Kerotest PE Valve
Liquid Level Gauges
Glass Level Gauges
Magnetic Level Gauges
Conductivity Electrode Level Gauge
Technical Notes - Level Gauges

Glass Level Gauges
Bonetti Liquid Level Gauges are available in various materials of construction, both transparent and reflex glass designs, as well as magnetic type for high pressures and temperatures up to 750F. We also supply Bi-color and Boiler Drum Level gauges.


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BONT  Reflex Level Gauges

The liquid level is distinguished by the different brightness's of the reflex glass in the water or in the steam space. Where there is liquid in contact with the glass, the incidental light is refracted to the inside of the gauge and absorbed; in the steam space, the incidental light is reflected against the glass grooves and the glass appears very bright.

Reflex level gauges can be used in most applications and offer great advantages in terms of low initial cost, low operating cost and easy level reading.

BONT Transparent Level Gauges

Apart from glass tube level gauges, 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 transparencies of the two medias and in some cases (for water steam), by conveying upwards onto the surface of light located at the back of the gauge. The rays are totally reflected down to the observer.

Transparent level gauges are suitable for almost all installations and permit:

  • the use of mica shields or Polytrifluorochloroethylene shields to protect the glass from the corrosive action of the process fluid
  • the observation of interface
  • the observation of the liquid color

BONT Bicolor Level Gauges

The two opposite glasses fitted into these bicolor level gauges are not parallel to each other. By means of a suitable illuminator into which red and green screens are fitted the portion of visible length occupied by steam appears red, whereas the portion of visible length occupied by water appears green. The level reading is very easy even at a considerable distance. The reading of the bicolor level gauges is not affected by the blind spaces between one port-hold and the successive one.

Bicolor Level Gauges main application is on high pressure steam boilers.

BONT Bicolor Level Gauges with Parallel Glasses

It is a variation of the Transparent Level Gauges, however equipped with two reflex glasses and a back illuminator, fitted with suitable colored filters. The sharp reading is given by the contrast between the bright color (usually red) of filters in the lower part containing liquid and the color of the upper part of visible window.

These level gauges are particularly suitable for liquids that are colorless, very fluid and non-corrosive for glasses (e.g. ammoniacal solutions, trichloroethylene, water steam up to 32 bar, etc.).

Magnetic Level Gauges

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Our magnetic level gauges are manufactured with the C to C and Visible Length requested by customers, up to approx. 6,500 mm for level gauges having a stainless steel vertical chamber and up to approx. 3,500 mm for level gauges having a vertical chamber in synthetic polymers. Longer C to C distances are manufactures with an intermediate flanged connection. Normally the visible length is equal to the Center to Center distance of the tank connections.

The BONT Magnetic Level Gauges are manufactured in different types and classes for various operating conditions. Plant operating and design conditions must be clearly indicated to choose a suitable level gauge. The selection of the level gauge depends  also on the specific gravity of the vessel liquid.


The BONT magnetic level gauge consists of:

  • a vertical chamber of a tube of suitable diameter and thickness containing a float wherein a permanent magnet is placed exactly on the liquid level line
  • two horizontal stub pipes for connection to the vessel containing the liquid of which we wish to know the level
  • two stop valves (recommended, but not mandatory) one on each stub pipe, to isolate the level gauge
  • an indicating scale, outside the vertical chamber, consisting of a case of non-magnetic material with transparent front face containing a set of small permanent magnets enclosed in small cylinders which can rotate on their horizontal axis. These cylinders show an external surface having two different colors.
Stainless Steel for PN 10/40 - 400 Synthetic Polymers Stainless Steel, PTFE Lined For Water/Steam
up to 210 bar pressure
Float Immersed in Vessel
If you want to use a level gauge for conditions different from those to which it was originally supplied, please contact our Engineering Department by phone at 919-806-3880 or via email at

Conductivity Electrode Level Gauge - Series RLG

Bonetti electrode type level indicators RLG series (Resistive Level Gauge) are made up of three main components:

  • RLG/C pressure water column
  • RLG/E electronic metering, monitoring and transmission unit
  • RLG/P conductivity electrode

The electronic unit (RLG/E) detects the presence of either water or steam around one or more electrodes (RLP/G) by measuring the conductivity between the electrode tips themselves and the water column metallic wall (RLG/C). A suitable number of electrodes are fitted to the column at different levels. The electronic unit (RLG/E) measures the water level within the column (RLG/C) detecting the number and position of the wet electrodes (RLG/P).

Bonetti electrode type level indicators RLG series are the ultimate solution to water level monitoring under high pressure and high temperature conditions. They provide high reliability while providing easy remote signal transmission. Their primary application is in steam boiler drum water level monitoring and signal transmission to the control room in thermoelectric power plants.

The conductivity sensor probe RLG/P is the heart of the RLG level indicator. It is made of stainless steel with a ceramic insulating element. The hydrostatic sealing consists of special graphite gaskets. Each probe is individually tested, both with helium and hydrostatically at 420 bar to verify sealing and function.

Click here to view the Catalog (pdf)  

View our Technical Notes on Level Gauges:     Level Gauges Technical Notes (pdf)

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