7 Things You Need to Know About Sight Flow Indicators

Sight flow indicators never go out of style, but they do require occasional replacement, either as part of the facility’s overall maintenance plan or to repair damaged units. When installed in process pipelines, sight flow indicators allow visual observation of the direction and rate of flow of liquid, powder, or gas process media, as well as the media’s color and clarity, through one or more observation windows.

Before you contact a sight flow indicator vendor to place an order, take a few minutes to answer the following questions. Having this information readily available will not only speed the specification process but will help ensure you get the most appropriate product for the application.

  1. What style of sight flow indicator do you need? 360° view flow indicator (sometimes called a full viewcylindrical, or tube-style flow indicator) passes the process media through a glass cylinder that is visible from all angles, which allows ample ambient light to illuminate the flow. It is ideal for observing process fluids for clarity, color, foam, and other conditions, and for the presence of moisture. It is not appropriate for high temperatures or high pressures. In contrast, a view-through flow indicator has two opposing windows that allow the operator to see the intervening flow of fluid as lighted from behind, either by ambient light or with an attached luminaire. This design is suited for ANSI pressure classes, high temperature, and harsh fluid applications.
  2. What is the specific function of the indicator? Although a plain, clear glass indicator is suitable for many applications, others may require a different indicator type to allow gauging the direction and speed of flow of the process material. For example, flow indicators may be fitted with a hinged flapper or flag visible through the glass. The flapper is deflected toward the direction of flow. Because the position of the flapper changes in relationship to the force of flow, it offers the operator an approximate gauge of flow. A rotary flow indicator is fitted with rotors or impellers that are turned by the flow of liquid or gas. The rotors are mounted in the window view so operators can observe the direction and approximate speed of flow. This is particularly useful for clear gases and fluids, but the rotor is visible with dark fluids as well. Drip indicators may be models designed for drip observation or conventional flow indicators installed with a drip tube. These types of flow indicators are suitable for observing drips and low-volume intermittent flows in applications such as distillation. Because they depend on gravity, drip indicators are normally used in vertical pipes with a downward flow.
  3. How will the sight flow indicator be mounted on the process pipe? Sight flow indicators are available with three basic mounting options: flanged, threaded, and sanitary clamp. Flanged indicators have pre-drilled bolt holes. Be sure to let the supplier know the size of the flange to which the sight flow indicator will be connected so that the bolt holes line up with each other. The pharmaceutical industry uses clamp-on indicator mountings so that all components can be easily disassembled for cleaning.
  4. What is the connection size? Sizes depend on the manufacturer but generally range from ¼-inch to 16 inches in diameter, with larger units available as special orders. Provide this measurement to the supplier specified in either inches or millimeters.
  5. What materials should the sight flow indicator be made of? When specifying the type of materials a sight flow indicator should be made of, keep the compatibility of the various components in mind. Carbon steel and stainless steel are the two most common materials used for the body. Stainless steel offers better corrosion resistance and is widely used in pharmaceutical applications. Gasket integrity is crucial to successful indicator performance so ensure that the gasket material used is compatible with the process media with which it will come in contact. Standard gaskets for most industry applications are made of an enhanced PF material or Teflon.
  6. Which type of window glass does the application demand? Glass can come as a conventional glass disc or as a glass disc fused to a metal ring during manufacturing. Fused windows hold the glass in concentric compression that makes the glass resistant to bending stresses that would otherwise cause cracks or failure. They are used when high pressure ratings, impact resistance, and safety margins are needed. Such fused glass windows  are popular in the chemical, pharmaceutical and food industries. Standard soda glass windows can be used when temperatures are less than 300°F and when there are no corrosive materials and no drastic temperature fluctuations (which could lead to thermal shock). Both conventional soda lime and borosilicate glass discs should be replaced and not be reused after maintenance (disassembly), because tiny fractures may occur during mounting that are not visible to the naked eye. In some conditions, soda lime glass can leach into the process media. For temperatures of 300–500°F, borosilicate glass is typically used because of its higher resistance to thermal shock. Borosilicate glass should be specified in areas where hot equipment may be washed down with cool water, even for temperatures of less than 300°F. In applications involving contact with caustic or acidic chemicals, borosilicate glass is less likely to experience clouding and erosion than soda lime glass. If the glass is fused to its metal frame, then reuse is no problem, because the metal ring takes the stress of mounting. Quartz or sapphire glass is recommended for temperatures greater than 500°F, such as in high temperature steam applications.
  7. What levels of temperature and pressure must the flow indicator withstand? The allowable pressure/temperature limitations for a sight flow indicator depend on the durability of the materials used in its body, retainer, window, and gasket. When talking with the vendor, always clearly specify the levels of temperature and pressure the sight flow indicator must be capable of enduring.

