Models T20 & T21 Single-Stage and Dual-Stage Float Switches

Single Stage Switch

T20 units are simple, reliable float switches, designed for top mounting into tanks or vessels. T20 units utilize a single switch mechanism and float. It can be used for virtually any type of open or closed process or storage vessel, with either threaded or flanged type mounting, and actuating depths of up to 48 inches (1219 mm).

Dual Stage Switch

T21 units combine the functions of two separate narrow differential level controls in a single, compact, easy-to-install instrument. Two independent switch mechanisms are employed to provide two actuating levels at least 8” apart, at actuating depths of up to 48 inches (1219 mm), for applications such as high and low level alarm operation. Model T21 tandem float switches are available with optional cages to help stabilize the floats under turbulent conditions.

Operating Principle

The buoyancy force of a process liquid on the float causes the float to move with the liquid surface. The movement of the float moves an attraction sleeve into the field of the switch magnet, pulling the magnet toward the sleeve and actuating the switch.


Day tanks
Fuel storage tanks
Flash tanks
Condensate Receivers
Cooling towers
High and high/high alarm from single tank entry


Float diameters of 3" × 5", 4" and 4 1⁄2" available
Tank connections available in 1" NPT, cast iron, forged, or stainless steel flanges
Maintenance free
Choice of switch mechanism:
Dry contact
Hermetically sealed
Choice of switch enclosure:
NEMA 1 carbon steel for pneumatics
TYPE 4X/7/9 Class I, Div. 1, Groups C & D, polymer coated aluminum
TYPE 4X/7/9 Class I, Div. 1, Group B, polymer coated aluminum


ATEX approved housing
Housing heater
Float guide cage
Tropicalized switch mechanism
Special flange face finishes
Submersible housing
Elevated temperature


XP=Explosion Proof (FM, CSA, ATEX)
ELV=EMC/Low Voltage (CE)
IS=Intrinsically Safe (ATEX)


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