How a Pneumatic Liquid Level Switch Operates

What is a liquid level float switch? 

A liquid level float switch is a control device used as a High Level and/or Low Level switch in a pressurized production vessel. The switch sends a pneumatic signal, which can be used to actuate a control valve open or closed.

A liquid level switch is used to maintain desired level in separators, scrubbers, treaters, and other vessels. 


how does a liquid level float switch Work? 

Supply Pressure Coming Through Filter of Liquid Level Switch

There are two types of liquid level switch: electric and pneumatic.

In Kimray's pneumatic liquid level switch, supply pressure comes in through the filter, into the pilot body, creating a force on the stem, keeping it closed.

The float lever is magnetically opposed to the magnet in the shuttle which has a check ball on the top and bottom to seal off the flow in either direction. In the closed position it repels the shuttle downward, blocking the flow of supply gas to the diaphragm.

Diaphragm Creating Seal to Block Vent Path in Liquid Level Switch

  • As the liquid level rises and the float moves up, the float lever pivots down, repelling the shuttle up. This means the channel for the supply pressure to contact the diaphragm opens. This creates enough force to push the stem outward so that the supply pressure can flow to output. The diaphragm also creates a seal, which blocks the vent path.

    A pneumatic dump valve then receives an output signal telling it to open, which dumps liquid—typically either oil or water—from the vessel.
  • As the liquid level and float move down, the lever pivots upward, repelling the shuttle back down. This blocks the pressure to the diaphragm, which allows the stem to close with the O-ring sealing on the beveled surface.

    With pressure no longer on the supply side of the diaphragm, the pressure from the output port pushes the diaphragm to flow out to vent.
  • For manual actuation of the switch, after being installed in the vessel, there is a manual override button on the top.


different types of float switches

Kimray's Liquid Level Switch Extension Options

  • The Kimray pneumatic level switch comes direct-acting standard. However, you can easily switch it to indirect-acting by rotating the pilot body 180 degrees.If you need an extension to give the float more clearance, we offer a 3” extended version.
  • We also offer an electric version of the level switch.
  • If you need to control the level from outside of the vessel, we offer a compact, external float cage that works with both the pneumatic and electric level switch.

If you have questions about this or any other Kimray product, contact your local store or authorized distributor.