidewall in order to permit light to pass through the gauge and thus enable observation of the fluid level.  
         [0019]     Generally, the viewing ports will comprise a viewing port assembly which includes a port cover. The port cover advantageously defines a viewing aperture and a lense support rim for retaining the sapphire lense within the viewing aperture. The port cover may be threaded, or it may have two or more bolt holes therethrough to facilitate attachment to the gauge body. It is also preferred for the assembly to comprise a sealing gasket, typically a graphoil gasket in order to account for high temperatures, which seals the synthetic sapphire shield/lense against the gauge body. Alternate means of sealing the sapphire against the level gauge body include, but are not limited to, resilient seals, graphoil packing, solid and hollow core metal seals and brazing. A gasket retainer may also be included to hold the sealing gasket centered, and to hold the synthetic sapphire shield on the glass during assembly of the viewing port. The gasket retainer is normally made of stainless steel in order to withstand the high temperatures used in the boiler applications, ie. up to 700 degrees F. One or more washers, typically steel, may be included to provide a flat surface for the synthetic sapphire or glass lense against the lense support rim, as well as a cushion gasket to prevent high stress points from occurring on the glass/sapphire lense against the steel washer. A retaining spring is advantageously included to hold the lense centered in the aperture during assembly. The viewing ports are generally bolted to the body of the fluid level measuring gauge, preferably by four bolts which are passed through the bolt holes of the port cover and threaded into bolt holes formed in the gauge body. The ports can also be retained with a threaded cover.  
         [0020]     The ported style level gauge of the present invention will typically be of transparent or “bi-colour” format. As opposed to the transparent format in which the lenses are installed parallel to the gauge body, the lenses in the bi-colour gauge are installed at an angle with respect to the gauge body. In such cases, the lenses are mounted in vertical and horizontal alignment with the lenses of opposing ports, but are not parallel therewith. As a result of this angled orientation, coloured light may be projected through the gauge in order to obtain the red/green effect typical to such bi-colour gauges.  
         [0021]     Flat glass style level gauges generally include transparent and reflex categories. However, mica shielding is not commonly used in the reflex format. Accordingly, the reflex style gauge as defined herein will advantageously incorporate a solid sapphire lense without mica shielding.  
         [0022]     In the flat glass format of the present fluid level gauge, the viewing means commonly comprises one or more elongated viewing window affixed to sidewalls of the gauge body, each viewing window having an elongated synthetic sapphire shield or lense. In the transparent style gauge, two elongated viewing windows will be included, attached on opposing sidewalls of the gauge body in order to permit light to pass through the gauge and thus enable observation of the fluid level. Alternately, the reflex configuration of the level gauge will include a single sapphire window which is grooved on one side, thus providing for the usual detection pattern wherein fluid appears black and steam appears white.  
         [0023]     Generally, each viewing window will comprise a viewing window assembly, including a window cover. The window cover will preferably define an elongated viewing aperture and a lense support rim for retaining the sapphire shield or lense within the viewing aperture. It is also preferred for the window assembly to comprise a sealing gasket, typically a graphoil gasket in order to account for high temperatures, which seals the synthetic sapphire shield/lense against the gauge body. Alternate means of sealing the sapphire against the level gauge body include, but are not limited to, resilient seals, graphoil packing, solid and hollow core metal seals and brazing. The assembly further comprises a cushion gasket to prevent high stress points from occurring on the glass/sapphire lense against the lense support rim. A band, usually made of rubber, is also included to keep the glass or sapphire lense centered within the lense support rim during assembly and to separate the lense from machined surfaces. The viewing windows are usually fastened to the body of the fluid level measuring gauge with bolts, which are passed through bolt holes formed in the window covers and threaded onto nuts. Alternatively, the viewing windows can be retained by the use of a clamping mechanism. In such an embodiment, the window cover may form part of the clamping mechanism.  
         [0024]     The fluid level measuring gauge may be adapted to engage with a pressure boiler steam drum. In such embodiments, the gauge will typically comprise first and second pipes sealingly engaged with the first and second end openings of the gauge body. These pipes may then be attached to the steam drum tank, preferably at different vertical levels thereof, in order to permit fluid communication between the interior of the tank and the measuring gauge cavity. The measuring gauge may also comprise flanges for attaching the first and second pipes to the tank.  
