The foundation of any level measuring system rests upon the level gauge itself, and for many fluidprocessing industries the new platform of choice is the magnetic level gauge. Almost half of all magnetic level gauges sold to engineers today are used to replace older sight glass units.
In the past, a sight glass was felt to be simpler because it does not have a float. Yet, close scrutiny reveals that a slight glass can possess as many as 50 separate parts. Additionally, the continuous maintenance required to remove and clean the glass is quickly forcing them out of favor. Some users have indicated a six to twelve month payback in maintenance savings alone by replacing their sight glasses with magnetic gauges. The fact that the cushions and gaskets used to seal the glass can be permanently deformed by compression —resulting in possible leaks, stress points, and even potential breakage—is likely the ultimate reason for the demise of sight glasses. This older technology clearly represents a substantial risk for environmental and personnel safety.
A quick review of how magnetic level gauges operate helps to further point out the reason for their increasing acceptance. Whereas a sight glass indicates level by visually displaying fluid level through direct contact against a measuring grid, magnetic level gauges display level through a separate tube that does not contain the process fluid, hence they are sometimes referred to as bypass level indicators. An magnetic level gauge is still a visual indicator of liquid level, but it utilizes magnetic transmission to couple the position of a float (housed within an external “float” chamber alongside the process fluid vessel) to a moving shuttle (indicator) housed in a closely approximated separate tube that is totally isolated from the fluid. As the fluid level is repeated in the float chamber, so is it represented in the indicator tube.
Since the visible shuttle/indicator avoids direct contact with process liquids, problems with coating, plating, fouling, fugitive emissions and hazardous material leaks are completely eliminated. This ensures safe leveling of liquids that are toxic, corrosive, or flammable. Magnetic coupling also makes it easier to determine the level of colorless fluids.