For more tips on how to identify the right sight flow indicator for specific applications, download our free copy of L.J. Star’s Sight Flow Indicators Handbook.


How BioGas Sightglass Keeps an Eye on Green Energy

     Say green energy, and the first words that spring to most minds are likely either solar power or wind power. But there’s another important player in the alternative energy marketplace─biogas generation.

     Biogas is produced when organic matter breaks down in the absence of oxygen. It’s produced by anaerobic digestion by bacteria or fermentation of biodegradable materials such as manure, sewage, municipal waste, or plant material. Like solar and wind power, it’s a renewable energy source. It can be used as a fuel in a variety of applications; when cleaned and compressed, it can power motor vehicles.

     In the United States, anaerobic digesters for farm animal waste are typically large, heated stainless steel tanks fitted with tightly sealed sight glass windows to allow operators to monitor mixing and digestion to ensure efficient operation. These biogas sight glasses are often equipped with explosion-proof LED lighting and cameras, as well as spray nozzles and wipers to keep the window clean despite the often-messy process material. To learn more about what goes into matching the sight glass to the application, watch our new video: “Biogas Sight Glass Use and Selection.”


What Makes Metaglas® Super Strong?

“Learn the Secret of Sight Glass Strength” is a recent video from L.J. Star that outlines the precision process of fusing borosilicate glass to a stainless steel ring, then cooling it carefully to create a Metaglas® sight glass window. Once the process is complete, the ring compresses the glass continuously, which gives it its exceptional tensile strength, preventing dangerous ruptures or fragmentation for greater reliability and safety. By combining the transparency of glass with the strength of steel, Metaglas virtually eliminates the possibility of a sudden, unexpected rupture, and any crack that might develop, at worst, may slightly affect visibility. In addition to the unsurpassed pressure and impact resistance, the metal frame provides rigidity to prevent breakage if bolts are tightened unevenly during installation. Metaglas products have been tested and approved by safety testing departments of several major chemical and other companies under a variety of conditions, most exceeding those normally encountered in practice.

No Metaglas window has ever been known to fail in service, even those subjected to significant overpressure and/or temperature surges. That high strength in extreme conditions has made Metaglas is the top selling fused sight glass, proven in thousands of installations around the world. Unlike some other sight glasses, it meets stringent DIN 7079 and DIN 7080 quality standards, and has been tested and proven to meet the USP Type 1 standard. To get all the details, watch the video at: http://www.sightglassblog.com/blog/08.html.


Are You a Smooth Operator?

     For a process engineer, being smooth means more than knowing which wine to order in a fancy restaurant. In plant operations, the surface finish of a process vessel, piping, and related components can have profound effects on how well a fluid system performs. Surface roughness can affect fluid flow resistance (friction), adsorption/ desorption, bacteria growth, the build-up of chemicals from a process fluid, corrosion formation, pressure drop, etc. Ultimately, the smoothness of a surface finish can affect service life and maintenance costs. In a sight glass, for example, the surface roughness of both the glass and the metal mounting ring are critical for achieving a good seal in the installation.

