Bi-Colour Level Gauge

On a steam drum, the direct-reading water-level gauge is the reference every other level instrument is checked against, and in most jurisdictions it is required by the boiler code. The bi-colour gauge makes that reading unambiguous. Light passes through the gauge chamber at an angle; where there is water it refracts and appears green, where there is steam it appears red. There is no float and no signal to interpret, just two colours visible from across the boiler house.

Gauges are built for drum conditions to 210 bar and 450 °C in carbon steel or 316 stainless steel, with visible ranges from 95 to 2,480 mm in single or multiple sections. Mounting is side-side, side-bottom, top-side or top-bottom to suit the drum nozzles. A sunshade protects the illuminator outdoors, pointers and pushers mark normal and alarm levels, and drain and vent valves allow blowdown and isolation.

For remote reading the illuminated image can be transmitted to the control room by fibre optics or camera, and electronic versions provide a 4–20 mA HART signal or relay contacts, with an Ex-rated power supply for hazardous areas.

Bi-colour gauges are used on steam drums, boilers, heat-recovery steam generators and deaerators in power generation, oil and gas, petrochemical and refining.