46-605 Flanged External Cage Float Actuated Liquid Level Switches
7
2.0
Reference Information
2.1
Description
Flanged External Cage liquid level switches are completely
self-contained units designed for side mounting to a vessel
or tank with threaded or flanged pipe connections.
2.2
Theory of Operation
The design of float-operated level switches is based upon
the principle that a magnetic field will not be affected
by non-magnetic materials such as 316 stainless steel
The float moves a magnetic attraction sleeve within a
non-magnetic enclosing tube and actuates a magnetic
switch mechanism. The enclosing tube provides a pressure
seal to the chamber and therefore to the process.
2.3
Operating Cycle
As the liquid level rises in the chamber, the float moves the
magnetic attraction sleeve up within the enclosing tube
and into the field of the switch mechanism magnet. As a
result, the magnet is drawn in tightly to the enclosing
tube, causing the switch to trip making or breaking an
electrical circuit. Refer to
Figure 4
.
As the liquid level falls, the float drops and moves the
attraction sleeve out of the magnetic field, releasing the
switch mechanism magnet. The tension spring ensures the
return of the switch in a snap action. Refer to
Figure 5
.
Tandem float units incorporate two floats which operate
independently. They are arranged so that the lower float
actuates the upper switch mechanism while the upper float
actuates the lower switch mechanism. The upper float is
attached to the lower attraction sleeve by means of a hol-
low stem. The lower float attaches to the upper attraction
sleeve with a solid stem which extends upward through the
upper float and stem assembly.
2.4
Switch Differential Adjustment
The standard differential of Flanged Cage float models
with one switch may be field adjusted. Adjustment may be
necessary if a wider differential needs to be set to overcome
switch chatter caused by the process.
NOTE: This procedure may be applied to single switch models only.
Enclosing tube
(non-magnetic)
Sleeve (magnetic)
Float
Normal
operating level
Magnet
Return
Spring
Pivot
Figure 4
Low level
Swing out
position
Figure 5
