A simple, yet effective means of ensuring that liquid flow is proceeding both smoothly and unhampered is a little innovation called a sight flow indicator. Essentially a ‘window’ into a pipeline, it can allow you to view the fluid traveling through it as well as determine if gas or other matter is present. In today’s article we are going to discuss a little bit more about sight flow indicators in general, as far as how they work, indicators available for monitoring sight flow, as well as what to ask when you are looking to obtain one. Without further ado, let’s talk about sight flow indicators!
How do sight flow indicators work?
At it’s most basic level, a sight flow indicator functions like having a window into a pipeline. You can look through it to see how the flow is proceeding through the pipeline. Generally this is not going to include electronics but rather visual aids to help you to determine what is going on inside (although LED lights are often employed to illuminate the flow for better viewing). Alternately a lamp attachment may be used to illuminate the flow and a sight flow indicator of the most basic sort boils down to essentially two sides of glass or other material that allows viewing of the flow in progress. There are, however, a number of indicators which may be used that help to interpret what is being seen inside, be it water, gas, dirt or other contaminants… in fact, let’s discuss a few of those now!
What kinds of indicators are available?
There are a number of indicators that may be employed in order to maximize the identification that may be done through your new flow window. So, what kind of options do you have? Let’s discuss the most popular, we’ll identify them for you and tell you how they work. The indicators you should consider are as follows:
- Ball-style Flow indicator – This type of indicator is used for vertical pipes and typically comes in two forms. The first form is a ball that is suspended within a glass dome and when flow is interrupted or impaired the ball will drop out of view. The second and more common form is simply a ball which moves within the viewing window from the top to the bottom to indicate that the flow is constant and unimpaired.
- Drip-style indicator – These are used in vertical pipes with a downward flow, typically utilizing a drip tube for sight indicator purposes so that you may determine if a distillation flow is proceeding properly.
- Flapper-style flow indicator – This type of sight flow indicator is best for horizontal pipes but may also be used for vertical pipes as well. In this method, a hinged ‘flap’ is visible within the viewing area and the severity of its angle helps to determine the flow status and strength.
- Flutter-style indicator – Popular in Teflon-coated pipes, this method uses a thin strip of material which may be observed as flow proceeds. The strip will ‘wiggle’ either lightly to indicate a weak flow or more aggressively when displaying a strong flow travelling through the pipeline.
- Rotary-style flow indicator – One of the most common styles of sight flow indicators, the rotary-style flow indicator employs a rotor which will turn clockwise or counterclockwise depending on the direction of the flow. The speed of rotation is a visual indicator as to the strength of the flow and these may be employed in both vertical and horizontal pipes as needed.
“The viewing pane can be compared to the position of the flap”
- Visual-style flow meters – Similar to a flapper sight flow indicator, a visual style indicator employs a spring which means that as the ‘flap’ is moved by the flow through the pipeline that a scale marked on the viewing pane can be compared to the position of the flap, giving a good indication of flow measurement. This is a fairly inexpensive form of sight flow indicators that may be employed in a number of scenarios to ensure proper flow may be observed.
How do you select a sight flow indicator? 
So, how do you know which sight flow indicator to select? There are a few ground rules which you can follow that can help to make the decision much easier. When you are selecting a sight flow indicator, be sure to consider the following:
- What is going to be the function? – Is the pipe vertical or horizontal? Do you want to use a visual style with a gradient scale based on flapper angle or is a ball-style that easily indicates full-flow going to be adequate to your needs?
- What style of indicator do you need? – Some indicators are going to consist of two panes of glass with the indication medium suspended within. Another iteration that you might see consists of a glass cylinder illuminated by ambient light for reading from any angle. The latter is not so good for high-pressure scenarios but if you are not monitoring a high pressure flow pipeline then you might want to go the cylinder route.
- How will it be mounted? –Sight flow indicators can be obtained in a ‘clamped’ attachment type (which makes for easier cleaning) or alternately, bolted or threaded.
- Which materials are best suited for your purpose? – Stainless steel and carbon steel offer the best resistance and are most commonly used, although it is possible to obtain a Teflon coating in cases where a more aggressive flow is anticipated.
In Closing
In today’s article we have advised you in regards to the form, function, and selection of a sight flow indicator in order to monitor the flow of aggressive or standard pipes with greater ease. While it seems like a simple concept, simply being able to visually observe that everything is functioning properly within a pipeline is a huge advantage and should be considered. Tracing down losses in pressure and interruptions to flow can be greatly simplified so you should definitely take a look and see for yourself how this technology can help you. Examples of some excellent sight flow detectors may be found here:
Click here for examples of Dwyer sight flow indicators
