Ametek Magnetrol B74 - Introduction; Principle of Operation; Operating Cycle; Installation

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46-635 External Cage Displacer Actuated Liquid Level Switches
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Figure 1
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Figure 2
1.0 Introduction
Displacer actuated external cage liquid level switches are
designed for service pressures up to 5000 psig (345 bar)
and liquids with specific gravities of 0.40 and above.
1.1 Principle of Operation
The design of displacer 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. In
this case, the displacer moves a magnetic attraction sleeve
within a non-magnetic enclosing tube and actuates a mag-
netic switch mechanism. The enclosing tube provides a
pressure seal to the chamber and therefore to the process.
1.2 Operating Cycle
The weight of the displacer ➀ is supported by the spring.
Rising liquid level imparts buoyancy forces on the displacer
allowing the spring to compress. The attraction sleeve ➁
attached to the spring, moves upward into the field of a
permanent magnet ➂. The movement of the magnet
toward the sleeve causes the switch ➃ to actuate. A non-
magnetic barrier tube ➄ provides a static pressure boundary
between the switch mechanism and the displacer assembly.
As the liquid level falls, the displacer lowers, moving the
attraction sleeve out of the magnetic field of the switch
mechanism. This allows the switch to again change position
and to break or make. See Figures 1 and 2.
2.0 Installation
Caution: If equipment is used in a manner not specified by manu-
facturer, protection provided by equipment may be
impaired
2.1 Unpacking
Unpack the instrument carefully. Inspect all units for
damage. Report any concealed damage to carrier within
24 hours. Check the contents of the packing slip and
purchase order. Check and record the serial number for
future reference when ordering parts.
On chambered units, remove the shipping strap and wire
assembly holding the displacer in place. This assembly
must be removed through the bottom chamber connection
before start-up.
Caution: If reshipping to another location, the displacer must again
be secured using the same strap and wire assembly.