Types of Sight Flow Indicators and Their Applications

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Sight flow indicators make monitoring fluids or gas inside a pipe easy and efficient. The device is installed into a pipe and offers a visual reference for liquid flow rate and direction. Operators can also see the clarity and color of fluids via a window. Used in a number of industrial applications, these tools are critical to measuring liquids accurately.

Types of Sight Flow Indicators

To monitor fluids in a process system, there are multiple different types of sight flow indicators available. Some applications require a full view indicator, while others need a more rugged option.

Sight flow indicators vary depending upon operational needs, but all quality sight flow indicators should adhere to industry standards including ANSI, ASME, ASTM, AWS, CSA, FDA and Mil-Spec. Different types include view-through, 360° view, flapper flow, drip, rotary flow, visual, and ball flow. Let’s dive a little deeper into each type:


With two opposing windows, operators can see a backlit fluid flow via ambient light or an attached light. These can be used with harsh fluids and high temperatures that some other indicators are not suited for and can be used for the widest range of applications overall.

360° View Flow

This cylindrical flow meter provides a full view while allowing liquid to pass through the tube. Enough ambient light passes through to offer good flow view, which is optimal for observing clarity and color. It is typically used for low-pressure systems with moderate flow rates.


Visible through the sight glass, this style features a hinged flapper deflected toward the flow direction, which gives an estimated gauge of the flow. It is usually seen installed on horizontal piping, but vertical pipes with an upward flow can also utilize this type of sight flow indicator.


To observe drip, this indicator allows for the view of low-volume intermittent flows and drips. With these, gravity is the key driver, and they are used most frequently with vertical pipes with a downward flow.

Rotary Flow

This flow meter is fitted with a rotor that is spun by a gas or fluid’s flow, it is a rotary flow style. It allows operators to view the direction, along with an approximate speed of the flow.


When an indicator is flapper-style and has a reset spring, it is considered a visual flow meter. The relative flow of the process fluid overcomes the force of the spring and a graduated scale on the glass visualizes the volume.

Ball Flow

A ball is pushed from the indicator’s bottom to the top of the window in this type of sight flow glass indicator. This movement indicates a flow is present in vertical pipes with slow upward flows.

Common Applications

Many industries have applications that require a tool to monitor the speed and quality of liquid or gaseous products or raw materials. Chemical or pharmaceutical companies, for example, might use sight flow indicators to monitor chemicals used in production.

Other manufacturers may use flow meters to monitor water or other chemicals within cooling or filtration systems. Additionally, sight flow indicators can be used internally inside of equipment or turbines to monitor fuel lines or hydraulic fluid flow and quality. Sight flow indicators may also be used in a number of municipal wastewater and environmental applications.

Each of the following industries is included among those that use sight flow indicators in some part of their operation:

●      Medical

●      HVAC

●      Marine

●      Pharmaceutical

●      Chemical

●      Industrial

●      Aerospace

●      Agricultural

●      Defense and military

●      Environmental

●      Food and beverage

Sight flow indicators play a critical role in measuring fluids in many applications across a wide variety of industries today. If a liquid or gas needs to be measured or monitored, chances are there is a sight flow indicator to function properly in the application for accurate results.




Image: U.S. Navy photo by Photographer's Mate Airman Apprentice Nathan Laird [Public domain], via Wikimedia Commons

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