46-635 External Cage Displacer Actuated Liquid Level Switches
5
Conduit Outlet
Shut-Off
V
alve
Drain Valve
Max. 12"
P
ressure
V
essel
HL
L
L
Figure 3
Typical Piping Arrangement
2.2 Critical alarm function
It is recommended that for critical alarm functions, an
additional level switch be installed as a high–high or low–
low level alarm for maximum protection.
2.3 Piping
Figure 3 shows a typical piping installation of a displacer
control to a pressure vessel. An instruction tag secured to
the control gives dimensional data on switch actuating lev-
els referenced from center line of upper side tank connec-
tion. Position control so that actuating levels correspond
with the desired liquid level trip points in process vessel.
Use pipe of sufficient strength to support the control. If
necessary, provide a stand or hanger to help support its
weight. All piping should be straight and free of “low
spots” or “pockets” so that lower liquid line will drain
towards the vessel and upper vapor line will drain toward
the control. Shut-off valves are recommended for installa-
tion between the vessel and the control. If control is to be
used with a low temperature liquid (one which will “boil”
in the float chamber if outside heat is absorbed), the
chamber and piping should be insulated. Such boiling in
the chamber will cause false level indications.
DO NOT INSULATE SWITCH MECHANISM
HOUSING.
On controls equipped with pneumatic switch assemblies,
consult bulletin on mechanism furnished for air (or gas)
piping instructions.
Caution: Operation of all buoyancy type level devices should be
done in such a way as to minimize the action of dynamic
forces on the float or displacer sensing element. Good
practice for reducing the likelihood of damage to the con-
trol is to equalize pressure across the device slowly.
Switch Series
Letter
Description
Bulletin
No.
B, C, D Dry Contact Switch 42-683
F, 8 Hermetically Sealed Snap Switch 42-799
HS Hermetically Sealed Snap Switch 42-694
J Bleed Type Pneumatic Switch 42-685
K Non-Bleed Type Pneumatic Switch 42-686
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