Gauge body of this type is formed of a trapezoid in its cross sectional view so as to form a prism when a clear liquid comes in contact with opposing two glasses. With this devising and with the aid of an illuminator installed at the rear of the gauge to provide with red and green lights, level of the liquid can be clearly recognized by the boundary of the two colors, that comes up with the difference of refraction caused by existence or non-existence of the liquid. Since the gauge of this type is functional only with clear, transparent gas and liquid, it is mostly used for boiler applications which are worked with water and steam.

✔︎ SW4 series is used mainly for steam services under low to medium pressure. For mounting manner of the gauge on the drum, there are direct mount by use of a buffer pipe (called Expansion pipe) which is to absorb the thermal shock of the gauge under the high temperature operation. Remote level monitoring can be done clearly owing to brilliant two color level indication of the gauge. Mirror watching device consisting of reflection mirror and ducts, and ITV monitoring are also applicable.

✔︎ SW6 series is the standard two-color level gauge for medium and high pressure steam services. As SW6 series is used under higher pressure/temperature conditions than SW4 series, mounting manner of the gauge is generally an off-set type by means of buffer pipe (expansion).

✔︎ SW12 series was developed to follow up the tendency of thermal or nuclear power plant equipments toward higher pressure/temperature applications aiming at more highly efficient power generating system. The gauge glasses are being embedded in cover so as to receive no direct excessive load of tightening stress, enable to withstand the heavy tightened load in order to increase the sealing capacity. With the aid of two color illuminator, remote monitoring can be done by reflection mirror and ducts or ITV monitoring system. Great number of the model has been used for the high pressure steam drums and the incineration power plants in the world.