Reflex Level Gauge-Purpose, Principle, Construction & Applications

This article describes Reflex Level Gauge-Purpose, Principle, Construction & Applications. The Reflex level gauge is also known as Reflex Liquid Level Gauge, Gauge Reflex, or Reflex Glass Level Gauge. Reflex glass generally reflects the light that comes from outside. We know that refractive indices of liquid and vapor are different, based on this phenomenon reflex glass level gauges are designed. It is designed for safe, clear, and positive visual indication of process liquid level in vessels.

A Gauge Reflex level gauge is highly recommended for colorless liquids. They are used in applications involving high temperatures, pressure conditions, and the corrosive nature of fluids.

reflex level gauge

Purpose of Reflex Level Gauge

Reflex level gauge design involves measuring liquid levels in tanks under high pressure and temperature conditions.

Operating principle of Reflex Level Gauge

The Gauge Reflex level gauge indicator measures the liquid level based on light refraction and reflection laws. The reflex gauge glass determines the liquid or gas content of a sample based on the reflection and refraction of light passing through it.

In the reflex gauge, the prism-shaped contact surfaces are formed between the sight glass and the liquid. This viewing surface however is smooth. Whenever light enters the smooth side of the sight glass surface vertically, it is refracted within the liquid. It is not reflected by the reflex level meter’s inner wall.

working of reflex level gauge

As shown in the above figure, the area of the glass covered by a liquid appears dark due to the refraction of the light, and the area covered by gas or air appears bright (silver-white). It is because of the complete reflection of the light.

The reflection level indicator can there be used to detect changes in liquid levels by distinguishing between bright and dark areas.

Construction of Reflex Level Gauge

To provide convenience for the end user, Reflex Level Gauges are designed to be connected sideways to tanks as bypass tubes. However, they are specially made depending on the client’s needs.   

Reflex glass gauge indicator comprises of double flat-glass mounted opposite each other on a chamber. Through cover plates, studs hold the glasses together. The tank connections are equipped with safety valves to prevent liquid flow in case of a glass break. For a safe shut-off, the needed pressure depends on the manufacturer; it is typically a 2-bar minimum.

There are three main components in the gauge body: the standpipe, which holds the fluid to be measured, the reflex glass segments (DIN glasses), and the cover, which holds the glass to the standpipe.

components of reflex level gauge

Used in applications under maximum pressure of 250 Bar, temperature up to 350 ° C.

Chamber materials are available in a variety of metallurgy types. Carbon Steel (CS), Mild Steel (MS), Stainless Steel SS304, SS316, 316L, etc. The glass material is borosilicate. The reflex gauges are equipped with heat protection for higher temperatures.

The Reflex Level gauge is a tightly shut sealed enclosure with reflex gauge glass inside. Reflex gauge glass consists of a smooth face outside towards the operator. Prismatic grooves with a tight 90 degrees section angle toward the inner side of the liquid chamber. With flanges, the instruments are then connected to the vessel to be observed.

It provides a clear picture of the liquid level, and it reduces the risk of distortion or inaccurate reading, giving a clear, visual representation of the liquid level. Meanwhile, it can be used in a variety of combinations to expand the observation range. Furthermore, it has an automatic shutdown function that prevents accidental losses and casualties.

Characteristics of Reflex Level Gauge

Following are the characteristics a reflex glass gauge comprises with

Level appearance is accurate and clear

the reflex glass installed in the reflex gauge comprises ‎prism-type grooves that help to provide sharp clear line marks of level indication.  ‎

Boiling liquid reading

by manually adjusting the isolation valve at the inlet of the chamber, the boiling liquid bubbles can be reduced and a clear liquid level can be observed.

Rigid structured body

The body is forged, which is advantageous when it comes to liquids with high density and viscosity.


Adaptable to different container sizes and can expand viewing areas as needed.

Feature of self-closing

A steel ball inside the needle valve at both ends of the gauge functions as a check valve. In case of glass breaks, the steel ball will automatically close the liquid channel under pressure to prevent the liquid from flowing out. This will reduce economic losses and avoid casualties.

Resistant to high temperature and high pressure

At high temperatures and high pressures, it can provide stable liquid level measurement for a long period.


  • The devices, however, cannot show the separation between different liquids or the actual colour of the fluid.
  • In addition to a grooved structure, reflex glass can be smooth and elongated or circular. Sometimes the properties of this type of reflex glass inhibit an application.

Safety concerns

  • Isolation valves are provided on both ends of the reflex glass gauge.
  • The precision design of these industrial gauges allows for safe operation and accurate reading standards of any liquid level.
  • Additionally, these reflex-level glass gauges are assembled with a pair of automatic shut-off ball arrangements, and a non-return valve, which ensures their maximum level of safety.

Applications of Reflex Level Gauge

Liquid level gauges, such as reflexes, are commonly used to measure the level of liquids in water heaters, boiler drums, deaerators, and other types of containers. These are in the fields of chemical, petroleum, metallurgy, oils, power, pharmaceuticals, etc.,

Reflex glass gauges are widely used in petroleum, chemical, power, metallurgy, pharmaceuticals, etc.

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