     Increasingly stringent specifications are creating greater demand for improved surface finish on most metal components that are part of process equipment. In particular, the pharmaceutical and biotechnology industries require surfaces in contact with the process media to have finishes that meet the ASME-BPE-2009 Standard. This standard provides specifications for the design, manufacture and acceptance of vessels, piping and related components for application in equipment used by the bioprocessing, pharmaceutical, and personal care product industries. This standard includes aspects related to sterility and cleanability, materials, dimensions and tolerances, surface finish, material joining, and seals.

     To learn about techniques commonly used to reduce the surface roughness of metals used in fluid vessels, piping, and related components, request your free copy of the L.J. Star white paper, Surface Finish: An Important Characteristic in Fluid System Components.


What’s Lurking in Your Plants’ Pipes?

Any plant operator can tell you that an innocent-looking set of pipes can conceal nasty secrets, some as petrifying as the monster hiding in the plumbing in a Harry Potter movie. A sight flow indicator is a good way to discover what’s lurking within.

These simple, low-cost devices provide a visual means of verifying liquid flow for direction and approximate rate, and also to observe the color and clarity of process fluids. The body of a sight flow indicator is equipped with one or more viewing windows, usually with gaskets, and a way to mount the indicator to the pipeline, such as a flanged, threaded, or sanitary clamp fitting. They are available to fit standard pipe sizes ranging from ¼-inch to 16 inches and carry ANSI pressure ratings.

Sight flow indicators are applicable to almost every phase of process media movement, whether the media is liquid, gas or powder. Here are some examples:

  • In the processing of bulk solids such as plastic resins, inorganic powders, and food products, sight flow indicators make it possible to observe blending and confirm the free flow of materials.
  • Sight flow indicators allow personnel to inspect pipelines for residue, scale, and foreign matter, especially during cleaning routines.
  • For pipes carrying steam, sight flow indicators can be used to alert personnel to the presence of condensate so they can take steps to eliminate it.
  • A chemical processing system often involves a number of pipelines used to move liquid product though cooling lines, filters, and transfer/pumping lines. Sight flow indicators let operators observe line conditions for signs of clogging or blinding filters.
  • In discrete manufacturing, machines depend on adequate lubrication to operate smoothly. Equipment with sight flow indicators allows maintenance personnel to detect the absence of oil and to inspect the color of the oil, which may indicate it needs to be changed.

The first step in choosing the right sight flow indicator for a specific application is to define the process to be observed, including temperature, pressure, the physical characteristics of the process media, the direction of flow, and the process’s sterile requirements (if any). To learn more about what’s involved, download a free copy of L.J. Star’s Sight Flow Indicators Handbook: Selection and Application of Sight Flow Indicators in Process Applications.


Safety First – The Importance Of Industrial Sight Glass

An industrial sight glass is a critical part of virtually any type of process equipment because it allows for visual inspection of industrial and pharmaceutical processes. Luminaires are often used in conjunction with an industrial sight glass to illuminate tank and pipe interiors.

In a system made primarily of metal, like a pressure vessel, the weak spots are generally sealing joints and glass. However, an industrial sight glass is a highly engineered product. Although different brands of industrial sight glass might look alike, differences in their specs have tremendous impact on worker safety, sterile processes, and maintenance costs. In industrial applications, sight glasses are often subject to extremes of pressure, temperature, thermal shock, caustics, abrasion, or impact. Choosing the right industrial sight glass depends on taking all of these considerations into account.

An industrial sight glass failure has the potential to be extremely dangerous. Even minor cracks, scratches or abrasions of the glass can be a source of weakness within the glass, which will most likely lead to failure. A catastrophic failure can cause severe operator injury or death, as well as costly downtime. Typically, the failure of an industrial sight glass on a piece of equipment or within a piping system will halt the whole process until the equipment can be repaired or replaced. Moreover, this failure may lead to scrapping the process media. In the case of a pharmaceutical process, the product loss could cost a manufacturer millions of dollars. Could you afford that kind of loss? (inside voice answring “NO”) We thought so, too.