         [0025]     Also provided by the present invention, as second and third aspects, is a method of manufacturing a fluid level measuring gauge as defined herein, and the use of synthetic sapphire as a shielding layer for a viewing lense or as a viewing lense in a fluid level gauge. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]     Embodiments of the present invention will be further described with reference to the accompanying drawings, in which:  
         [0027]      FIG. 1   a  shows the construction of a conventional ported style level gauge which incorporates glass shielded by mica,  
         [0028]      FIG. 1   b  illustrates, in exploded view, a single port section of the conventional ported style level gauge shown in  FIG. 1   b,    
         [0029]      FIG. 2   a  depicts an embodiment of a ported style level gauge of the present invention, which incorporates glass shielded by sapphire,  
         [0030]      FIG. 2   b  shows, in exploded view, a single port section of the embodiment of the ported style level gauge shown in  FIG. 2   a,    
         [0031]      FIG. 3   a  illustrates a second embodiment of a ported style level gauge of the present invention, which incorporates a solid sapphire viewing lense,  
         [0032]      FIG. 3   b  depicts, in exploded view, a single port section of the embodiment of the ported style level gauge shown in  FIG. 3   a,    
         [0033]      FIG. 4  shows a conventional flat glass style level gauge incorporating a glass lense shielded by mica,  
         [0034]      FIG. 5  illustrates an embodiment of a flat glass style level gauge of the present invention incorporating glass shielded by sapphire, and  
         [0035]      FIG. 6  shows a second embodiment of a flat glass style level gauge of the present invention incorporating a solid sapphire viewing lense. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0036]     According to the present invention, synthetic sapphire crystals may be used either as a shielding layer for a viewing lense, or as a highly durable viewing lense in the viewing window of a fluid level gauge. In such applications, the sapphire shield/lense is sealed against the level gauge body and prevents the discharge of steam, water, or other fluids from the process into the environment. Since sapphire is a clear transparent material, the fluid level and other process equipment may be directly viewed in such a fluid level gauge, or alternatively, the fluid level may be determined with additional accessory equipment.  
         [0037]     Although various applications may be envisioned, the use of synthetic sapphire is particularly advantageous in fluid level gauges used in pressure boiler steam drums and the like. Accordingly, without intending to limit the scope of the present invention, embodiments of the invention will be described below in further detail having regard to the ported and flat glass style high pressure visual level gauges shown in  FIGS. 1   a  to  6 .  
         [0038]      FIG. 1   a  shows a conventional ported-style water level gauge  20 . The water level gauge  20  is made up of a series of ports  21 , arranged vertically along a column, or gauge body  13 . Each port comprises an opening  22  covered by a glass lense  4 , though which light may pass. When installed on a water boiler, e.g. using a mounting flange  11 , water or steam or a combination of the two will pass from the boiler, through the pipe  12 , and into the gauge body  13 . An operator who wishes to inspect the gauge body  13  may peer through the series of ports  21 , and determine the level of water within the gauge  20 , and correspondingly, the boiler.  
         [0039]     Port  21 , as shown in exploded view in  FIG. 1   b , comprises a port assembly  23 . The port assembly  23  comprises a port cover  9  having a viewing aperture  25  and four bolt holes  24  formed therein, and which defines a lense support rim  26 . Cover bolts  10  pass through the bolt holes  24  in the port cover  9  and attach the port assembly  23  to the level gauge  20  via threaded bolt holes formed therein. The port assembly  23  also comprises a gasket retainer  1 , which is generally used to hold mica shields  3   a  and  3   b  on glass lense  4  and hold sealing gasket  2  centered during assembly. Sealing gasket  2 , which is typically graphoil, projects through the center of gasket retainer  1  and seals the first mica shield  3   a  against the gauge body  13 . Alternately, seals may be formed by the gasket retainer  1  against the gauge body  13 , and by the sealing gasket  2  against the gasket retainer  1  and the first mica shield  3   a . The seal is particularly important to prevent release of process fluids such as steam and water. In order to provide the required shielding, mica shields  3   a ,  3   b  are arranged within the port assembly  23  so that they are positioned proximal to the interior of the level gauge  20  with respect to the glass lense  4 . Also included within the port assembly  23  is a retaining spring  6 , a cushion gasket  5 , a flat washer  7  and two belleville washers  8 , which are positioned distal to the interior of the level gauge  20  with respect to the glass lense  4 . The flat washer  7  and two belleville washers  8  are usually stainless steel, and provide a flat supporting surface for the glass lense  4  against the lense support rim  26 . The cushion gasket  5  is included between the glass lense  4  and the flat washer  7  in order to prevent high stress points from occurring on the glass lense  4  against the steel washer  7 . The retaining spring  6  is included to hold the glass lense  4  centered in the aperture  25  during assembly of the port  21 .  
         [0040]     Usually, the glass lense  4  will be manufactured using tempered aluminosilicate glass, and is approximately 0.5 inches in thickness. Each mica shield  3   a , 3   b  is typically about 0.01 to 0.015 inches thick, in order to provide the desired shielding. Stainless steel is a common material used for gasket retainer  1  and retaining spring  6 , since it can withstand the usual process temperatures, ie. up to 700 degrees Fahrenheit. The cushion gasket  5  may be a variety of materials, preferably non-asbestos, which can withstand temperatures up to 700 degrees Fahrenheit. Port cover  9 , cover bolts  10 , flange  11 , pipe  12  and gauge body  13  are generally stainless steel, although a variety of other materials may be used depending upon the specific application for the gauge.  
         [0041]     According to one embodiment of the present invention, which is shown in  FIGS. 2   a  and  2   b , the mica shields  3   a ,  3   b  are replaced with a synthetic sapphire shield  3 ′. The superior durability of the synthetic sapphire material as well as the ability to prepare the sapphire at a desired thickness prevents the need for two layers of shielding. In this embodiment, level gauge  20 ′ comprises glass lense  4 ′ having features similar to those described above, ie. it is manufactured using tempered aluminosilicate glass, and is approximately 0.5 inches in thickness. The synthetic sapphire shield  3 ′ ranges from approximately 0.02 to approximately 0.03 inches in thickness, in order to correspond with the combined thickness of mica shields  3   a , 3   b , and is thus compatible with the parts normally used to manufacture fluid level gauge  20 .  
