Data Sheet

Level Instruments
D103219X012
Product Bulletin
11.2:Level
February 2015
5
Figure 4. Fisher 2100E Electric Liquid Level Switch
APPROXIMATE
SWITCHING POINT
LOCATION OF
OPTIONAL
SIGHT WINDOW
X0682
Fisher 2100 Liquid Level
Switches
Typically, 2100E and 2100 switches electrically or
pneumatically operate safety shutdown systems for
field processing equipment in oil and gas industry
applications
Switch construction comes in a left‐hand as well as a
right‐hand mounting version. The explosion‐proof,
hermetically sealed 2100E switch is offered as both a
factory mounting and as an electric switch retrofit to
the proven 2100 switch.
With the 2100E switch rising liquid level exerts a
buoyant force on the torque tube that either activates
or deactivates an electrical SPDT or DPDT switch
Figure 5. Fisher 2100 Pneumatic Liquid Level Switch
W9954-1
depending on the switching action desired. Falling
liquid level deactivates or activates the same switch
depending on the action desired.
When the 2100 switch is in the normal position with
the flapper against the nozzle, output pressure cannot
bleed off and remains the same as full supply pressure.
Rising liquid level exerts a buoyant force on the
displacer, producing a torque on the torque tube.
When the torque transmitted by the torque tube
exceeds the torque exerted on the flapper by the
magnet, the flapper snaps away from the nozzle,
allowing output pressure to bleed through the nozzle
faster than supply pressure can enter through the
bleed orifice. The reduced pressure in the output
signal line activates the shutdown or alarm system.
When the liquid level lowers, the falling displacer
forces the flapper into the field of the magnet, letting
the magnet snap the flapper against the nozzle and
causing output pressure to build to full supply
pressure.