Bicolor Glass Level Gauges

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:

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