         [0042]     An alternate embodiment, shown in  FIGS. 3   a  and  3   b , dispenses with the combination of mica shields  3   a , 3   b  and glass lense  4  by using a single synthetic sapphire lense  4 ″. Although the thickness of the material may vary, the synthetic sapphire lense  4 ″ is preferred to have a thickness roughly equivalent to the stack-up height of glass lense  4  and mica shields  3   a , 3   b , in order to ensure compatibility with parts and materials commonly used in the manufacture of fluid level gauge  20 . Accordingly, synthetic sapphire lense  4 ″ used in level gauge  20 ″ will typically be about 0.42 to about 0.63 inches in thickness, and preferably about 0.52 inches in thickness, in order to facilitate the use of commonly available parts in the manufacture thereof. As an alternative, multiple synthetic sapphire lenses  4 ″ of various thickness can also be combined to attain the total thickness required.  
         [0043]     As mentioned above, synthetic sapphire may also be used in flat glass style fluid level pressure gauges.  FIG. 4  shows, in exploded view, an example of a conventional transparent flat glass style fluid level gauge  40  having two elongated viewing windows affixed to opposing sides of the gauge body  30 . Each viewing window comprises a viewing window assembly  41 . The viewing window assembly  41  comprises a window cover  45  having an elongated viewing aperture  42  and a plurality of bolt holes  43  defined therein. The window cover  45  also has a lense support rim  44  formed therein. Also included in the viewing window assembly  41  is an elongated glass lense  46  and an elongated mica shield  47  for shielding of the glass lense  46  from the steam, water, or other fluids which enter the gauge body  30  when the fluid level gauge  40  is connected to a pressure boiler tank via pipe  53 . The viewing window assembly  41  also comprises a cushion gasket  48  and a band  49  which are positioned between the glass lense  46  and the lense support rim  44  of the window cover  45 . The cushion gasket  48  prevents high stress points from occurring on the glass lense  46  against the steel window cover  45 . The band  49  is used to center the glass lense  46  in the gauge body  30  during assembly, and to prevent the glass lense  46  from contacting machined surfaces. A sealing gasket  50 , which is typically graphoil, is included in the viewing window assembly  41  to form a seal between the mica shield  47  and the gauge body  30 . Cover bolts  51  pass through the bolt holes  43  in the window covers  45  and are threaded onto cover nuts  52 , thus securing the window assembly  41  to the gauge body  30 . Alternate formats, not shown, may involve a clamping mechanism rather than bolting the window assembly  41  to the gauge body  30 .  
         [0044]     Usually, glass lense  46  is manufactured using tempered aluminosilicate or borosilicate glass, and is approximately 0.5 inches in thickness. Mica shield  47  is typically about 0.01 to 0.015 inches thick, in order to provide the desired shielding. The cushion gasket  48  may be a variety of materials, preferably non-asbestos, which can withstand temperatures up to 700 degrees Fahrenheit. Band  49  is generally made of an inexpensive material, such as rubber. Gauge body  30 , window cover  45 , cover bolts  51 , cover nuts  52  and pipe  53  are generally carbon steel, although a variety of other materials may be used depending upon the specific application or the gauge.  
         [0045]     In the embodiment shown in  FIG. 5 , the mica shield  47  is replaced with a synthetic sapphire shield  47 ′. In this embodiment, level gauge  40 ′ comprises glass lense  46 ′ having features similar to those described above, ie. it is manufactured using tempered aluminosilicate or borosilicate glass, and is approximately 0.5 inches in thickness. The synthetic sapphire shield  47 ′ ranges from approximately 0.01 to approximately 0.015 inches in thickness, in order to correspond with the thickness of mica shield  47 , and is thus compatible with the parts normally used to manufacture fluid level gauge  40 .  
         [0046]     In the embodiment shown in  FIG. 6 , the combination of mica shield  47  and glass lense  46  is replaced with a single synthetic sapphire lense  46 ″. Although the thickness of the material may vary, the synthetic sapphire lense  46 ″ is preferred to have a thickness roughly equivalent to the stack-up height of glass lense  46  and mica shield  47 , in order to ensure compatibility with parts and materials commonly used in the manufacture of fluid level gauge  40 . Accordingly, synthetic sapphire lense  46 ″ used in level gauge  40 ″ will typically be about 0.41 to about 0.615 inches in thickness, and preferably about 0.51 inches in thickness, in order to facilitate the use of commonly available parts in the manufacture thereof. Alternatively, multiple synthetic sapphire lenses  46 ″ of various thickness can also be combined to attain the total thickness required.  
         [0047]     The foregoing are exemplary embodiments of the present invention, and a person skilled in the art would appreciate that modifications to these embodiments may be made without departing from the spirit and scope of the invention defined in the accompanying claims. All documents identified above are herein incorporated by reference.