Float type level switches consists of a float displacer in a chamber. This chamber has two nozzle connections to the vessel. Liquid flows through the lower nozzle to the chamber. Changing level of float inside the chamber is sensed by a sensor inside the transmitter.
The size of nozzle connections range from 1″ to 2″. A block valve is installed between vessel and chamber so that this instrument can be maintained without disturbing the process.
Another type of level control instrument is based on an internal ball, which is generally used in vessels containing viscous liquids. Unlike the housed displacer, the ball or float is immersed directly inside the vessel through a flanged connection, which is large enough for the assembly to be withdrawn for maintenance. These instruments have no block valve and are installed on the side or on the top of the vessel.
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