Level indicator in the steam boiler

Level indicator in the steam boiler: steam boiler with glass level gauge LGG

In steam boiler systems or hot water boiler systems, a continuous level indicator without auxiliary power is often required. Particularly when high temperatures and/or pressures prevail, special safety precautions must be taken. For steam boilers, the EN 12953-6 standard prescribes sight glass gauges, which must be a device with an indicator column made of transparent material. The medium must be visible.

This requirement applies to all industrial steam boiler systems and hot water boiler systems, e.g. in

  • car washes,
  • hospitals,
  • food industry,
  • automotive industry,
  • chemistry,
  • petrochemicals, oil and gas production,
  • shipbuilding,
  • mechanical engineering,
  • energy plants and power plants.

Functional principle of the sight glass level indicator LGG

Level indication in the steam boiler: glass level gauge LGG, installation at a steam boiler

This level indicator works on the principle of communicating tubes (bypass). The built-in sight glasses allow a direct view on the medium.






The display comes in three variants:

  1. Reflex glasses per DIN 7081
    In the viewing direction, incident light strikes the reflective grooves of the sight glass plate and is refracted into the liquid present. With gases, the light is reflected. Thus the level is visible as a dark column, the gaseous area as a silvery column over it. Reflex glasses are very well suited for the display of clear liquids.
  2. Transparent glasses per DIN 7081
    From the rear, incident light passes through both sight glass plates with the media between them. The level is visible as a line (meniscus) or directly due to the liquid itself.
  3. Refraction principle with mica shields
    From the rear, incident light from a lamp passes through both mica shields with the medium between them. The lamp and medium are arranged at an angle. In the gaseous phase, the light passes directly through, with liquid, the light is refracted sideways. Thus the level is visible as a black column, the gaseous area as a light column over it.


Type selection

These features characterize the LGG bypass sight glass gauges:

  • Continuous level indicator without auxiliary power
  • Process and procedure-specific manufacturing
  • Operating temperature: T = -196 ... +374 °C
  • Operating pressure: vacuum up to 250 bar
  • Meets the requirements of the EN 12953-6 standard
  • Large variety of different process connections and materials
  • Lighting optional
  • Heating and/or insulation optional

Füllstandanzeige im Dampfkessel: Schauglasanzeiger LGG-E

The standard version LGG-E is suitable for many applications up to 40 bar and +300 °C.

Special versions are available for higher pressures (up to 250 bar), very high temperatures (up to +374 °C) or for long glass tubes (up to 4.5 m).






Glass level gauges LGG - model overview

Glass level gauges LGG - model overview



  • All LGG devices meet the DIN EN 12953-1 standard for steam boilers. They are direct indicators, which make the medium directly visible through the sight glasses.
  • The LGG devices meet the requirements of the EU Directive 2014/68/EU (Pressure Equipment Directive, DGRL).


We would be happy to advise you on your special level measurement applications. Please contact us.

Attachment Size
Data sheet glass level gauge LGG 1.67 MB