It is also necessary to control the gas/liquid interface or the oil/water interface in process equipment. This is done with a level controller and liquid dump valve. The most common form of level controller is a float, although electronic sensing devices can also be used. If the level begins to rise, the controller signals the liquid dump valve to open and allow liquid to leave the vessel. If the level in the vessel begins to fall, the controller signals the liquid dump valve to close and decrease the flow of liquid from the vessel. In this manner the liquid dump valve is constantly adjusting its opening to assure that the rate of liquid flowing into the vessel is matched by the rate out of the vessel.
