Internal Liquid Level Displacer Switch
Model FL

The Model FL is a top mounted displacer level switch. The "FL" can be used in a wide variety of applications. This level switch is available for models with up to 3 switches and field adjustable differential.


Mounting: The standard mounting connection is 4" 150# ANSI RF carbon steel flange. Flanges of other sizes (3" minimum) and material are available.
Displacers: Displacers are available in porcelain or stainless steel.
Trim: The rod and related hardware are standard in 300 series Stainless Steel. The spring is standard in inconel.
Immersion: Ten feet of cable is standard. Longer or shorter cables are available; from 2 feet to a maximum of 50 feet.
Differential: The differential can be either narrow or wide. This is not stage dependent. A wide differential is achieved by adding an additional stage or by using 2 displacers with a single stage. With the single stage switch control, the minimum differential is approximately 5/8". The location of the level points is adjustable.
Switch Housing: A water-tight/dust-tight or hazardous rated housing is available. Hazardous housing is rated to:

  • Class I, Groups B,C,D
  • Class II, Groups E,F,G
  • Class III
  • Class I, Zone 1, AEx d IIC
  • Ex d IIC
  • Type 4X
  • IP 66
  • 4X, 7BCD, 9EFG

and listed as:

  • FM Standard 3615
  • UL Standard 1203
  • CSA Standard C22.2 No. 30
  • NEMA Compliance
  • UL 60079-0/UL 60079-1
  • CSA 60079-0/CSA 60079-1
  • ATEX Directive 94/9/EC
  • UL 50
  • IEC 60529

Conduit Connection: 3/4" NPT is standard, 1/2" NPT or M20 are available.
Switches: See Model OF or Z.
Cable: 316 SS.


The operation of a displacer level switch differs from a float because the operation is based on weight displacement rather than buoyancy. In the low level position, the weight of the displacers will expand the displacer spring and keep the actuating piston out of the magnetic zone of the switch assembly. As the liquid rises the spring senses the weight change and will compress, lifting the actuating piston into the magnetic operating zone of the switch assembly. In doing so, a plunger is depressed, actuating a micro switch. As the level descends, the switch assembly will stay actuated until the weight of the displacers is sufficient enough to stretch the spring and pull the piston out of the operating zone. This will release the permanent magnet, re-setting the switch assembly to its unactuated position.