The KING-GAGE® Rotameter Gauge has seen decades of service in all types of applications. This integrated bubbler system is not only remarkably accurate but also simple to use. Merely adjust the rotameter to an appropriate airflow for continuous tank liquid level indication. A custom calibrated scale permits direct reading in units of volume, weight, or depth.","5993 Bubbler Tank Gauge uses the proven technology in which a length of pipe extends downward into the tank liquid. When purged with compressed air, liquid within the downpipe is displaced by air pressure equal to the hydrostatic force of liquid in the tank. As the rotameter controls a low rate of flow, air pressure will constantly maintain equilibrium against the force of the liquid. Output is directly proportional to liquid depth. This device requires a source of compressed air (typically 55-60 psi \/ 3.9-4.1 bar) for operation.