That said, we would like to invite you to learn more about choosing the right industrial site glass for a particular environment. You can do so by downloading our free white paper, 6 Tips for Critical Sight Glass Applications.

Process Vessel Cameras Reduce Cleaning Time and Costs

     Have you ever wondered how the food and beverage manufacturing companies keep their facilities clean? After all, food is one of people’s basic needs and knowing where our food comes from makes us feel content with our choice.

     When it comes to cleaning and sanitizing their liquid tankers and process vessels, the food and beverage processors face many challenges on a daily basis. Thus, they use a variety of tools to make sure they produce quality products.

     One of the most useful tools in their arsenals is a process vessel camera designed to mount on a sight glass window. High-intensity discharge lamps are typically used to illuminate the interior of a process vessel such as a whirlpool or fermentation tank through separate sight windows. A vessel camera (see examples) can allow manufacturers to identify where sediments remain even after a rinse cycle with water from internal nozzles. Cameras can even help manufacturers save money by helping them to troubleshoot cleaning problems by spotting clogged or defective cleaning nozzles and identifying areas of the process vessel that required additional cleaning attention.

     One brewery was able to reduce their water usage significantly by identifying the sediment patterns that different beer recipes produced and adjusting their process vessel rinse cycles accordingly. By allowing them to monitor the entire process from beginning to end, the camera gave them the ability to determine which batches would produce the most sediment and where it would settle. A process vessel that was not thoroughly cleaned before the next batch was processed could have cost the manufacturer thousands of dollars in contaminated product that would have had to be discarded. To learn more about how a major U.S. brewer was able to pay for the cost of their lighting and camera system quickly by preventing product losses, we encourage you to take a few minutes to read our application note on this topic: 



6 Big Challenges in Sight Glass Construction

Is your sight glass tough enough to handle “The Big Six” challenges?

     Sight glass failures can be extremely dangerous. A sight glass that fails catastrophically has the potential for severe operator injury or death, as well as costly downtime and product losses. Even minor cracks, scratches or abrasions can create weakness within the sight glass, which will most likely lead to failure. In normal use, sight glasses are regularly subjected to forces involving extremes of pressure, temperature, thermal shock, caustics, abrasion, or impact.

      Our “6 Tips for Critical Sight Glass Applications” white paper provides expert advice on how to select a sight glass designed to withstand these challenges:

  • Temperature: Depending upon the temperature range, certain glass types will perform better than others. At less than 300°F, standard Soda Lime glass may be used. For temperatures up to 500°F, borosilicate glass may be used. At higher temperatures such as in high temperature steam applications, we recommend quartz or sapphire glass.
  • Thermal Shock: Some glass types are particularly vulnerable to cracking as a result of rapid temperature change, due to their low toughness, low thermal conductivity, and high thermal expansion coefficients.
  • Corrosion: Materials in process media like hydrofluoric acid, hot phosphoric acid and hot alkalis can etch the glass, producing a cloudy view with weakened integrity that requires the sight glass to be replaced.
  • Abrasion: Fluids that contain granular particles in suspension, or with particles carried in process gasses can abrade and erode a site glass, limiting visibility and affecting its strength.
  • Pressure: The glass materials selected, the unsupported diameter, and the glass thickness all play a role in determining the pressure capabilities of a sight glass assembly. Fused sight glass windows offer high pressure ratings and high safety margins. The strongest fused sight glasses are made from duplex stainless steel and borosilicate glass; this combination creates the highest compression.
  • Impact: Objects that strike the sight glass are seldom sufficient to cause immediate failure, but they can create scratches or gouges that provide a point for tensional force to concentrate. Scratched sight glasses should be replaced immediately.

