Types of Level Gauges

 Level gauge is a device which is used to show the level of fluids in fields. Depending on the type of application used, the type of level gauge should be selected. Level gauge is a direct method for measuring the level.

Types of Level Gauges

Level gauge consists of a metal body, machined to have an internal chamber and one or more front windows. On each window a special high resistance glass is used with sealing joint and metal cover plate hold by bolts and nuts.

Level devices operate under three main different principles:

The position (height) of the liquid surface

The pressure head

 The weight of the material

Types of Level Gauge:

There are commonly 3 types of level gauges used:

Reflex level gauge

Transparent level gauge

Magnetic type level gauge

Reflex level gauge:

Reflex glass level gauges working principle is based on the light refraction and reflection laws.

Reflex glass level gauges use glasses having the face fitted towards the chamber shaped to have prismatic grooves with section angle of 90°. When in operation, the chamber is filled with liquid in the lower part and gases or vapors in the upper part.

The liquid level is well-known by different brightness of the glass in the liquid and in the gas/vapor zone. The reflex level gauges do not need a specific illumination. The day light is enough for seeing the level.

LIQUID ZONE :

This zone appears dark when the gauge is in operation the light ray’s incident on the external face of the glass are quite perpendicular to said face and, therefore, not deviated by the glass. These rays reach the glass/liquid interface with an inclination of approx. 45°. The critical angle glass/liquid is always superior to 45°.

Therefore the rays incident within the critical angle are refracted within the liquid and, since the internal walls of the gauge chamber are not reflecting, the rays cannot be seen from the outside. In fact the zone will appear dark, nearly black, to the observer.

GAS/VAPOR ZONE :

This zone appears silver bright to the observer. As for the liquid zone, the light rays reach the glass/gas-vapor interface with an angle around 45°.

Since this angle is greater than glass/gas-vapor critical angle, the rays are not refracted, but totally reflected making 90° turn, thus reaching the nearest glass/gas-vapor interface again with angle of 45°. For same reason they will be reflected and turned by 90° towards the observer, to whom the zone will appear silver bright.

Applications :

Reflex glass level gauges can be used in most of the fluids and applications.

Reflex level gauges cannot be used in certain cases as for example:

when the separation level between two liquids has to be read (interface)

when the process fluid is high-pressure water steam, since in this case the glass must be protected from the solvent action of the boiler water by using mica shields

Transparent Level Gauge:

Transparent level gauges are always fitted with two plate transparent glasses between which the fluid is contained. The fluid level is indicated as the result of the different transparency of the two media.

To protect glass surfaces from corrosive action of the process fluid, Transparent Level Gauges can be fitted with Mica shields. The transparent level gauge is particularly recommended for applications where the glass needs to be protected from corrosive fluids and high temperatures.

Applications:

• In corrosive fluid.
• The observation of interface
• the observation of the liquid color
• for steam with an operating pressure > 20 bar
• If repeated thermal shocks comes
• Mica Sheet use in transparent level gauge: Mica sheet are widely used in visual liquid level to protect the glass surface from the corrosive effects of hot alkaline or acidic solutions. Mica shields are also commonly used in steam water applications to prevent etching and the weakening of the glass

Magnetic Level Gauge:

The Magnetic Level Gauge is used to preventive security against leakage, environmental safety, sure and trouble free application with chemically aggressive, pollutant, harmful or poisonous, inflammable or explosive, optically similar fluid interface.

The magnetic level gauge works based on some elementary physical principles:

The principle whereby the liquid in communicating vessels is always at the same level

Archimedes’s principle according to which a body immersed in a liquid receives a buoyancy equal to the weight of displaced liquid

The principle of attraction between North and South poles of two permanent magnets and that of repulsion between like poles.

There is a float in a pipe chamber which is movement with level and up and down accordingly. A flag flower is clamped with chamber. The individual flags or the follower contain an alignment magnet that couples with the float magnets as the float moves up or down within the piping column.

Float movement rotates the flags and changes their color, the position of the follower, or point at which the flags change color, represents the true level.

According to the orientation of each magnet each cylinder will show externally half of its surface of one colour or the other. The indicating scale will be of one colour over the chamber area taken up by gas, or steam phase contrasting with the other colour (e.g. red) over the chamber area taken up by liquid phase.