Use of a sight glass is probably the simplest method of measuring liquid level. The sight glass is attached to the outside of the tank so that the liquid level can be seen through the glass. The sight glass is marked with graduations to allow the level to be measured. The main disadvantage of this method is that it only gives level indication local to the vessel.
A visual indication of the level can be obtained when part of the vessel is constructed from transparent material or the liquid in a vessel is bypassed through a transparent tube. The advantage of using stop valves with the use of a bypass pipe, is the ease in removal for cleaning.
Types of Level Gauges:
Transparent Level Gauge
Transparent Level Gauges employ two transparent glasses fitted with a liquid chamber on either side. The liquid level is indicated as a result of difference in the transparent properties of the two media. For water / steam applications, an illuminator is mounted on the rear side of the gauge with its light rays deflected upward into the water column.
This enables the observer to see illuminated surface of the water as the light rays impinged on the surface of separation between water and steam are reflected back to the eye of the observer.
Magnetic Level Gauge
A float-containing magnet follows liquid level in the liquid chamber, which corresponds to the level in the tank. Position
of the float inside the chamber is indicated outside by bi-colored flapper embedded with magnet by 180 Deg rotation and setting into uniform color along the traverse of the float.
Reflex Level Gauge
The principle of Reflex Level Gauges is based on the difference in the refractive indices of liquid and vapor. The liquid column is contained within the recess of the liquid chamber behind the sight glass, which is clamped to the gauge body. The sight glass has prismatic right-angled grooves on the side facing the liquid and vapor space. Light rays entering from outside the gauge are either absorbed or reflected depending upon whether they enter the liquid or vapor space. When the ray of light encounters the surface of one of the grooves in the vapor space, it is reflected to the opposite surface of the grooves and from there, totally reflected back to the direction of observation.
Thus, vapor space appears as silvery white. When the light ray encounters the surface of the grooves in the liquid space, it is totally absorbed, thereby making the liquid behind the glass appear black. These gauges are used for measuring the level in a vessel.
Simple Sight glass level indicator
Advantages
Disadvantages
- Not suitable for automated control.
- Maintenance – requires cleaning
Applications/Limitations
These are not highly suited for industrial applications as manual viewing and transmission of information is required by the operator.
Applications of such level measuring devices can be seen in tanks for the storage of lubricating oils or water. They provide a very simple means of accessing level information and can simplify the task of physically viewing or dipping a tank. They are, however, generally limited to operator inspection.
Sight glasses are also not suitable for dark or dirty liquids. This type should not be used when measuring hazardous liquids as the glass-tube is easily damaged or broken. In installations where the gauge is at a lower temperature than the process condensation can occur outside the gauge, impairing the accuracy of the reading.
Summary
Simple sight glasses are an older technology and are very seldom used for automatic control applications.
FAQs
When the light ray encounters the surface of the grooves in the liquid space, it is totally absorbed, thereby making the liquid behind the glass appear black. These gauges are used for measuring the level in a vessel.
What is a sight glass used to measure? ›
Sight glasses are transparent industrial glass that are used for observing levels of liquids or gases inside of a pipe, tank, or boiler. This is critical as it allows plant managers or engineers to look inside their systems without disrupting the flow of operations.
What are the disadvantages of sight glass? ›
The glass in a sight glass can become quickly discolored, thus decreasing level visibility, or it can acquire microfractures, which can become a personnel safety issue if left undetected. Liquid/liquid interfaces can be very difficult to read in a sight glass particularly if the liquids are of similar color.
What is the range of sight glass? ›
Sizes range from 6 mm through to 600 mm. Materials available include aluminium, carbon steels, stainless steels, duplex stainless steels and hastelloy.
What is a sight glass level indicator for tanks? ›
Level Gauge Sight Glass is suitable for direct indication of the medium level in all kinds of towers, tanks, tanks, boxes and other containers. Safety steel ball is installed in the upper and lower valves of the instrument.
What are the components of a sight glass? ›
Sight glass windows are comprised of transparent glass materials fused to metal frames that function as single-piece components.
How is a sight glass installed? ›
The sight glass is normally installed in the liquid line directly after the filter drier in systems with an expansion valve. Theoretically, the sight glass can be installed anywhere along the pipe run in the liquid line. however, positioning close to the expansion valve is particularly advisable.
What is another name for a sight glass? ›
A sight glass, which can also be referred to as a sight port window or a sight window, is an observation window that allows you to look at fluid stored under high temperatures, extreme pressures, and other extreme environmental conditions.
What are the two functions of a sight glass? ›
Often referred to as viewing glasses, they offer you a way to see the levels of liquids or gases that are traveling through a critical point of your design, monitor pressure changes, and virtually anything else that sight glass windows could allow you to do.
What is the difference between a flow gauge and a sight glass? ›
Sight glasses are monitoring equipment without indicating mechanisms. Flow indicators have internal components that are set in motion by the flow. Flow meters are fitted with a calibrated measuring scale and indicating flag.
The capability of Glass to withstand significant strain is very poor, and it breaks easily. The application glass also increases the cost of security. It is poor in heat preservation, leading to higher operating costs. Glare is the major issue in the glass façade building.
What are the pros and cons of glass? ›
The pros and cons of glass design
- Natural light has positive impact on workers. ...
- Reduces heating costs. ...
- Aesthetically pleasing. ...
- Health and safety hazard. ...
- Costly to cool buildings down. ...
- Sun glare. ...
- Do you think the benefits of glass buildings outweigh the negatives?
Glass is generally a brittle type of material, but its strength can be improved by adding laminates and admixtures to the formula. A superior property of glass is its workability which allows it to be shaped and molded during the melting process.
What is the working principle of transparent flat glass level gauge? ›
According to the light refraction and reflection laws, the light enters directly from the smooth surface of the glass and refracts inside the liquid, making this area become dark. However, if the light hits the air part, it reflects, making this area become bright. In this way, the liquid level is observed.
How a level glass is used for interface indication? ›
The level is determined by a glass that has a smooth side and a wetted prismatic side. The level of the liquid inside the level indicator is shown using the optical principles of refraction: the wet part completely absorbs the light and that is why the liquid appears black.
How does oil sight glass work? ›
Oil sight glasses work by giving you a real-time snapshot of the oil inside your machinery without having to shut anything down. This live inside look plays a critical role in condition monitoring and early detection.