     For details on how to take on these challenges, download our free copy of the “6 Tips for Critical Sight Glass Applications” white paper.

Compression Trumps Fusion in Sight Glass

“Fusion” is fine for fancy restaurants, but “compression” makes the real difference in sight glasses.

     Low-pressure bolt-on sight glass“Fusion” is sometimes used to describe cuisines that combine ingredients and cooking techniques from different cultures.  However, fusion is also sometimes used to promote some brands of sight glasses based on the belief that greater fusion of glass to metal during the manufacturing process will produce a stronger finished sight glass for use in chemical and pharmaceutical processes.

During manufacturing, the glass is melted within the metal ring as the ring expands. Then, temperature is raised to the point where the glass and the metal ring fuse together. When the unit cools, the glass hardens before the metal ring shrinks back to its original size. This places the metal ring in tension and the glass in uniform radial compression. The most compression is produced by using an alloy of metal that shrinks a lot as it cools in combination with a type of glass that shrinks little when it cools: the greater the difference, the greater the compression. Fusion – getting the glass to stick to the metal – is easy to achieve but not as critical to sight glass reliability as compression. Compression strengthens the glass because it is stronger than tensile forces that could create internal torque on the glass. Therefore, it is the level of compression, rather than fusion, that predicts the reliability of a sight glass.

A recent study shows that the combination of glass and metal that provides the most compression also provides the highest strength. The study compared a sight glass made of soda-lime glass and a Duplex stainless steel frame with a borosilicate sight glass (also with a Duplex stainless steel  frame) to analyze the amount of radial compression created by the difference between the glass and the metal in coefficient of thermal expansion as the sight glasses cool. The analysis showed the borosilicate glass produces significantly more compression than one made with soda lime glass. Also, there is a direct relationship between the amount of compression and the strength of the sight glass. The borosilicate sight glass has far greater pressure capability. Strength is also important for worker safety and because it reduces the need for sight glass maintenance and replacement.

The study also compared the compressive force of a sight glass made with proprietary soda-lime glass coupled with a Hastelloy C22 stainless steel ring (which is touted for its high glass-to-metal fusion) with that of a Duplex/borosilicate sight glass. The borosilicate glass/Duplex stainless steel construction provided four and a half times the pressure capability of the soda-lime/Hastelloy sight glass. The reliability of a sight glass has almost nothing to do with fusion; compression is what matters most because it secures the glass to the metal and creates a leak proof seal. Click here to see a full line of borosilicate sight glass products.

For all the details on this study, take a few minutes to read the white paper on compression vs. fusion.


Let There be (More) Light!

You may remember the old story about a man who is looking for his lost keys beneath a streetlamp. A passerby asks the man if he is sure about where he dropped them, and the man says, “Actually, I think I dropped them in the grass over there.” The passerby asks, “Then why aren’t you looking where you dropped them?” The first man answers, “Because the light is better here.”

On a street corner or in a processing facility, sufficient light makes all the difference in spotting what you need to find. The interiors of vessels and pipelines are typically far too dark to allow operators to observe important stages of their process readily through a sight glass. Flashlights usually don’t cast enough light and often produce glare, complicating the inspection process. Luminaires mounted onto sight glasses offer a more effective solution. Many processes take place in hazardous environments where explosive conditions may be present. For these applications, explosion proof lighting combines safe interior illumination and glare-free viewing.

There is a wide variety of explosion-proof sight glass lights to choose from. When choosing a light for a specific sight glass application, consider factors like type of technology, size, weight, voltage, wattage, materials of construction, mounting configuration, and light pattern. Energy consumption, location requirements, heat output, ambient conditions, and vibration must also be taken into account.

The “Understanding and Specifying Sight Glass Lighting” handbook addresses these considerations to help specifiers choose the most appropriate lighting solution for the application. Download your free copy today: http://www.sightglassblog.com/blog/03.html.