Bi-colour Glass Liquid Level Gauge
BICOLOR GLASS LEVEL GAUGE
max. operating conditions:
pressure: 21,5 MPa (3000 psi) - temperature: 370 °C (700 °F)
Left drawing shows a typical Bicolor Glass Level Gauge, used for measurement of water level in high pressure boiler steam drums. This instrument consists of a stainless steel body having trapezoid cross section and machined to have a longitudinal chamber and front holes uniformly distributed on the two not parallel faces.
On each hole a special high temperature resistant aluminium silicate transparent cylindrical glass is tightly pressed between a metallic cover and the body by means of bolts and nuts. A mica shield protect the glass from the corrosive attack of the boiler basic water.
Belleville washers fitted between cover plates and glasses provide compensation of their different thermal expansion, giving guarantee of tightness at any operating condition.
The chamber is connected to vessel with cross fittings and flanged, threaded or welded ends.
For severe conditions (over 8MPa - 1116 psi water/steam pressure) water column and expansion joint are recommended.
Each Bicolor glass level gauge shall be fitted with top, bottom and drain shut-off valve. Automatic shut-off ball check can be supplied.
A special back illuminator (suitable also explosion proof) gives a sharp level reading by means of the contrast between bright color: green in lower part (liquid) and red in upper part (steam) of level gauge.
Bicolor level gauges can be equipped with long glasses instead of cylindrical glasses (as in Transparent Level Gauges).
Nevertheless we do not recommend bicolor long glass level gauges for steam drums over 10 MPa (1450 psi).
BONETTI Bicolor Glass Level Gauges are designed and manufactured in accordance with ASME BOILER AND PRESSURE VESSEL CODE - SEC. I.
WORKING PRINCIPLE:
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When in operation, bicolor level gauge shows to the observer port holes lighted green in the water zone and port holes lighted red in the steam zone. In case of long glass gauge, the window appears part green and part red.This result is obtained exploiting the following optical principle:
different colors (in this case: red and green) have a different index of refraction when passing obliquely through different media (in this case: glass, water and steam).
For the purpose, the gauge body has a trapezoid section with glasses placed on the non parallel faces.
An illuminator with special red and a green filters is fitted on the gauge at the opposite side with respect to the observer. This special illuminator conveys light through the filters obliquely to the back glasses of the level gauge.
Said filters allow crossing only to red and green rays.
Such colored rays reach, through the back glass, the media inside level body.
When the gauge contains steam, green rays are considerably deviated and prevented from emergingby the observer side; then only red light, whose rays are smoothly deviated by steam, passes through the whole internal hole, reaching the observer. Conversely when rays find water, red rays are considerably deviated and lost inside the internal part of level gauge, green rays can reach the front glass and seen by the observer.
Bicolor Level Gauges can be outfitted with Remote Transmission of Signal by means of: Fiber Optics System "Red Cherry"®, (image on the left) or Closed circuit TV, or through the use of special "periscope" mirrors